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Biohybrid Solar Cells: Fundamentals, Progress, and Challenges
Abstract
Over the last two decades many reports have been published on diverse types of biohybrid electrodes utilizing components of the photosynthetic apparatus. Currently, the development of such devices does not extend beyond laboratory research. In the future, these electrodes could be used in biosensors, solar cells, and as a new technique to investigate photosynthetic pigment-protein complexes. Efficiency of light-to-current conversion is particularly important for solar cell applications. Selection of a suitable substrate for special pigment-protein complexes is a significant challenge for building an inexpensive and efficient device. Various combinations of pigment-protein complexes and substrates, as well as different measurement conditions make it difficult to directly compare performance of various solar cells. However, it has been shown, that one of the possible substrate materials, namely nanostructured TiO2, is the most preferred material for the immobilization of pigment-protein complexes in terms of
both cost and efficiency. The photocurrent values reaching several mA, were reported for TiO2-based biohybrid electrodes. However, the efficiency of TiO2-based biohybrid is still far from its potential maximum value due to fundamental challenges related to designing an optimum interface between TiO2 nanostructure and pigment-protein complexes containing electron transferring cofactors. To date, counterproductive back reactions, also referred to as charge recombination, still dominate and lower internal quantum efficiency of these systems.
... They are tetra-pyrrolic macrocycles that are metalized by a complexed magnesium atom in their core and replaced by a phytyl chain. They may be found in algae, higher plants, and cyanobacteria [22]. In addition to presence P and Ca elements in all samples which was attributed to presence of wuxal medium [23]. ...
... The absorption peak at 485 nm was also indicated for carotenoid pigments in all selected microalgae [30]. However, in Ba9, The Phycobiliproteins absorb light in the visible region of 450-650 nm [22]. Furthermore, the peak intensity varied depending on microalgae strains, with Ba9 ...
... 1,2 Exploiting these sophisticated biological complexes in biohybrid devices has been a long-sought-after goal in bioengineering. 3 However, using natural photosystems in photovoltaic applications has proven difficult, partly because of poor protein stability and lack of control over the electron flow. Biohybrid solar cell efficiencies have thus fallen short of expectation, 3 trailing well behind established silicon (26%), 4,5 perovskite (24%) 6 , and dye-sensitized (13%) 7 solar cells. ...
... 3 However, using natural photosystems in photovoltaic applications has proven difficult, partly because of poor protein stability and lack of control over the electron flow. Biohybrid solar cell efficiencies have thus fallen short of expectation, 3 trailing well behind established silicon (26%), 4,5 perovskite (24%) 6 , and dye-sensitized (13%) 7 solar cells. ...
The global energy crisis challenges us to develop more efficient strategies for the sustainable production of energy. Given the excellent efficiency of the natural photosynthetic apparatus, biohybrid photovoltaic devices present an attractive solution for solar energy conversion. However, their composition, stability, and complexity can limit their inclusion into photovoltaic devices. Here, we combined computational design and directed evolution to overcome these limitations and create tailor-made photoenzymes. Photo-biocatalysts were designed by introducing photosensitizer binding sites into heme-containing helical bundle proteins. The designed binding sites were specific for the target photosensitizer and readily transplanted into other helical bundles. The best design was highly evolvable and reached nanomolar ligand affinity after mutagenesis and screening. The evolved enzyme generated 2.6 times higher photocurrents than the photosensitizer alone, primarily driven by increased photostability. Evolvability is a unique advantage of our protein-based approach over abiological photovoltaic and will be critical to developing efficient biohybrid systems.
Abstract Figure
... The cell efficiency improved from 10.4% to 13.5% by the energy transfer. [112] There are ongoing research investigations on nanostructures and natural dyes such as nanotubes, thin films, quantum dots, and NPs for PV cell applications [114]. This trend of PV cell research including exploiting nanomaterials in developing devices for collecting and converting solar and wind energies, harvesting fuel cells, and storage of energy will continue. ...
This research work provides concise insights into fossil fuel consumption challenges, and the factors contributing to global warming, and evaluates the significance of photovoltaic (PV) materials in achieving net-zero-CO 2 emissions. The article categorizes constraints in the development of PV cells into four main areas: technical factors, leadership impact, political instability, and financial aspects. Primarily, the study delves into technical factors, focusing on the power conversion efficiency (PCE) and power density of PV cells. Theoretically, approximately 67% of solar energy is dissipated in various forms:-47% as heat, 18% as photons, and 2% in local combination loss. Commercially available mono-crystalline silicon (c-Si) and poly-crystalline silicon (poly-c-Si) PV cells typically demonstrate a range of PCEs between 15%-22% and 13%-18%, respectively, presenting an efficiency considerably lower than the potential maximum of 100%. The study highlights organic photovoltaic cells (OPVs) as promising third-generation PV modules due to their relatively high power conversion efficiency (HPCE) and eco-friendly attributes. However, their commercial feasibility is under scrutiny owing to constraints such as a limited lifespan, high production costs, and challenges in mass production. Ongoing research and development (R&D) in PV cell technologies aim to enhance PCE and power density, establish cost-effective production methods, and create more reliable and sustainable supply chains. Additionally, the study explores the role of nanotechnology in developing high-power conversion efficiency cells, identifies research gaps and priorities in engineered organic material PV cells, and discusses the potential of OPVs in the R&D of high-efficiency, cost-effective, and environmentally friendly PV cells.
... Hydrogen-based energy includes production, storage, safety, and utilization steps (45). Light sources are crucial for bioH 2 production to control biological and physiological processes (46). Notably, two major drawbacks that bioH 2 production are currently facing are poor yield of hydrogen and a high manufacturing cost (47). ...
Managing waste and producing clean energy has been of interest to researchers during this century. Several methods to produce hydrogen (H2) gas were discussed in this study, with the findings revealing that electrolysis, photosynthesis in plants and algae, steam methane (CH4) reforming, and anaerobic digestion (AD) are possible H2 production methods. The pH and hydraulic retention time (HRT) are factors affecting H2 production and should range from 5.0-6.0 and 6-8 h, respectively. Cryogenic separation, adsorption, and absorption membrane separation can be used for H2 purification depending on the specifications and product gases. However, these techniques are expensive, affecting the affordability of H2 in the market. To address these challenges, alternative methods, such as the use of nanomaterials and photocatalytic water splitting, should be considered. In addition, this study demonstrated that biochar as a catalyst can significantly enhance H2 production. Therefore, further research is required to provide a comprehensive overview of the state-of-the-art raw materials used for H2
production.
... Photosystem I (PSI) is a photosynthetic pigment-protein complex which absorbs light and converts its energy into electric energy of charge-separated states where electrons reach a distance of up to~6 nm from the positive charge [1,2]. Therefore, it is often tested in different biophotovoltaic systems where it serves as an essential part in generating photocurrent [3][4][5][6][7][8][9]. In intact biological systems, PSI shows exceptionally high efficiency of absorbed photon-to-photoelectron conversion of~99%, and a significant voltage of~1 V in its fully charge-separated state [1,2]. ...
This study investigates the immobilization of cyanobacterial photosystem I (PSI) from Synechocystis sp. PCC 6803 onto fluorine-doped tin oxide (FTO) conducting glass plates to create photoelectrodes for biohybrid solar cells. The fabrication of these PSI–FTO photoelectrodes is based on two immobilization processes: rapid electrodeposition driven by an external electric field and slower adsorption during solvent evaporation, both influenced by gravitational sedimentation. Deposition and performance of photoelectrodes was investigated by UV–Vis absorption spectroscopy and photocurrent measurements. We investigated the efficiency of PSI immobilization under varying conditions, including solution pH, applied electric field intensity and duration, and electrode polarization, with the goals to control (1) the direction of migration and (2) the orientation of the PSI particles on the substrate surface. Variation in the pH value of the PSI solution alters the surface charge distribution, affecting the net charge and the electric dipole moment of these proteins. Results showed PSI migration to the positively charged electrode at pH 6, 7, and 8, and to the negatively charged electrode at pH 4.4 and 5, suggesting an isoelectric point of PSI between 5 and 6. At acidic pH, the electrophoretic migration was largely hindered by protein aggregation. Notably, photocurrent generation was consistently cathodic and correlated with PSI layer thickness, and no conclusions can be drawn on the orientation of the immobilized proteins. Overall, these findings suggest mediated electron transfer from FTO to PSI by the used electrolyte containing 10 mM sodium ascorbate and 200 μM dichlorophenolindophenol.
... The superior stability of those two complexes compared with their mesophilic counterparts and plants has later been adopted for biotechnological solutions like the construction of biohybrid devices such as biophotoelectrodes and biophotovoltaics (Kargul et al. 2012;Musazade et al. 2018) and remains along with the photosystems of extremophilic red algae of the order Cyanidiales (e.g. Cyanidioschyzon sp., Galdieria sp.) as the most promising solutions for light harvesting needed by biohybrid devices. ...
Thermophilic cyanobacteria are prokaryotic photoautotrophic microorganisms capable of growth between 45 and 73 °C. They are typically found in hot springs where they serve as essential primary producers. Several key features make these robust photosynthetic microbes biotechnologically relevant. These are highly stable proteins and their complexes, the ability to actively transport and concentrate inorganic carbon and other nutrients, to serve as gene donors, microbial cell factories, and sources of bioactive metabolites. A thorough investigation of the recent progress in thermophilic cyanobacteria reveals a significant increase in the number of newly isolated and delineated organisms and wide application of thermophilic light-harvesting components in biohybrid devices. Yet despite these achievements, there are still deficiencies at the high-end of the biotechnological learning curve, notably in genetic engineering and gene editing. Thermostable proteins could be more widely employed, and an extensive pool of newly available genetic data could be better utilised. In this manuscript, we attempt to showcase the most important recent advances in thermophilic cyanobacterial biotechnology and provide an overview of the future direction of the field and challenges that need to be overcome before thermophilic cyanobacterial biotechnology can bridge the gap with highly advanced biotechnology of their mesophilic counterparts.
Key points
• Increased interest in all aspects of thermophilic cyanobacteria in recent years
• Light harvesting components remain the most biotechnologically relevant
• Lack of reliable molecular biology tools hinders further development of the chassis
Graphical Abstract
... Significant research efforts have been made to build semiconductor/photoelectrode hybrids for high-efficiency PBECs, which will help to bring sustainable solar energy to a commercially ready state [3,4]. For this reason, several natural pigments have been investigated as biocatalysts in PBECs systems [5]. Plant or microalgae pigments are able to do this because their electrical structure may alter the wavelength of incoming sunlight, creating an electric current [6,7]. ...
An important part of a photo-bioelectrochemical cell (PBEC) is the photo-biocatalyst substrate taken as anode. This study aims to explain the effect of CNT/TiO2/chlorophyll photocatalyst coated on the cellulose nanopaper (CNP) substrate on the PBEC performance and to compare the results with those obtained for the commercial indium tin oxide (ITO) glass and flexible ITO as substrates. The results showed high sheet resistance of CNP, which is 61182 Ω sq-1, which is reduced by 80 % in the presence of CNT/TiO2/Chl biocatalyst. The highest output voltage of 0.95 to 1 V was produced by coating CNT/TiO2/Chl on the flexible ITO. The maximum current density (Jmax) of 3726 mA m-2 and the highest maximum power density value of around 574 mW m-2 were obtained for illuminated CNT/TiO2/Chl on the rigid ITO anode. In dark conditions, the highest power density was observed for CNP as the supporting substrate. The photo-bioelectrochemical cell adopting CNT/TiO2/Chl and CNP as the supporting substrate material has great potential for a variety of applications, such as wearable electronics, environmental monitoring, remote or off-grid energy supply, and renewable energy systems, thereby contributing to the advancement of sustainable energy technologies.
... The extensive consumption of traditional energy resources and their environmental impact have propelled the significant exploration of renewable energy technologies in recent years [1][2][3][4]. One particular area of interest is electrochemical water splitting, emerging as a leading approach for acquiring clean hydrogen energy [5]. ...
The oxygen evolution reaction (OER) is a key half-reaction in electrocatalytic water splitting. Large-scale water electrolysis is hampered by commercial noble-metal-based OER electrocatalysts owing to their high cost. To address these issues, we present a facile, one-pot, room-temperature co-precipitation approach to quickly synthesize carbon-nanotube-interconnected amorphous NiFe-layered double hydroxides (NiFe-LDH@CNT) as cost-effective, efficient, and stable OER electrocatalysts. The hybrid catalyst NiFe-LDH@CNT delivered outstanding OER activity with a low onset overpotential of 255 mV and a small Tafel slope of 51.36 mV dec⁻¹, as well as outstanding long-term stability. The high catalytic capability of NiFe-LDH@CNT is associated with the synergistic effects of its room-temperature synthesized amorphous structure, bi-metallic modulation, and conductive CNT skeleton. The room-temperature synthesis can not only offer economic feasibility, but can also allow amorphous NiFe-LDH to be obtained without crystalline boundaries, facilitating long-term stability during the OER process. The bi-metallic nature of NiFe-LDH guarantees a modified electronic structure, providing additional catalytic sites. Simultaneously, the highly conductive CNT network fosters a nanoporous structure, facilitating electron transfer and O2 release and enriching catalytic sites. This study introduces an innovative approach to purposefully design nanoarchitecture and easily synthesize amorphous transition-metal-based OER catalysts, ensuring their cost effectiveness, production efficiency, and long-term stability.
... In the same way, that evolution has introduced robust light-capturing antennae designs to photosynthesis, the efficiency of low bandgap semiconductors can improve solar panels by adding a material with a broad absorption spectrum. The most spectacular achievements in the area of bio-based solar panels too far have been obtained utilizing titanium dioxide (TiO 2 ) based bio-hybrid electrodes, such as those employed in the DSSCs [51]. ...
... The design of electrodes continues to play an important role as it is often the rate-limiting step. Furthermore, large absorption cross-section, anchoring of biomolecules onto substrates and stabilization of biomolecules onto electrodes are some of the design limitations that should be considered (Musazade et al., 2018). The evaluation of microorganisms in terms of stability and CO 2 reduction capacity should also be considered in any biohybrid system design. ...
... Among the commonly used matrices for immobilization of PS II protein-pigment complex are gold, TiO 2 , graphite, fluorine-doped tin oxide, or electrode based on indium tin oxide (ITO). Gold, TiO 2 , silicon, graphene, gallium arsenide(III), carbon nanotubes, and other nanoparticles or redox polymers are used in the case of PS I protein complexes (Musazade et al. 2018;Teodor & Bruce 2020). These immobilization techniques were mainly used to study the generation of current induced by continuous illumination. ...
In this minireview, we consider the methods of measurements of the light-induced steady state transmembrane electric potential (Δψ) generation by photosynthetic systems, e.g. photosystem I (PS I). The microelectrode technique and the detection of electrochromic bandshifts of carotenoid pigments are most appropriate for Δψ measurements in situ and in vivo. Direct electrometrical method and Δψ measurements in the photovoltaic system based on membrane filter (MF) sandwiched between semiconductor indium tin oxide electrodes (ITO) are suitable for studies of isolated pigment-protein complexes and small natural vesicles—chromatophores. In the presence of trehalose, ITO|PS I-MF|ITO system allows to keep a steady state level of ∆ψ after 1 h of illumination. According to preliminary experiments, this system is capable of providing steady state light-induced ∆ψ after several months of storage in the dark at room temperature under controlled humidity in the presence of trehalose. The long-term generation of light-induced ∆ψ in relatively simple system may serve as a source of the solar-to-electric energy conversion.
... Cyanobacterial hydrogen production and reducing CO 2 emissions (Schipper et al., 2019;Zebda et al., 2018). Biohydrogen synthesis requires a light source to manage biological and physiological processes (Musazade et al., 2018). ...
The taxonomic identification of cyanobacteria is essential for researchers or/and competent authorities to know their diversity and detect, manage, and control potentially toxic cyanobacteria. Microbiologists and botanists agree that polyphasic approaches are a powerful tool to identify cyanobacteria. This chapter describes the polyphasic approach, the steps to follow, and some recommendations for its correct application. The changes in taxonomy using this methodology are also explained. Finally, the applications of a polyphasic approach on genomic and metabarcoding biodiversity studies are described. The polyphasic approach is a well defined and standard tool for classifying cyanobacteria, which researchers accept, but it is continuously being revised.
... Cyanobacterial hydrogen production and reducing CO 2 emissions (Schipper et al., 2019;Zebda et al., 2018). Biohydrogen synthesis requires a light source to manage biological and physiological processes (Musazade et al., 2018). ...
Metals are essential elements for life, but they are particularly necessary for photosynthetic organisms. Here, we focus on how cyanobacterial photosynthesis responds to metal constrains, with especial emphasis on copper and iron. In particular, the photosynthetic machinery requires large amounts of iron, either as free ions or in heme and iron-sulfur cofactors. In response to the limitations and bioavailability of iron, photosynthetic organisms have developed alternatives to replace iron-containing proteins. Thus, in the photosynthetic chain of most cyanobacteria, flavodoxin (a flavoprotein) replaces ferredoxin (an iron-sulfur protein) on the donor side of photosystem I under iron-limiting conditions. In addition, when copper is available, plastocyanin (a copper protein) substitutes the heme-protein cytochrome c6 in the lumen of the thylakoid as the electron carrier from cytochrome b6f to photosystem I, and in connecting the photosynthetic and respiratory chains. In each of these pairs, both proteins have developed equivalent functional areas, resulting in a functional equivalence. However, the plastocyanin/cytochrome c6 couple exhibits intriguing parallel differences in different cyanobacteria.
The ferredoxin/flavodoxin and plastocyanin/cytochrome c6 expression is precisely regulated as a function of variations in iron or copper concentrations. Recently, the system regulating the copper-dependent cytochrome c6/plastocyanin switch has been described as composed by a transcriptional factor and a protease, the latter regulating the levels of the expression factor in response to the presence of copper.
... Thus, using algal biomass to produce hydrogen has various advantages, including waste management, substituting fossil fuels with long-term biofuels, and reducing CO 2 emissions (Schipper et al., 2019;Zebda et al., 2018). Biohydrogen synthesis requires a light source to manage biological and physiological processes (Musazade et al., 2018). ...
The production of cyanobacterial based hydrogen is an environmentally sustainable and economically feasible energy source, appears to be a viable alternative for the future. The current condition of the research in the area of cyanobacterial hydrogen production is described in the present study. Cyanobacteria are highly relevant and valuable as prospective hydrogen producers since as a result of the conversion of solar energy, they produce hydrogen from water. However, hydrogen production is a complicated biotechnological process with the primary stumbling block, cyanobacteria has limited ability to generate hydrogen at present, a complicated strategy for enhancing hydrogen production can improve the chances for the generation of hydrogen energy from cyanobacterial cells. This chapter summarizes current thoughts on cyanobacterial role in bio-hydrogen generation, and it explains every step involved in the process, scientific achievements, existing problems, suggests future research goals and objectives.
... The membrane-bound protein-pigment complexes in these systems are capable of catalyzing the photochemical charge separation with a quantum efficiency of close to 100% (Blankenship et al., 2011;Singh et al., 2018), which has inspired the exploration and development of the third-generation solar cells (O'Regan and Grätzel, 1991;Wang et al., 2020Wang et al., , 2021. The third-generation solar cells prepared by plant and bacterial photosynthetic complexes are collectively known as photobioelectrochemical cells (PBECs) (Feng et al., 2016;Sekar et al., 2016;Musazade et al., 2018;Zhou et al., 2019;Lee et al., 2020). ...
Roseiflexus castenholzii is an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, R. castenholzii RC-LH (rcRC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome c subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer. These novel structural features of the rcRC-LH are advantageous for enhancing the electron transfer efficiency and subsequent photo-oxidation of the c-type hemes. However, the photochemical properties of rcRC-LH and its applications in developing the photo-bioelectrochemical cells (PBECs) have not been characterized. Here, we prepared a PBEC using overlapped fluorine-doped tin oxide (FTO) glass and Pt-coated glass as electrodes, and rcRC-LH mixed with varying mediators as the electrolyte. Absence of the H subunit allows rcRC-LH to be selectively adhered onto the hydrophilic surface of the front electrode with its Q-side. Upon illumination, the photogenerated electrons directly enter the front electrode and transfer to the counter electrode, wherein the accepted electrons pass through the exposed c-type hemes to reduce the excited P+, generating a steady-state current of up to 320 nA/cm2 when using 1-Methoxy-5-methylphenazinium methyl sulfate (PMS) as mediator. This study demonstrated the novel photoelectric properties of rcRC-LH and its advantages in preparing effective PBECs, showcasing a potential of this complex in developing new type PBECs.
Self-organizing tissues, such as organoids, offer transformative potential beyond healthcare by enabling the sustainable production of advanced materials. Resource scarcity and global warming drive the need for innovative fabrication solutions. This prospective review explores developmental biology as a manufacturing process, where the material (e.g. spider silk) and its production unit are self-organized (e.g. silk glands). Biological systems orchestrate the emergence of hierarchical materials with superior mechanical properties and biodegradability, using abundant and renewable resources. Tissue engineering enables the creation of biological systems that surpass current synthetic designs in complexity. We highlight application opportunities, focusing on spider silk as a model to demonstrate how organs synthesize and assemble next-generation materials. The concept of growing both a material and its organ production units is exemplified by hair-bearing organoids, self-organized from induced pluripotent stem cells (iPSCs). Key challenges in expanding organoid research to new model species and scaling-up production are discussed alongside potential solutions. We propose a simplified description of these complex systems to help address key challenges. Furthermore, synthetic and hybrid approaches are explored, considering the ethical, societal, and technological impacts. Though still in their infancy, material-producing organoids present a promising avenue for sustainable, high-value products, fostering new interdisciplinary collaborations among bioengineers, developmental biologists, and material scientists. This work aims to inspire further exploration into the applications of self-organized biological systems in addressing global challenges.
Photosynthesis has garnered significant interest due to its potential for retrofitting and its intrinsic enzyme‐mediated metabolic processes, which can convert carbon dioxide (CO2) into biomass powered by solar energy. However, natural photosynthesis is limited by factors such as low photosynthetic efficiency and constraints on the range of output products. To address these issues, researchers have developed various strategies for designing and engineering photosynthetic systems. These strategies include nanomaterial‐assisted approaches to enhance light absorption and accelerate electron transfer, microfluidic technologies for precise manipulation of enzyme modules, synthetic biology techniques to optimize metabolic pathways, and photo‐bioelectrochemical systems (PBESs) for efficient utilization of photosynthetic electrons. Inspired by these, numerous applications have emerged in the fields of artificial organelles, promotion of hypoxic tissue healing, bioproduction, and environmental production and sustainability. This review provides a comprehensive introduction to the principles of photosynthesis, encompassing light and carbon reactions. Additionally, it offers an overview of recent strategies for the design, structuring, and engineering of photosynthetic systems, while discussing several applications of photosynthesis. Finally, this review highlights the potential of engineered photosynthetic systems to address challenges in energy and matter conversion across various fields, offering insights into the future of sustainable, photosynthesis‐based technologies.
Limited reserves of fossil fuels and the negative impact of their combustion products on the environment are two pressing problems of our time. The development of alternative energy sources, among which solar energy is the most accessible, is considered as a possible solution. Acquisition of skills of its effective and environmentally friendly use by creating artificial photosynthetic systems imitating the processes of natural photosynthesis, as well as the use of artificial photosynthesis for the production of biofuels can contribute to a way out of the current situation.
В основе центральных метаболических путей преобразования энергии лежит мембранный перенос электронов. Фотосинтетическая и дыхательная электрон-транспортные цепи представляют собой сложные аппараты, способные создавать трансмембранный протонный градиент, преобразуя солнечный свет или химическую энергию. Новаторское использование этих аппаратов в качестве преобразователей энергии представляет интерес ввиду доступности и экологичности биоматериала. Устройства, в которых для выработки электроэнергии используются хемотрофные микроорганизмы, известны уже более ста лет. В этих системах, именуемых микробными топливными элементами (MFC), один или несколько типов микроорганизмов катализируют перенос электронов от расходуемого субстрата (ацетата, глюкозы и т.д.) к электроду. В последне время активно разрабатываются MFC на основе фототрофных организмов. Эти устройства, именуемые фотосинтетическими микробными топливными элементами (РMFC), подобны обычным MFC в том, что в них для преобразования химической энергии в электрическую используются живые клетки микроорганизмов. Однако различие между этими двумя классами топливных элементов состоит в том, что в MFC используется только химическая энергия органического субстрата, тогда как РMFC способны также использовать солнечную энергию. Общим для них является способность использовать естественные электрон-транспортные цепи метаболизма бактерий в качестве основного механизма преобразования энергии. Благодаря общедоступности солнечной энергии, РMFC на основе фотосинтеза могут стать недорогим и эффективным средством преобразования солнечного света. MFC на основе гетеротрофных микроорганизмов могут быть более перспективны в области очистки сточных вод и других экологических сферах. В настоящей статье приведен обзор новейших достижений в данной области и выделены нерешенные проблемы.
Библиография — 205 ссылок.
Biophotovoltaic solid state solar cells are new friendly environmentally solar cells inspired by photosynthesis phenomena. Photosystem I, a complex protein located in the chloroplast of the plant leaves that has a principal role in light absorption, is the most common light absorber used in biophotovoltaic solid state solar cells. Low efficiency and low current density are the main challenges in this kind of solar cell. In the present study, to vacillate the motion of electrons and holes, we use carbon nanotubes and tyrosine as transfer layers and to increase light absorbance, a solution of photosystem I with silver nanoparticles as an absorber layer is used. We show that the short circuit current density and the efficiency can be enhanced to 6.61 mA/cm ² and 0.83%, respectively which are the highest values for current density and efficiency reported for this kind of solar cell. These enhancements are due to the high electrical conductivity of carbon nanotubes, proper porosity of tyrosine and the localized surface plasmon resonance (LSPR) of silver nanoparticles induced under light irradiation. Our results can illuminate hopes and dreams for biophotovoltaic solid state solar cells with higher current density and higher efficiency.
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Nitrogen heterocyclic organics are promising hydrogen storage carriers with the advantage of being capable of large-scale transportation over long distances using existing oil and gas facilities. However, traditional methods for the hydrogenation and dehydrogenation of organic hydrogen carriers usually require high temperature and pressure conditions and external hydrogen supplies, which hinder their large-scale applications, as well as having certain safety risks. In this paper, a reversible electrochemical hydrogen storage system using quinoxaline as a hydrogen carrier was developed with potential for use at room temperature and atmospheric pressure. Experiments revealed that the hydrogenation conversion of quinoxaline reached 95% within 120 min at −0.20 V vs. RHE, and the dehydrogenation conversion of 1,2,3,4-tetrahydroquinoxaline reached 100% within 30 min at 1.30 V vs. RHE. This means that the system achieved quick and efficient reversible hydrogen storage. The Pd/NF dual-function electrode prepared by spontaneous redox reaction still showed high catalytic activity after 8 cycles, indicating its good long-term stability. The proton donor in the electrochemical hydrogenation process of quinoxaline was water, which completely eliminates the safety risk from the use of external hydrogen. This work provides a simple and reliable strategy for efficient hydrogen storage using nitrogen heterocyclic organics.
In this study, photobioelectrodes based on a ferredoxin-modified photosystem I (PSI-Fd) from Thermosynechococcus vestitus have been prepared and characterized regarding the direct electron transfer between PSI-Fd and the electrode. The modified PSI with the covalently linked ferredoxin (Fd) on its stromal side has been immobilized on indium-tin-oxide (ITO) electrodes with a 3-dimensional inverse-opal structure. Compared to native PSI, a lower photocurrent and a lower onset potential of the cathodic photocurrent have been observed. This can be mainly attributed to a different adsorption behavior of the PSI-Fd-construct onto the 3D ITO. However, the overall behavior is rather similar to PSI. First experiments have been performed for applying this PSI-Fd photobioelectrode for enzyme-driven NADPH generation. By coupling the electrode system with ferredoxin-NADP+-reductase (FNR), first hints for the usage of photoelectrons for biosynthesis have been collected by verifying NADPH generation.
Photosynthetic organisms like plants, algae, and cyanobacteria use light for the regeneration of dihydronicotinamide dinucleotide phosphate (NADPH). The process starts with the light‐driven oxidation of water by photosystem II (PSII) and the released electrons are transferred via the cytochrome b6f complex towards photosystem I (PSI). This membrane protein complex is responsible for the light‐driven reduction of the soluble electron mediator ferredoxin (Fd), which passes the electrons to ferredoxin NADP⁺ reductase (FNR). Finally, NADPH is regenerated by FNR at the end of the electron transfer chain. In this study, we established a clickable fusion system for in vitro NADPH regeneration with PSI−Fd and PSI−Fd−FNR, respectively. For this, we fused immunity protein 7 (Im7) to the C‐terminus of the PSI−PsaE subunit in the cyanobacterium Synechocystis sp. PCC 6803. Furthermore, colicin DNase E7 (E7) fusion chimeras of Fd and FNR with varying linker domains were expressed in Escherichia coli. Isolated Im7−PSI was coupled with the E7−Fd or E7−Fd−FNR fusion proteins through high‐affinity binding of the E7/Im7 protein pair. The corresponding complexes were tested for NADPH regeneration capacity in comparison to the free protein systems demonstrating the general applicability of the strategy.
Perovskite solar cells (PSCs) are one of the most environmentally renewable technologies for the next generation energy-harvesting devices. The motivation for PSCs as next-generation solar cells stems from their simple...
One restriction for biohybrid photovoltaics is the limited conversion of green light by most natural photoactive components. The present study aims to fill the green gap of photosystem I (PSI) with covalently linked fluorophores, ATTO 590 and ATTO 532. Photobiocathodes are prepared by combining a 20 μm thick 3D indium tin oxide (ITO) structure with these constructs to enhance the photocurrent density compared to setups based on native PSI. To this end, two electron transfer mechanisms, with and without a mediator, are studied to evaluate differences in the behavior of the constructs. Wavelength-dependent measurements confirm the influence of the additional fluorophores on the photocurrent. The performance is significantly increased for all modifications compared to native PSI when cytochrome c is present as a redox-mediator. The photocurrent almost doubles from -32.5 to up to -60.9 μA cm-2. For mediator-less photobiocathodes, interestingly, drastic differences appear between the constructs made with various dyes. While the turnover frequency (TOF) is doubled to 10 e-/PSI/s for PSI-ATTO590 on the 3D ITO compared to the reference specimen, the photocurrents are slightly smaller since the PSI-ATTO590 coverage is low. In contrast, the PSI-ATTO532 construct performs exceptionally well. The TOF increases to 31 e-/PSI/s, and a photocurrent of -47.0 μA cm-2 is obtained. This current is a factor of 6 better than the reference made with native PSI in direct electron transfer mode and sets a new record for mediator-free photobioelectrodes combining 3D electrode structures and light-converting biocomponents.
It is shown that in the chloroplast periodic structure with a defect, the resonant absorption of light can be implemented. It is found that the resonant light absorption depends significantly on the position of a defect. In terms of the absorption of light energy, an asymmetric resonator is more efficient than a symmetric one.
Bio‐hybrid solar cells, which are inspired by photosynthesis process in plants, are new low‐cost and environmentally friendly solar cells. In this kind of solar cells, photosystem I (PSI), which is the main part of photosynthesis process, is used as active layer and works as light absorber. In the present study, we extracted PSI from some easily accessible plants including spinach, Tung‐Oh, chye sim, local endive, beet greens, leek, Swiss chard and romaine lettuce and studied their light absorbance properties. We showed that the optical band gap of PSI extracted from all of these plants is about 1.8 eV which indicates the potential of these plants for using in bio‐hybrid solar cells. It was shown that, due to the higher light absorbance, spinach is the best plant for this kind of solar cells. Also, the effect of temperature on light absorbance of PSI extracted from spinach was investigated and showed that the light absorbance of PSI considerably decreases in high temperature values such as 80°C. Furthermore, we studied alkaline and acidic environments on PSI light absorbance and showed that the alkaline pH stress has no destructive effect on light absorbance, while the acidic pH stress causes a considerable decrease in light absorbance which is important in bio‐hybrid solar cell fabrication. This article is protected by copyright. All rights reserved.
The light from the Sun is a non-vanishing renewable source of energy which is free from environmental pollution and noise. It can easily compensate the energy drawn from the non-renewable sources of energy such as fossil fuels and petroleum deposits inside the earth. The fabrication of solar cells has passed through a large number of improvement steps from one generation to another. Silicon based solar cells were the first generation solar cells grown on Si wafers, mainly single crystals. Further development to thin films, dye sensitized solar cells and organic solar cells enhanced the cell efficiency. The development is basically hindered by the cost and efficiency. In order to choose the right solar cell for a specific geographic location, we are required to understand fundamental mechanisms and functions of several solar technologies that are widely studied. In this article, we have reviewed a progressive development in the solar cell research from one generation to other, and discussed about their future trends and aspects. The article also tries to emphasize the various practices and methods to promote the benefits of solar energy.
It is increasing clear that biofuels can be a viable source of renewable energy in contrast to the finite nature, geopolitical instability, and deleterious global effects of fossil fuel energy. Collectively, biofuels include any energy-enriched chemicals generated directly through the biological processes or derived from the chemical conversion from biomass of prior living organisms. Predominantly, biofuels are produced from photosynthetic organisms such as photosynthetic bacteria, micro- and macro-algae and vascular land plants. The primary products of biofuel may be in a gas, liquid, or solid form. These products can be further converted by biochemical, physical, and thermochemical methods. Biofuels can be classified into two categories: primary and secondary biofuels. The primary biofuels are directly produced from burning woody or cellulosic plant material and dry animal waste. The secondary biofuels can be classified into three generations that are each indirectly generated from plant and animal material. The first generation of biofuels is ethanol derived from food crops rich in starch or biodiesel taken from waste animal fats such as cooking grease. The second generation is bioethanol derived from non-food cellulosic biomass and biodiesel taken from oil-rich plant seed such as soybean or jatropha. The third generation is the biofuels generated from cyanobacterial, microalgae and other microbes, which is the most promising approach to meet the global energy demands. In this review, we present the recent progresses including challenges and opportunities in microbial biofuels production as well as the potential applications of microalgae as a platform of biomass production. Future research endeavors in biofuel production should be placed on the search of novel biofuel production species, optimization and improvement of culture conditions, genetic engineering of biofuel-producing species, complete understanding of the biofuel production mechanisms, and effective techniques for mass cultivation of microorganisms.
The design of electrochemical solar cells (SCs), including those composed of biological pigments is an actively developing direction of obtaining alternative energy. SCs were studied under different temperatures, light intensities and spectral conditions. Furthermore, to understand processes occurring in the SCs, investigations characterizing the efficiency and stability with regard to environmental factors are also required. For this aim, novel instrumentation for the investigation of environmental effects on photocurrent generated by SCs has been designed and constructed. The system can be a model, which reflects conditions required for effective and stable functioning of the solar cells. Preliminary results are shown for two types of solar cells with two photosensitizers: thylakoid membrane preparations and anthocyanin-enriched raspberry extracts. It was shown that electrogenic activity decreased by a half at 40 °C and returned back to the initial value under gradual cooling. Maximum current obtained from the thylakoid-based SC was 0.46 μA, while maximum current generated by the anthocyanin-based SC was 1.75 μA. The goal of this investigation is to find new ways to increase efficiency and stability of bio-based SCs. In future, this measuring system can be used for investigation of solar cells based on long-wave forms of chlorophylls (Chls d and f) and components of the photosynthetic apparatus comprising these chlorophylls.
Biofuels are the promising alternative to exhaustible, environmentally unsafe fossil fuels. Algal biomass is attractive raw for biofuel production. Its cultivation does not compete for cropland with agricultural growing of food crop for biofuel and does not require complex treatment methods in comparison with lignocellulose-enriched biomass. Many microalgae are mixotrophs, so they can be used as energy source and as sewage purifier simultaneously. One of the main steps for algal biofuel fabrication is the cultivation of biomass. Photobioreactors and open-air systems are used for this purpose. The formers allow the careful cultivation control, but the latter ones are cheaper and simpler. Biomass conversion processes may be divided to the thermochemical, chemical, biochemical methods and direct combustion. For biodiesel production, triglyceride-enriched biomass undergoes transetherification. For bioalcohol production, biomass is subjected to fermentation. There are three methods of biohydrogen production in the microalgal cells: direct biophotolysis, indirect biophotolysis, fermentation.
Oxygenic photosynthesis is a process of light energy conversion into the chemical
energy using water and carbon dioxide. The efficiency of energy conversion in the
primary processes of photosynthesis is close to 100%. Therefore, for many years,
photosynthesis has attracted the attention of researchers as the most efficient and ecofriendly
pathway of solar energy conversion for alternative energy systems. The recent
advances in the design of optimal solar cells include the creation of converters, in which
thylakoid membranes, photosystems and whole cells of cyanobacteria immobilized on
nanostructured electrode are used. As the mechanism of solar energy conversion in
photosynthesis is sustainable and environmentally safe, it has a great potential as an
example of renewable energy device. Application of pigments such as Chl f and Chl d
will extend the spectral diapason of light transforming systems allow to absorb the farred
and near infra-red photons of the spectrum (in the range 700-750 nm). This article
presents the recent achievements and challenges in the area of solar cells based on
photosynthetic systems.
The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Qy) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria.
We have investigated the nature of the photocurrent generated by Photosystem II (PSII), the water oxidizing enzyme, isolated from Thermosynechococcus elongatus, when immobilized on nanostructured titanium dioxide on an indium tin oxide electrode (TiO2/ITO). We investigated the properties of the photocurrent from PSII when immobilized as a monolayer versus multilayers, in the presence and absence of an inhibitor that binds to the site of the exchangeable quinone (QB) and in the presence and absence of exogenous mobile electron carriers (mediators). The findings indicate that electron transfer occurs from the first quinone (QA) directly to the electrode surface but that the electron transfer through the nanostructured metal oxide is the rate-limiting step. Redox mediators enhance the photocurrent by taking electrons from the nanostructured semiconductor surface to the ITO electrode surface not from PSII. This is demonstrated by photocurrent enhancement using a mediator incapable of accepting electrons from PSII. This model for electron transfer also explains anomalies reported in the literature using similar and related systems. The slow rate of the electron transfer step in the TiO2 is due to the energy level of electron injection into the semiconducting material being below the conduction band. This limits the usefulness of the present hybrid electrode. Strategies to overcome this kinetic limitation are discussed.
The thylakoid membrane mainly consists of photosystem I (PSI), photosystem II (PSII) and the cytochrome b6f embedded in a lipid bilayer. PSI and PSII have the ability to capture sunlight and create an electron-hole pair. The study aims at utilizing these properties by using the thylakoid membrane to construct a photo-electrochemical cell. A controlled aerosol technique, electrohydrodynamic atomization, allows a systematic study by the fabrication of different cell configurations based on the surfactant concentration without any linker, sacrificial electron donor and mediator. The maximum photocurrent density observed is 6.7 mA cm(-2) under UV and visible light, and 12 μA cm(-2) under visible light illumination. The electron transfer occurs from PSII to PSI via cytochrome b6f and the electron at PSII is regenerated by water oxidation, similar to the z-scheme of photosynthesis. This work shows that re-engineering the natural photosynthesis circuit by the novel technique of electrospray deposition can result in an environmentally friendly method of harvesting sunlight.
Photosynthesis is a process which converts light energy into energy contained in the chemical bonds of organic compounds by photosynthetic pigments such as chlorophyll (Chl a, b, c, d, f) or bacteriochlorophyll. It occurs in phototrophic organisms, which include higher plants and many types of photosynthetic bacteria, including cyanobacteria. In the case of the oxygenic photosynthesis, water is a donor of both electrons and protons, and solar radiation serves as inexhaustible source of energy. Efficiency of energy conversion in the primary processes of photosynthesis is close to 100%. Therefore, for many years photosynthesis has attracted the attention of researchers and designers looking for alternative energy systems as one of the most efficient and eco-friendly pathways of energy conversion. The latest advances in the design of optimal solar cells include the creation of converters based on thylakoid membranes, photosystems, and whole cells of cyanobacteria immobilized on nanostructured electrode (gold nanoparticles, carbon nanotubes, nanoparticles of ZnO and TiO2). The mode of solar energy conversion in photosynthesis has a great potential as a source of renewable energy while it is sustainable and environmentally safety as well. Application of pigments such as Chl f and Chl d (unlike Chl a and Chl b), by absorbing the far red and near infrared region of the spectrum (in the range 700-750 nm), will allow to increase the efficiency of such light transforming systems. This review article presents the last achievements in the field of energy photoconverters based on photosynthetic systems.
Conventional DSSCs comprise semi-conducting anodes sensitized with complex synthetic organometallic dyes, a platinum counter anode, and a liquid electrolyte. This work focuses on replacing synthetic dyes with a naturally occurring biological pigment-protein complex known as photosystem I (PSI). Specifically, ZnO binding peptides (ZOBiP) fused PSI subunits (ZOBiP-PsaD and ZOBiP-PsaE) and TiO2 binding peptides (TOBiP) fused ferredoxin (TOBiP-Fd) have been produced recombinantly from E. coli. The MOBiP-fused peptides been characterized via Western blotting, circular dichroism, MALDI-TOF, and cyclic voltammetry. ZOBiP-PSI subunits have been used to replace wild-type PsaD and PsaE at efficiencies up to 90%, and TOBiP-Fd has been chemical-ly cross-linked to the stromal hump of PSI. These MOBiP-peptides and MOBiP-PSI complexes have been produced and incubated with various metal-oxide nanoparticles, showing an increased binding when compared to wild type PSI complexes.
The replacement of oxide semiconducting TiO2 nano particles with one dimensional TiO2 nanotubes (TNTs) has been used for improving the electron transport in the dye-sensitized solar cells (DSSCs). Although use of one dimensional structure provides the enhanced photoelectrical performance, it tends to reduce the adsorption of dye on the TiO2 surface due to decrease of surface area. To overcome this problem, we investigate the effects of TiCl4 treatment on DSSCs which were constructed with composite films made of TiO2 nanoparticles and TNTs. To find optimum condition of TNTs concentration in TiO2 composites film, series of DSSCs with different TNTs concentration were made. In this optimum condition (DSSCs with 10 wt% of TNT), the effects of post treatment are compared for different TiCl4 concentrations. The results show that the DSSCs using a TiCl4 (90 mM) post treatment shows a maximum conversion efficiency of 7.83% due to effective electron transport and enhanced adsorption of dye on TiO2 surface.
Nowadays, dye-sensitized solar cells (DSSCs) are the most extensively investigated systems for the conversion of solar energy into electricity, particularly for implementation in devices where low cost and good performance are required. Nevertheless, a key aspect is still to be addressed, being considered strongly harmful for a long time, which is the presence of water in the cell, either in the electrolyte or at the electrode/electrolyte interface. Here comes the present review, in the course of which we try our best to address the highly topical role of water in DSSCs, trying to figure out if it is a poisoner or the keyword to success, by means of a thoroughly detailed analysis of all the established phenomena in an aqueous environment. Actually, in the last few years the scientific community has suddenly turned its efforts in the direction of using water as a solvent, as demonstrated by the amount of research articles being published in the literature. Indeed, by means of DSSCs fabricated with water-based electrolytes, reduced costs, non-flammability, reduced volatility and improved environmental compatibility could be easily achieved. As a result, an increasing number of novel electrodes, dyes and electrolyte components are continuously proposed, being highly challenging from the materials science viewpoint and with the golden thread of producing truly water-based DSSCs. If the initial purpose of DSSCs was the construction of an artificial photosynthetic system able to convert solar light into electricity, the use of water as the key component may represent a great step forward towards their widespread diffusion in the market.
Global energy demand is increasing rapidly and due to intensive consumption of different forms of fuels, there is increasing concerns over the reduction in readily available conventional energy resources. Because of the deleterious atmospheric effects of fossil fuels and the uncertainties of future energy supplies, there is a surge of interest to find environmentally friendly alternative energy sources. Hydrogen (H2) has attracted worldwide attention as a secondary energy carrier, since it is the lightest carbon neutral fuel rich in energy per unit mass and easy to store. Several methods and technologies have been developed for H2 production, but none of them are able to replace the traditional combustion fuel used in automobiles so far. Extensively modified and renovated methods and technologies are required to introduce H2 as an alternative efficient, clean, and cost effective future fuel. Among several emerging renewable energy technologies, photobiological H2 production by oxygenic photosynthetic microbes such as green algae and cyanobacteria or by artificial photosynthesis has attracted significant interest. In this short review, we summarize the recent progresses and challenges in H2-based energy production by means of biological and artificial photosynthesis routes.
The macromolecular pigment-protein complex has the merit of high efficiency for light-energy capture and transfer after long-term photosynthetic evolution. Here bio-dyes of A.
platensis photosystem I (PSI) and spinach light-harvesting complex II (LHCII) are spontaneously sensitized on three types of designed TiO2 films, to assess the effects of pigment-protein complex on the performance of bio-dye sensitized solar cells (SSC). Adsorption models of bio-dyes are proposed based on the 3D structures of PSI and LHCII, and the size of particles and inner pores in the TiO2 film. PSI shows its merit of high efficiency for captured energy transfer, charge separation and transfer in the electron transfer chain (ETC), and electron injection from FB to the TiO2 conducting band. After optimization, the best short current (JSC) and photoelectric conversion efficiency (η) of PSI-SSC and LHCII-SSC are 1.31 mA cm-2 and 0.47%, and 1.51 mA cm-2 and 0.52%, respectively. The potential for further improvement of this PSI based SSC is significant and could lead to better utilization of solar energy.
This work determines the effect of compact TiO2 layers that are deposited onto fluorine-doped tin oxide (FTO), to improve the performance of dye-sensitized solar cells (DSSC). A series of compact TiO2 layers are prepared using radio frequency (rf) reactive magnetron sputtering. The films are characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The results show that when the Ar/O2/N2 flow rates are 36: 18: 9, the photo-induced decomposition of methylene blue and photo-induced hydrophilicity are enhanced. After annealing at 450°C in an atmosphere ambient for 30 min, the compact TiO2 layers exhibit higher optical transmittance. The XRD patterns for the TiO2 films for FTO/glass show a good crystalline structure and anatase (101) diffraction peaks, which demonstrate a higher crystallinity than the ITO/glass films. As a result of this increase in the short circuit photocurrent density, the open-circuit photovoltage, and the fill factor, the DSSC with the FTO/glass and Pt counter electrode demonstrates a solar conversion efficiency of 7.65%.
Solar energy can be harvested either by deriving directly from sunlight or by indirect methods. A variety of technologies have been developed to harness solar energy. Among them, utilisation of solar energy by solar cell is an important and effective method and has a high potential in the commercial market. Based on the techniques and materials used to fabricate solar cell, the solar cells are classified into three generations. First generation solar cells are the larger, silicon based photovoltaic cells. The disadvantages of these solar cells are limited availability of silicon, requires expensive manufacturing technologies and higher energy photons are wasted as heat. The second generation solar cells are called thin film solar cells, which are significantly cheaper than previous generation cells but have lower efficiencies. The third generation solar cells are still in the research phase, but the results are promising and encouraging. Generally, third generation cells include nanocrystalline solar cells and dye sensitised solar cells, they do not have the p-n junction as in traditional solar cells. Third generation solar cells provide a technically and economically credible alternative concept to present day p-n junction solar cells. In the present study, the technology of the dye sensitised solar cell is introduced with a short description about the operating principle of the cell. After this, a more detailed study is carried out about the dye sensitised solar cell, taking into account the key steps involved in photovoltaic energy conversion and also the other important fundamental operational aspects of the solar cell physics and chemistry.
Photosynthesis is one of the first natural processes evolved by cyanobacteria, algae and green plants to trap light and CO2 in the form of reduced carbon compounds while simultaneously oxidizing water to oxygen. The photosynthetic energy conversion forms the basis for all the existing life today. The photosynthetic energy is being harnessed in many ways using modern technologies for the production of fuels using photosynthetic organisms, generation of direct electricity using photosystems/photosynthetic organisms in photo-bioelectrochemical cells or through photovoltaic systems. While the production of energy rich carbon fuels (ethanol, propanol) from photosynthetic organisms has already been accomplished due to advancement in understanding microbial physiology and metabolism, the photosynthetic hydrogen production as well as direct electricity generation from light is still at its infancy. Recent advances include combining photosystem complexes with hydrogenases for hydrogen production, using isolated thylakoids, photosystems on nanostructured electrodes such as gold nanoparticles, carbon nanotubes, ZnO nanoparticles for electricity generation. Many challenging optimizations on the immobilization methods, catalyst stability and isolation procedures, electron transfer strategies have acquired momentum leading to the production of more stable and higher current densities and power densities in photosynthetic devices. Further, the use of whole cell microorganisms (cyanobacteria, microalgae) rather than their isolated counterparts has produced promising results. The photosynthetic energy conversion has an enormous potential for renewable energy generation in a sustainable and environment friendly manner.
An improved protocol for measuring light-dependent proton translocation across the membrane of isolated
thylakoids is described. The method uses a pH electrode attached to data acquisition software to measure the pH increase in
the bathing solution as protons are pumped from the solution to the internal compartments of the thylakoid vesicles. Up to the
point of light saturation, the magnitude of proton movement depends on irradiance level. Proton translocation is inhibited in a
concentration-dependent manner in the presence of dichlorophenyl dimethyl urea (DCMU). In the presence of gramicidin D,
a proton gradient across the membrane can be neither established nor maintained. Depending on its redox state,
dichlorophenol indophenol (DCPIP) can act as an electron donor or acceptor to or from different components of the thylakoid
membrane. Studies using oxidized or reduced DCPIP with or without a high concentration of DCMU demonstrate that both
linear and cyclic electron flow both result in light-dependent proton translocation. Proton translocation is a fundamental
process used by most types of organisms to create a transmembrane proton gradient that provides the energy for ATP
synthesis. The value of the described method is that students can directly measure the disappearance of protons from the
thylakoid suspension solution and, by adding DCMU and oxidized or reduced DCPIP, demonstrate the coupling of electron
transport to proton translocation in the thylakoid membrane.
Plants and photosynthetic bacteria contain protein-molecular complexes that harvest photons with nearly optimum quantum yield and an expected power conversion efficiency exceeding 20%. In this work, we demonstrate the integration of electrically active photosynthetic protein-molecular complexes in solid-state devices, realizing photodetectors and photovoltaic cells with internal quantum efficiencies of approximately 12%. Electronic integration of devices is achieved by self-assembling an oriented monolayer of photosynthetic complexes, stabilizing them with surfactant peptides, and then coating them with a protective organic semiconductor.
The arrangement of core antenna complexes (B808-866-RC) in the cytoplasmic membrane of filamentous phototrophic bacterium Chloroflexus aurantiacus was studied by electron microscopy in cultures from different light conditions. A typical nearest-neighbor center-to-center distance of ~18 nm was found, implying less protein crowding compared to membranes of purple bacteria. A mean RC:chlorosome ratio of 11 was estimated for the occupancy of the membrane directly underneath each chlorosome, based on analysis of chlorosome dimensions and core complex distribution. Also presented are results of single-particle analysis of core complexes embedded in the native membrane.
Photosynthesis is responsible for the sunlight-powered conversion of carbon dioxide and water into chemical energy in the form of carbohydrates and the release of O2 as a by-product. Although many proteins are involved in photosynthesis, the fascinating machinery of Photosystem II (PSII) is at the heart of this process. This tutorial review describes an emerging technique named protein film photoelectrochemistry (PF-PEC), which allows for the light-dependent activity of PSII adsorbed onto an electrode surface to be studied. The technique is straightforward to use, does not require highly specialised and/or expensive equipment, is highly selective for the active fractions of the adsorbed enzyme, and requires a small amount of enzyme sample. The use of PF-PEC to study PSII can yield insights into its activity, stability, quantum yields, redox behaviour, and interfacial electron transfer pathways. It can also be used in PSII inhibition studies and chemical screening, which may prove useful in the development of biosensors. PSII PF-PEC cells also serve as proof-of-principle solar water oxidation systems; here, a comparison is made against PSII-inspired synthetic photocatalysts and materials for artificial photosynthesis.
Cyanobacteria possess unique and exciting features among photosynthetic microorganisms for energy conversion applications. This study focuses on production of direct electricity using a cyanobacterium called Nostoc sp. (NOS) as a photo-biocatalyst immobilized on carbon nanotubes on the anode of photo-bioelectrochemical cells. By illuminating with light (intensity 76 mW cm(-2)) the NOS immobilized on a carbon nanotube (CNT) modified electrode generated a photocurrent density of 30 mA m(-2) at 0.2 V (vs. Ag/AgCl). The contribution of different photosynthetic pigments in NOS to the light capture was analyzed and chlorophyll-a was found to be the major contributor to light capture followed by phycocyanin. Further investigation using a set of inhibitors revealed that the electrons were redirected predominantly from PSII to the CNT through the plastoquinone pool and quinol oxidase. A rudimentary design photosynthetic electrochemical cell has been constructed using NOS/CNT on the anode and laccase/CNT on the cathode as catalysts. The cell generated a maximum current density of 250 mA m(-2) and a peak power density of 35 mW m(-2) without any mediator. By the addition of 1,4-benzoquinone as a redox mediator, the electricity generation capability was significantly enhanced with a current density of 2300 mA m(-2) and a power density of 100 mW m(-2). The power densities achieved in this work are the highest among 'non-engineered' cyanobacteria based electrochemical systems reported to date.
Oxygenic photosynthesis is driven via sequential action of PSII and PSI reaction centers via the Z-scheme. Both of these pigment-membrane protein complexes are found in cyanobacteria, algae, and plants. Unlike PSII, PSI is remarkably stable and does not undergo limiting photo-damage. This stability, as well as other fundamental structural differences, makes PSI the most attractive reaction centers for applied photosynthetic applications. These applied applications exploit the efficient light harvesting and high quantum yield of PSI where the isolated PSI particles are redeployed providing electrons directly as a photocurrent or, via a coupled catalyst to yield H2. Recent advances in molecular genetics, synthetic biology, and nanotechnology have merged to allow PSI to be integrated into a myriad of biohybrid devices. In photocurrent producing devices, PSI has been immobilized onto various electrode substrates with a continuously evolving toolkit of strategies and novel reagents. However, these innovative yet highly variable designs make it difficult to identify the rate-limiting steps and/or components that function as bottlenecks in PSI-biohybrid devices. In this study we aim to highlight these recent advances with a focus on identifying the similarities and differences in electrode surfaces, immobilization/orientation strategies, and artificial redox mediators. Collectively this work has been able to maintain an annual increase in photocurrent density (A cm(-2)) of ~10-fold over the past decade. The potential drawbacks and attractive features of some of these schemes are also discussed with their feasibility on a large-scale. As an environmentally benign and renewable resource, PSI may provide a new sustainable source of bioenergy. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.
Z-Scheme on wires: The two photosystems of the natural photosynthetic Z-scheme have been connected by immobilizing them within redox hydrogels on individual electrodes. Upon irradiation, this biophotovoltaic device produced photocurrents as a closed and autonomous system. The open-circuit voltage of the cell corresponds to the potential difference between the two redox hydrogels and indicates the coupling of the two charge separation steps. © 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol
with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2
suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical
performance of TiO2 electrodes, cast as single layers, was dependent on the thermal
treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent
of residual organics and found that acetates from the TiO2 precursor preparation were retained
within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness
4 lm produced an energy conversion efficiency as high as 5.4% using this simple thermal
treatment.
Spinach thylakoids were immobilized onto multiwalled carbon nanotubes using a molecular tethering chemistry. The resulting thylakoid–carbon nanotube composites showed high photo-electrochemical activity under illumination. Multiple membrane proteins have been observed to participate in direct electron transfer with the electrode, resulting in the generation of photocurrents, the first of its kind reported for natural photosynthetic systems. Upon inclusion of a mediator, the photo-activity was enhanced. The major contributor to the photocurrent was the light-induced water oxidation reaction at the photosystem II complex. The thylakoid–MWNT composite electrode yielded a maximum current density of 68 μA cm−2 and a steady state current density of 38 μA cm−2, which are two orders of magnitude larger than previously reported for similar systems. The high electrochemical activity of the thylakoid–MWNT composites has significant implications for both photosynthetic energy conversion and photofuel production applications. A fuel cell type photosynthetic electrochemical cell developed using a thylakoid–MWNT composite anode and laccase cathode produced a maximum power density of 5.3 μW cm−2, comparable to that of enzymatic fuel cells. The carbon based nanostructured electrode has the potential to serve as an excellent immobilization support for photosynthetic electrochemistry based on the molecular tethering approach as demonstrated in this work.
Photosystem 1 (PS1) catalyzes the light driven translocation of electrons in the process of oxygenic photosynthesis. Isolated PS1 was immobilised on a goldelectrode surface via an Os complex containing redoxpolymer hydrogel which simultaneously is used as immobilisation matrix and as electron donor for PS1. On addition of methyl viologen as sacrificial electron acceptor, a catalytic photocurrent with densities of up to 29 μA cm−2 at a light intensity of 1.8 mW cm−2 was observed upon illumination—equivalent to an incident photon to carrier efficiency (IPCE) of 3.1%. The strong dependence of the catalytic reaction on the light intensity and the dissolved oxygen concentration indicates that a significant photocurrent from excited PS1 to the electrode can only be realized in the presence of oxygen.
The Sun provides about 100,000 Terawatts (TW) to the Earth, which is approximately ten thousand times greater than the world’s present rate of energy consumption (14 TW). Photovoltaic (PV) cells are being used increasingly to tap into this huge resource and will play a key role in future sustainable energy systems. Indeed, our present needs could be met by covering 0.5% of the Earth’s surface with PV installations that achieve a conversion efficiency of 10%. Fig. 8.1 shows a simple diagram of how a conventional photovoltaic device works. The top and bottom layers are made of an n-doped and p-doped silicon, where the charge of the mobile carriers is negative (electrons) or positive (holes), respectively. The p-doped silicon is made by ‘doping’ traces of an electron-poor element such as gallium into pure silicon, whereas n-doped silicon is made by doping with an electron-rich element such as phosphorus. When the two materials contact each other spontaneous electron and hole transfer across the junction produces an excess positive charge on the side of the n-doped silicon (A) and an excess negative charge on the opposite p-doped (B) side. The resulting electric field plays a vital role in the photovoltaic energy conversion process. Absorption of sunlight generates electron-hole pairs by promoting electrons from the valence band to the conduction band of the silicon. Electrons are minority carriers in the p-type silicon while holes are minority carriers in the n-type material. Their lifetime is very short as they recombine within microseconds with the oppositely charged majority carriers. The electric field helps to collect the photo-induced carriers because it attracts the minority carriers across the junction as indicated by the arrows in Fig. 8.1, generating a net photocurrent. As there is no photocurrent flowing in the absence of a field, the maximum photo-voltage that can be attained by the device equals the potential difference that is set up in the dark at the p-n junction. For silicon this is about 0.7V. So far, solid-state junction devices based on crystalline or amorphous silicon (Si) have dominated photovoltaic solar energy converters, with 94% of the market share.
Micron sized titania flakes with thickness about 40nm were used in the titania pastes to assemble dye-sensitized solar cells (DSSCs). Using the same deposition method, better particle dispersion of titania flakes resulted in well bonded and integral films comparing to cracking of Degussa P25 nanoparticle films during the evaporation and sintering processes. There are two features of titania flakes which leads to improved conversion efficiency of DSSC: (1) Higher and stronger adsorption of N-719 dyes due to high specific surface area (2) Stronger light scattering of visible light spectrum because of micron scale wide in two dimensions of the flakes. The thickness of the conducting TiO2 was critical to the IV characteristics of DSSC such as the short-circuit current density (Isc) and open-circuit voltage (Voc). Under the same thickness basis, calcined titania flakes provided 5 times higher efficiency than the photoelectrodes consisted of Degussa P25 nanoparticles (7.4% vs. 1.2%).
Photosystem II (PSII) modified gold electrodes were prepared by the deposition of PSII reconstituted with platinum nanoparticles (PtNPs) on Au electrodes. PtNPs modified with 1-[15-(3,5,6-trimethyl-1,4-benzoquinone-2-yl)]pentadecyl disulfide ((TMQ(CH2)15S)2) were incorporated into the QB site of PSII isolated from the thermophilic cyanobacterium, Thermosynechococcus elongatus. The reconstitution was confirmed by QA-reoxidation measurements. PSII reconstituted with PtNPs was deposited and integrated on a Au(111) surface modified with 4,4'-biphenyldithiol. The cross-section of the reconstituted PSII film on the Au electrode was investigated by SEM. Absorption spectra showed that the surface coverage of electrode was about 18 pmol PSII cm-2. A photocurrent density of 15 nAcm-2 at E = +0.10 V (vs. Ag/AgCl) was observed under 680 nm irradiation. The photoresponse showed good reversibility under alternating light and dark conditions. Clear photoresponses were not observed in the absence of PSII and molecular wire. These results supported the photocurrent originated from PSII and moved to gold electrode by light irradiation, which also confirmed conjugation with orientation through molecular wire.
Dye-sensitized solar cells (DSSCs) feature low cost, stability, and environment friendliness and are thus a promising substitute for traditional silicon solar cells. DSSCs have received intensive research attention and have been rapidly developing in the last two decades. The efficiency of DSSCs should be increased to promote their commercialization and large-scale application. This brief review summarizes the major progress in advanced nano/micromaterials to improve photoanodes and enhance the conversion efficiencies of DSSCs. Commonly used methods to improve photoanodes include semiconductor film nanoarchitecture, light-scattering material application, compositing, doping, interfacial engineering, and TiCl4 post-treatment. This review provides insights into DSSC improvement and development of other photovoltaics, such as perovskite solar cells and photoelectrochemical cells.
Hierarchical TiO2 submicrorods (HTRs) assembled from tiny nanoparticles and nanorods were synthesized through a facile hydrothermal method using titanate glycolate rods as a self-template. The as-prepared hierarchical TiO2 submicrorods possessed a higher surface area (103 m² g⁻¹) than P25 nanoparticles (NPs) (55 m² g⁻¹). Composite photoanodes in dye-sensitized solar cells (DSSCs) were prepared by integrating the prepared HTRs and P25 NPs, and a photovoltaic conversion efficiency of 8.09% was obtained, which was obviously higher than that of the pristine P25 NPs-based photoanode (5.37%). The incorporated hierarchical TiO2 submicrorods in the hybrid photoanode film showed three functions in the enhancing photovoltaic performance of DSSCs: (i) increasing the specific surface area for effective adsorption of dye molecules, (ii) enhancing the light harvesting efficiency, and (iii) accelerating the electron transport by the films. This work highlights the importance of tuning the structure of the photoanode and exhibits an efficient strategy for enhanced energy conversion of DSSCs.
The fabrication of artificial photosynthetic systems to convert solar energy into electrical power is of great importance to meet human needs for energy; photosystem II (PSII), the core enzyme for water splitting in natural solar energy conversion processes can be introduced for this purpose. However, there remain significant challenges in the facile preparation of such semi-artificial photoanode systems with enhanced photocurrent responses. Herein we report a hybrid photoanode system consisting of PSII from spinach integrated into an indium-tin oxide electrode modified with nanotubular titania that is synthesized by using cellulose paper as a scaffold. This electrode provides a well-defined hierarchical nanostructure for protein loading, and the fine titania nanocrystals facilitate electron transfer from PSII to the electrode. The resulting semiconductor-protein hybrid photo-bioelectrochemical system enhances direct electron transfer (1.3 μA cm⁻²) and mediated electron transfer (10.6 μA cm⁻²) photocurrents.
The dye-sensitized solar cell (DSSC) using visible and near-infrared sensitization of nanocrystalline TiO2 films using a series of four aluminum phthalocyanines was developed and its photoelectrochemical properties were investigated. By using aluminum 2,9,16,23-tetrakis(phenyl-thio)-29H,31H-phthalocyanine chloride adsorbed on a nanocrystalline TiO2 film electrode, the I-SC, V-OC, FF, P-max and eta values were largest compared with the other DSSCs using aluminum phthalocyanines. For all the DSSCs using aluminum phthalocyanines, IPCE values at near-infrared region (700 nm) are larger than those at visible region (500 nm). Thus, the DSSC using near-infrared sensitization of nanocrystalline TiO2 film by aluminum phthalocyanines was developed. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines.
All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn-Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25-90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn-Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn complexes decomposing to Mn oxide. We then provide a detailed assessment of the chemistry of Mn oxides by considering how their bulk and nanoscale properties contribute to their effectiveness as water-oxidizing catalysts.
Light-harvesting antennas are pigment-proteins that absorb light energy and transfer it to photosynthetic reaction centers. This chapter starts with a brief non-technical explanation of how antennas harvest light. The antennas of the five divisions of photosynthetic bacteria (including cyanobacteria) are introduced; the antennas are placed in the context of their photosynthetic membranes. The evolutionary origin of chloroplasts by primary and secondary endosymbiosis is explained. A brief description of the various algal groups is followed by a more detailed discussion of the higher plant chloroplast and the roles of the LHC superfamily antennas. Throughout, readers are directed to the relevant chapters in the book where detailed information can be found.
Novel Photosystem I (PSI) based solid-state solar cells were prepared by directly electropolymerizing polyaniline (PAni) in the presence of solubilized PSI on a TiO2 anode. These devices feature a unique bio-derived, photoactive composite layer for efficient charge separation and charge transfer from protein to electrode. This work introduces a new artificial photosynthesis platform for scalable and sustainable solar energy conversion.
Photosynthesis is one of the most important processes on our planet, providing food and oxygen for the majority of living organisms on Earth. Over the past 30 years scientists have made great strides in understanding the central photosynthetic process of oxygenic photosynthesis, whereby water is used to provide the hydrogen and reducing equivalents vital to CO2 reduction and sugar formation. A recent crystal structure at 1.9-1.95Å has made possible an unparalleled map of the structure of photosystem II (PSII) and particularly the manganese-calcium (Mn-Ca) cluster, which is responsible for splitting water. Here we review how knowledge of the water-splitting site provides important criteria for the design of artificial Mn-based water-oxidizing catalysts, allowing the development of clean and sustainable solar energy technologies.
Copyright © 2015 Elsevier Ltd. All rights reserved.
We here show that an effective blocking layer for dye-sensitized solar cells (DSSCs) can be formed by spin coating a commercial TiO2 paste onto a conducting glass substrate. The spin-coated TiO2 layer was made more compact than the main absorption layer by TiCl4 treatment. DSSCs employing a compact layer exhibited an average current density and an efficiency of 19.09 mA/cm2 and 9.10%, respectively, while 16.91 mA/cm2 and 8.33% were obtained from unblocked reference cells. The enhanced DSSC performance is attributed to the increased electron lifetime. Intensity-modulated photovoltage spectroscopy and open-circuit voltage decay analysis showed that a TiCl4-treated compact layer substantially suppresses the charge recombination at the TiO2/substrate interface, thereby increasing the electron lifetime.
Ultrathin anatase TiO2 films were coated on the fluorine-doped tin oxide (FTO) glass by anodic electrodeposition followed by annealing at 450 degrees C before the formation of thick TiO2 layer. The electrodeposited TiO2 films were more compact structure near the FTO surface (inner layer), and became less compact further away from the surface (outer layer). The outer layer of film deposited at 10 mu A cm(-2) was composed of granular nanoparticles and that of film deposited at 5 mu A cm(-2) was composed of short nanorods. The inner compact layer could act as a blocking layer to suppress the charge recombination. The outer loose layer could provide an anchoring layer for a better electrical contact between FTO and thick TiO2 layer. The photoelectron conversion efficiency (eta) of dye-sensitized solar cell (DSC) using TiO2-coated FTO deposited at 10 mu A cm(-2) was 6.9%, which is higher than that of DSC using bare FTO (6.5%). The outer anchoring layer composed of short nanorods deposited at 5 mu A cm(-2) could significantly reduce the interfacial contact resistance between FTO and main TiO2 layer .Therefore, eta of DSC was further increased to 7.1% after employing the TiO2-coated FTO deposited at 5 mu A cm(-2). (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.061201jes]
Photo-bioelectrochemical cells are devices that use biomolecule-modified electrodes for the conversion of solar light to electrical power. We present the construction of a layered assembly of the native photosynthetic reaction centers photosystem I (PSI) and photosystem II (PSII), crosslinked by polyvinyl pyridine/methyl pyridinium and cytochrome c (Cyt. c) that act as an electron transfer mediating layer. Electrostatic interactions and glutaric dialdehyde crosslinking of the protein layers stabilize the biomolecules on the electrodes. The irradiation of the PSII/Cyt. c/PSI-modified electrodes facilitates an electron transfer cascade, where photoexcited PSII leads to O2 evolution and to the reduction of Cyt. c, with the concomitant ejection of electrons from PSI to the electrode, and the reduction of the P700+ sites by the reduced Cyt. c units.
Photosystem I (PSI) from oxygenic photosynthetic organisms is an attractive sensitizer for nano-biohybrid solar cells as it has a combined light-harvesting and reaction center in one protein complex; and operates at a quantum yield close to one in biological systems. Using a linker-free deposition technique enabled by an electrospray system, PSI was coupled to 1-D nano-structured titanium dioxide thin films to fabricate an electrode for a photo-electrochemical cell. After deposition, the surfactant in the PSI aggregate was dissolved in the surfactant-free electrolyte; ensuring that partly hydrophobic PSI was not resuspended and stayed in contact with titanium dioxide. A maximum current density of 4.15 mA cm(-2) was measured after 10 minutes of electrospray deposition, and this is the highest current density reported so far for PSI-based photoelectrochemical cells. The high current is attributed to 1D nano-structure of titanium dioxide and orientation of the PSI onto the surface, which allows easy transfer of electrons.
The dye-sensitized solar cell (DSSC) using visible and near-infrared sensitization of nanocrystalline TiO2 films using a series of four aluminum phthalocyanines was developed and its photoelectrochemical properties were investigated. By using aluminum 2,9,16,23-tetrakis(phenyl-thio)-29H,31H-phthalocyanine chloride adsorbed on a nanocrystalline TiO2 film electrode, the ISC, VOC, FF, Pmax and η values were largest compared with the other DSSCs using aluminum phthalocyanines. For all the DSSCs using aluminum phthalocyanines, IPCE values at near-infrared region (700 nm) are larger than those at visible region (500 nm). Thus, the DSSC using near-infrared sensitization of nanocrystalline TiO2 film by aluminum phthalocyanines was developed.
An electrical model of the dye-sensitized solar cell (DSC) is presented, which relates material parameters to cell performance. Based on these parameters, the model permits the calculation of steady-state properties as e.g. internal currents or particle densities and the complete I–V characteristic of a DSC. The cell is modelled as a pseudo-homogeneous effective medium, consisting of the nanoporous TiO2 semiconductor, the light-absorbing dye and the redox electrolyte, which are intermixed. Continuity and transport equations are applied to all the charge carriers involved: the electrons in the TiO2 conduction band, and the iodide, triiodide and cations of the electrolyte. The macroscopic electric field, resulting from the unbalanced charge-carrier distribution under illumination, is calculated using Poisson's equation. The front and back cell boundaries are modelled as an ohmic metal–semiconductor contact and as a redox electrode via a current-overpotential equation, respectively. One of the main simplifications of this model is the consideration of only one-electron loss mechanism: the relaxation from the TiO2 conduction band to the redox electrolyte. This allows a direct coupling of photon absorption with electron injection. The model is described in detail, and exemplary numerical results are presented, which demonstrate the feasibility of the model. The influence of the most important material parameters, such as electron mean lifetimes and mobilities, on the cell performance are illustrated.
Complexes of CdSe/ZnS and CdTe quantum dots (QDs) with proteins of reaction centers (RCs) of purple bacteria Rhodobacter sphaeroides have been obtained. An efficient energy transfer from QDs (a donor of electron excitation energy) to RCs (acceptor) is observed for them both in the solution and in the films of crystalline mesoporous titanium oxide. The design of such hybrid structures allows us to increase the absorptive ability of the RC many times and, respectively, increase the efficiency of the light energy conversion into the electrical potential. Such hybrid structures can be used for the development of high-performance solar cells.
Dye-sensitized solar cells (DSCs) using titanium dioxide
(TiO2) electrodes with different haze were investigated. It
was found that the incident photon to current efficiency (\mathit{IPCE})
of DSCs increases with increase in the haze of the TiO2
electrodes, especially in the near infrared wavelength region.
Conversion efficiency of 11.1%, measured by a public test center, was
achieved using high haze TiO2 electrodes. This indicates that
raising the haze of TiO2 electrodes is an effective technique
for improvement of conversion efficiency.
The dye-sensitized solar cells (DSCs) were assembled by using natural carotenoids, crocetin (8,8′-diapocarotenedioic acid) and crocin (crocetin-di-gentiobioside), as sensitizers and their photoelectrochemical properties were investigated taking a presence or absence of carboxylic group in the dye molecule into consideration. In these carotenoids, crocetin that has carboxylic groups in the molecule can attach effectively to the surface of TiO2 film so that it performed the best photosensitized effect resulting in the short-circuit photocurrent with 2.84 mA under irradiation of 1.0 cm2. On the other hand, crocin that has no carboxylic group in the molecule showed lower photoelectrochemical performance because of its lower affinity to the surface of TiO2 film. These results indicate that it is possible to apply carotenoid as sensitizers for DSCs at the presence of effective function groups.