Michael Graetzel

Michael Graetzel
École Polytechnique Fédérale de Lausanne | EPFL · Laboratory of Photonics and Quantum Measurements

About

1,010
Publications
371,506
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202,435
Citations
Citations since 2016
210 Research Items
110364 Citations
201620172018201920202021202205,00010,00015,000
201620172018201920202021202205,00010,00015,000
201620172018201920202021202205,00010,00015,000
201620172018201920202021202205,00010,00015,000

Publications

Publications (1,010)
Article
The tin oxide buffer layer between the transparent conducting oxide current collector and the hematite photoelectrode causes considerable water oxidation enhancement of that electrode. The water oxidation onset potential is lowered by 180 mV. The lifetime of photogenerated charge carriers is increased by a factor of 10. For the investigation of str...
Article
Full-text available
CsPbBr3 has received wide attention due to its superior emission yield and better thermal stability compared to other organic–inorganic lead halide perovskites. In this study, through an interplay of theory and experiments, we investigate the molecular origin of the asymmetric low-temperature photoluminescence spectra of CsPbBr3. We conclude that t...
Article
Its lower bandgap makes formamidinium lead iodide (FAPbI3) a more suitable candidate for single-junction solar cells than pure methylammonium lead iodide (MAPbI3). However, its structural and thermodynamic stability is improved by introducing a significant amount of MA and bromide, both of which increase the bandgap and amplify trade-off between th...
Article
Lead halide perovskites with mixtures of monovalent cations have attracted wide attention due to the possibility of preferentially stabilizing the perovskite phase with respect to photovoltaically less suitable competing phases. Here, we present a theoretical analysis and interpretation of the phase stability of binary (CH6N3)x[HC(NH2)2](1-x)PbI3 =...
Article
Full-text available
5-ammonium valeric acid (AVA) is a frequently used additive in the preparation of lead halide perovskites. However, its microscopic role as passivating, crosslinking or templating agent is far from clear. In this work, we provide density functional theory based structural models for the Ruddlesden-Popper (RP) phases of AVA2(CH3NH3)(n-1)PbnI3n+1 for...
Article
A cobalt-catalyzed cyclotrimerization of bis(aryl)alkyne is used as an innovative tool to obtain hole-transport materials (HTMs). The novel HTM containing six units of oligotriarylamine (HAB1), characterized by UV−vis, cyclic voltammetry, DFT, and thermogravimetric analysis, confirms its suitability as an efficient HTM in PSCs. A PCE of 17.5% was o...
Article
Herein, we describe the synthesis of a hole transporting material based on a partially planarised quart-p-phenylene core incorporating tetraketal and diphenylamine substituents that show optimal energy levels and solubility for perovskite solar cell applications. The triple-cation perovskite devices incorporating such quart-p-phenylene derivatives...
Article
A series of novel polymers (P1−P6) derived from the combination of different units (including thiophene, triarylamine, and spirobifluorene) were successfully synthesized , completely characterized, and used as hole-transporting materials (HTMs) for perovskite solar cells (PSCs). Solar cells with some of these materials as HTMs showed very good perf...
Article
Achieving long-term operational stability at high efficiency level for perovskite solar cells is the most challenging issue toward commercialization of this emerging photovoltaic technology. Here, we investigated the cooperation of Lewis base and Lewis acid by combining the commercial bis-PCBM mixed isomers as Lewis acid in the antisolvent and N-(4...
Article
Full-text available
We report significant improvements in the optoelectronic properties of lead halide perovskites with the addition of monovalent ions with ionic radii close to Pb2+. We investigate the chemical distribution and electronic structure of solution processed CH3NH3PbI3 perovskite structures containing Na+, Cu+ and Ag+, which are lower valence metal ions t...
Article
If opportunely developed and optimized, aqueous dye-sensitized solar cells can be considered a truly low impact photovoltaic device, with no toxic components. Here we report the use of design of experiments as a useful chemometric technique for the concurrent investigation of a series of experimental factors that directly influence the proper opera...
Article
The intrinsic photoluminescence emission properties of high-quality bulk crystals of CH3NH3PbBr3 under excitation by two-photon absorption at 810 nm are presented. A strongly non-monotonous wavelength shift of the two-photon photoluminescence with increasing temperature is observed, which can be associated with discrete transitions between several...
Article
Methylammonium (MA)- and formamidinium (FA)-based organic-inorganic lead halide perovskites provide outstanding performance as photovoltaic materials, due to their versatility of fabrication and their power conversion efficiencies reaching over 22%. The proposition of guanidinium (GUA)-doped perovskite materials generated considerable interest due...
Article
Full-text available
Sequential deposition has been extensively used for the fabrication of perovskite solar cells. Nevertheless, fundamental aspects of the kinetics of methylammonium lead iodide perovskite formation remain obscure. We scrutinize the individual stages of the reaction and investigate the crystallization of the lead iodide film, which occurs before the i...
Article
In the past few years, organic–inorganic metal halide ABX3 perovskites (A = Rb, Cs, methylammonium, formamidinium (FA); B = Pb, Sn; X = Cl, Br, I) have rapidly emerged as promising materials for photovoltaic applications. Tuning the film morphology by various deposition techniques and additives is crucial to achieve solar cells with high performanc...
Article
We report a blue donor-acceptor organic dye, coded as R6, which features a primary chromophore of a polycyclic aromatic hydrocarbon 9,19-dihydrobenzo[1',10']phenanthro[3',4':4,5]thieno[3,2-b]benzo[1,10]phenanthro[3,4-d]thiophene (BPT2) coupled with a diarylamine electron-donor and 4-(7-ethynylbenzo[c][1,2,5]thiadiazol-4-yl)benzoic acid acceptor. Dy...
Article
Full-text available
Perovskite solar cells have achieved power-conversion efficiency values approaching those of established photovoltaic technologies, making the reliable assessment of their operational stability the next essential step towards commercialization. Although studies increasingly often involve a form of stability characterization, they are conducted in n...
Article
A series of [60]fullerenes covalently functionalized with the polyethylene glycol polymer (PEG) is presented. These novel [60]fullerene-based materials have been incorporated as additives in CH3NH3PbI3 (MAPbI3), the most common organic-inorganic perovskite used in perovskite solar cells. The extensive photovoltaic study performed using these materi...
Article
Full-text available
Rapid extraction of photogenerated charge carriers is essential to achieve high efficiencies with perovskite solar cells (PSCs). Here, a new mesoscopic architecture as electron-selective contact for PSCs featuring 40 nm sized TiO2 beads endowed with mesopores of a few nanometer diameters is introduced. The bimodal pore distribution inherent to thes...
Article
We suggest a new degradation mechanism of commonly used gold electrodes in hybrid perovskite solar cells (PSCs) originating from chemical interaction between gold and highly reactive iodine-containing byproducts formed in the course of perovskite decomposition. Intensive UV-irradiation of perovskite would typically lead to the release of volatile I...
Article
Full-text available
The electronic processes occurring within the perovskite solar cells (PSCs) are strongly influenced by the nature of the organic A cations present within the inorganic framework. In this study, the impact of FA (CH(NH2)2⁺) and Cs⁺ cations on the intrinsic and interfacial properties in the FAPbBr3 and CsPbBr3 PSCs is investigated. The analysis of cu...
Article
Full-text available
The effect of Cs-incorporated NiO x on perovskite solar cells with an inverted structure was investigated, where NiO x and PCBM were used as selective contacts for holes and electrons, respectively. It was found that the generation of an Ni phase in an NiO x layer was significantly suppressed by employing cesium. Furthermore, Cs-incorporated NiO...
Article
We designed, synthesized and characterized a novel metal-free organic sensitizer, suitable for the application in dye-sensitized solar cells (DSSCs), both experimentally and theoretically. The structure of the novel donor-acceptor-π-bridge-acceptor (D-A-π-A) dye has triphenylamine (TPA) segment and 4-(Benzo[c][1,2,5] thiadiazol-4-ylethynyl) benzoic...
Conference Paper
Full-text available
We present a new formation strategy of hybrid lead halide perovskites using novel reactants – reactive polyiodide melts (RPM). These compounds, namely, CH3NH3I3+x and HC(NH2)2I3+x, are liquid at room temperature and exhibit extremely high reactivity towards metallic lead and lead compounds (e.g. PbI2, PbO). As a result, perovskite crystals and thin...
Article
Photoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. However, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. In this s...
Article
Full-text available
The achievement of high efficiency and high stability in perovskite solar cells (PSCs) requires optimal selection and evaluation of the various components. After a brief introduction to the perovskite materials and their historical evolution, the first part is devoted to the hole transporting material (HTM), between photoelectrode and dark counter...
Article
Two new donor-acceptor (D-A)-substituted S,N-heteroacene-based molecules were developed and investigated as hole transporting material (HTM) for perovskite solar cells (PSC). Optical and electrochemical characterization brought out that the energy levels of both HTMs are suitable for their use in PSCs. Consequently, an impressive power-conversion e...
Article
Full-text available
Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar-to-hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscop...
Article
The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1% in a few years’ time. At this stage of their development, the key issues concern how to achieve further improvements in efficiency and long-term stability. We review recent developments in the quest to improve the current state of the art. Because photocurr...
Article
Metal halide perovskite absorber materials are about to emerge as a high-efficiency photovoltaic technology. At the same time, they are suitable for high-throughput manufacturing characterized by a low energy input and abundant low-cost materials. However, a further optimization of their efficiency, stability and reliability demands for a more deta...
Article
We demonstrate that by a proper design of a system comprising a perovskite solar cell (PSC) coupled to an electrochemical double-layer capacitor (EDLC), it is possible to simultaneously improve both the PSC and EDLC performance and outperform each single unit behavior. Specifically, we propose a parallel connection of PSC and EDLC of different size...
Article
Photovoltaics (PVs) have been particularly successful in many domestic and industrial settings where opaque PV-covered roofs provide renewable electricity. Modern farming, for an ever growing population, employs vast areas of greenhouses consuming considerable amounts of energy. The majority of greenhouses are not suited to coverage by opaque PVs....
Article
Transporter layers improve stability Although perovskite solar cells can have power conversion efficiencies exceeding 20%, they can have limited thermal and ultraviolet irradiation stability. This is in part because of the materials used to extract the charge carriers (electrons and holes) from the active layer. Arora et al. replaced organic hole t...
Article
Organic semiconductor light absorbers are receiving attention for their potential application in photoelectrochemical (PEC) cells for renewable fuels generation. Key to their advancement is precise control of the interfaces between charge-selective contacts, absorber layers, and electrocatalysts, while maintaining compatibility with an aqueous elec...
Article
The exploration of alternative low-cost molecular hole-transporting materials (HTMs) for both highly efficient and stable perovskite solar cells (PSCs) is a relatively new research area. Two novel HTMs using the thiophene core were designed and synthesized (Z25 and Z26). The perovskite solar cells based on Z26 exhibited a remarkable overall power c...
Article
Hybrid (organic-inorganic) multi-cation lead halide perovskites hold promise for a new generation of easily processable solar cells. Best performing compositions to date are multiple-cation solid alloys of formamidinium (FA), methylammonium (MA), cesium and rubidium lead halides which provide power conversion efficiencies up to around 22%. Here, we...
Article
The influence of interface modification of sensitized TiO2 surfaces by co-adsorbents on photovoltaic performance is detailed. We investigated different functional groups of co-adsorbents, such as carboxylic (4-guanidino butyric acid, chenodeoxycholic acid), phosphinic (dineohexyl phosphinic acid), and phosphonic (dodecyl phosphonic acid), to better...
Article
Full-text available
We found for the first time a new origin of selection of perovskite crystallization pathways from DMF solutions containing MAI and PbI2 to present here a comprehensive study of a full set of essential intermediate phases determining the perovskite’s morphology. For all the three discovered structurally different intermediate phases forming at a giv...
Article
Perovskite solar cells (PSCs) based on cesium (Cs)- and rubidium (Rb)-containing perovskite films show highly reproducible performance; however, a fundamental understanding of these systems is still emerging. Herein, this study has systematically investigated the role of Cs and Rb cations in complete devices by examining the transport and recombina...
Article
Full-text available
Two D-π-A dyes based on fused acenes (carbazole, cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) and dithieno[3,2-b:2',3'-d]pyrrole (DTP)) were synthesized, characterized using UV-vis absorption spectroscopy and electrochemistry, density function theory (DFT) calculations, and used as sensitizers in dye-sensitized solar cells (DSSCs). The two sensitizer...
Article
Full-text available
Among various all-inorganic halide perovskites exhibiting better stability than organic-inorganic halide perovskites, α-CsPbI3 with the most suitable band gap for tandem solar cell application faces an issue of phase instability under ambient conditions. We discovered that a small amount of two-dimensional (2D) EDAPbI4 perovskite containing the eth...
Article
Effective masses are calculated for a large variety of perovskites ABX3 differing in chemical composition (A= Na, Li, Cs; B=Pb, Sn; X= Cl, Br, I) and crystal structure. In addition, the effect of some defects and dopants is assessed. We show that effective masses are highly correlated with the energy of the valence band maximum, conduction band min...
Article
Full-text available
Perovskite solar cells (PSCs) have immense potential for high power conversion efficiency with an ease of fabrication procedure. The fundamental understanding of interfacial kinetics in PSCs is crucial for further improving of their photovoltaic performance. Herein we use the current-voltage (J-V) characteristics and impedance spectroscopy (IS) mea...
Article
Organo-lead halide perovskites have emerged as a promising light harvesting materials for solar cells. The ability to prepare high quality films with a low concentration of defects is essential for obtaining high device performance. Here, we advance the procedure for the fabrication of efficient perovskite solar cells (PSCs) based on mechanochemica...
Article
Perovskite solar cells (PSCs) use perovskites with an APbX3 structure, where A is a monovalent cation and X is a halide such as Cl, Br, and/or I. Currently, the cations for high-efficiency PSCs are Rb, Cs, methylammonium (MA), and/or formamidinium (FA). Molecules larger than FA, such as ethylammonium (EA), guanidinium (GA), and imidazolium (IA), ar...
Article
Novel highly active, optically-transparent electrode catalyst containing Pt, PtOx, graphene oxide and stacked graphene platelet nanofibers is developed for a cathode of Cu(II/I)-mediated dye-sensitized solar cells. The catalyst layer is deposited on a FTO substrate, which thus becomes smoother than the parent FTO, but the button-like Pt/PtOx nanopa...
Article
Full-text available
Nowadays, the efficient, stable, and scalable conversion of solar energy into chemical fuels represents a great scientific, economic, and ethical challenge. Amongst the available candidate technologies, photoelectrochemical water-splitting potentially has the most promising technoeconomic trade-off between cost and efficiency. However, research on...
Article
The kinetics of photoelectrochemical (PEC) oxidation of methanol, as a model organic substrate, on α-Fe2O3 photoanodes are studied using photo-induced absorption spectroscopy and transient photocurrent measurements. Methanol is oxidized on α-Fe2O3 to formaldehyde with near unity Faradaic efficiency. A rate law analysis under quasi-steady state cond...
Article
Perovskite solar cells (PSC) have emerged as a potential candidate for high efficiency low-cost photovoltaic technology. However, intrinsic and interfacial responses of PSC under photo and bias-induced degradation and recovery have not been clearly understood. Herein, the influence of illumination and bias on intrinsic and interfacial characteristi...
Article
Full-text available
Here we introduce a new solvent-free preparation method for hybrid metal halide perovskites involving the direct reaction of metallic lead with polyiodide melts. We discovered new reactive polyiodide melts (RPMs) that can be prepared simply by adding elemental iodine to halide salts of the organic A cations of the common hybrid perovskites, e.g. me...
Article
Full-text available
Solid-state dye-sensitized solar cells currently suffer from issues such as inadequate nanopore filling, low conductivity and crystallization of hole-transport materials infiltrated in the mesoscopic TiO2 scaffolds, leading to low performances. Here we report a record 11% stable solid-state dye-sensitized solar cell under standard air mass 1.5 glob...
Data
Supplementary Figures, Supplementary Table and Supplementary References
Article
The surge of the power conversion efficiency of metal halide lead perovskite solar cells comes with concerns, such as the long-term ecotoxicity of lead compounds, their sensitivity toward moisture and oxygen, or the scarcity of some of their components. Most perovskite solar cells still suffer from serious stability problems when measured under rea...
Article
Full-text available
The solar-driven electrochemical reduction of CO2 to fuels and chemicals provides a promising way for closing the anthropogenic carbon cycle. However, the lack of selective and Earth-abundant catalysts able to achieve the desired transformation reactions in an aqueous matrix presents a substantial impediment as of today. Here we introduce atomic la...
Article
Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are sti...