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Abstract

Organic photovoltaics (OPVs) possess the advantageous trait of solution processability, which is often included in the rationale for pursuing new insight into OPV materials; however, OPV blends typically use hazardous chlorinated solvents for processing. In order to realize the full advantages of OPVs, as well as growing to an industrial scale, the use of environmentally friendly solvents for processing OPVs needs to be pursued. In this study, we utilized the well-studied polymer PBnDT-FTAZ system as the model conjugated polymer, and synthesized a series of structurally similar conjugated polymers with oligo(ethylene glycol) side-chains, aiming to understand the structural requirements to convert conventional conjugated polymers into green-processable alternatives. We elucidated the impact of these OEG chains on the properties of modified original polymer, including solubility and optoelectronic properties. Finally, aiming to understand the impact of changing side chains to the device performance, we fabricated solar cells with a non-fullerene acceptor (IT-M), achieving decent device efficiencies (7%). Additionally, using renewable and green solvent, 2-MeTHF, we were able to achieve device efficiencies of 2%.

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... The most significant green-solvent processable OPV studies involving the molecular engineering strategy and performed in the last 4 years are reviewed here. This strategy has been used to make organic semiconductors soluble and processable in a variety of green solvents such as toluene [30][31][32][33][34]74,75], ethylbenzene [35], o-xylene [36][37][38][39]76,77], p-xylene [40], 1,2,4-trimethylbenzene (1,2,4-TMB) [41], tetrahydrofuran [42][43][44][45]78,79] (THF), 2-methyl-THF [46][47][48], anisole [49], 2-methylanisole (2-MA) [50], and water/ethanol mixtures [51,52]. This strategy has been applied to both donors [30,31,34,36,37,42,43,46,47,50,76,78] and acceptors [32,33,[38][39][40][41]45,48,49,51,74,75,77,79]. ...
... This strategy has been used to make organic semiconductors soluble and processable in a variety of green solvents such as toluene [30][31][32][33][34]74,75], ethylbenzene [35], o-xylene [36][37][38][39]76,77], p-xylene [40], 1,2,4-trimethylbenzene (1,2,4-TMB) [41], tetrahydrofuran [42][43][44][45]78,79] (THF), 2-methyl-THF [46][47][48], anisole [49], 2-methylanisole (2-MA) [50], and water/ethanol mixtures [51,52]. This strategy has been applied to both donors [30,31,34,36,37,42,43,46,47,50,76,78] and acceptors [32,33,[38][39][40][41]45,48,49,51,74,75,77,79]. ...
... Small OPV cells based on the PAL PM7:IT-4F and processed from toluene achieved an impressive PCE of 13.1%, much higher than the PCE of 5.8% exhibited by similar PBDB-T:IT-4F devices also processed from toluene. Chen et al. [31] considered the conjugated polymer PBnDT-FTAZ (briefly FTAZ), first synthesized in 2011 [80], as model system and systematically replaced its branched alkyl chains with oligo(ethylene glycol) (OEG) side-chains. Some of the novel synthesized polymers donors exhibited good solubility in toluene (P2, P3, and P6) and these were tested, with the acceptor IT-M, in toluene-processed devices achieving a highest PCE of 7.1% with the system P2:IT-M. ...
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Over the last four years, tremendous progress has occurred in the field of organic photovoltaics (OPVs) and the champion power conversion efficiency (PCE) under AM1.5G conditions,as certified by the National Renewable Energy Laboratory (NREL), is currently 18.2%. However,these champion state-of-the-art devices were fabricated at lab-scale using highly toxic halogenated solvents which are harmful to human health and to the environment. The transition of OPVs from the lab to large-scale production and commercialization requires the transition from halogenatedsolvent-processing to green-solvent-processing without compromising the device’s performance. This review focuses on the most recent research efforts, performed since the year 2018 onwards, in the development of green-solvent-processable OPVs and discusses the three main strategies that are being pursued to achieve the proposed goal, namely, (i) molecular engineering of novel donors and acceptors, (ii) solvent selection, and (iii) nanoparticle ink technology.
... In recent years, based on the desire for green solvent processing [24][25][26], the OSC field has begun to pay attention to green solvent processable OSC materials with OEG side chains [23,27,28]. The OEG side chain engineering has been regarded as a productive way ahead to improve the performance of OSC materials [29]. Most OEG modified materials are designed and synthesized based on classical conjugated backbone structures. ...
... In 2019, a series of water/ethanol-soluble naphthalenediimide (NDI)-based polymer acceptors P(NDIDEG-T), P(NDITEG-T), and P(NDITEG-T2) were also reported by Woo et al.; the efficient aqueous-processed all-polymer solar cell was achieved with a maximum PCE of 2.15% [30]. Meanwhile, a series of OCS polymer PBnDTs (PBnDT-FTAZ NO , PBnDT-OTAZ, PBoDT-FTAZ, PBoDT-FTAZ NO , and PBoDT-OTAZ) modified with OEG side chains were successively synthesized by our group in 2019 [29]. The effects of OEG side chains on the solubility, optoelectronic and photovoltaic properties of modified PBnDT-FTAZ were systematically investigated [31]. ...
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Introduced oligo(ethylene glycol) (OEG) chains into high-performance donor-acceptor (D-A) type conjugated polymers is a promising strategy to control the π-π stacking, energy levels, solubility, and electrical properties. In this work, a series of novel PDTBF polymers (PDTBF-DTh, PDTBF-ThSe, and PDTBF-Th) were synthesized based on the typical benzothiadiazole-thiophene (BT-Th)-based polymer substituted with OEG side chains to investigate their electrochromic (EC) and photovoltaic performance. The resultant PDTBF polymers had fast switching speed (i.e., chlorobenzene-prepared PDTBF-Th EC film: T0.9 c = 1.8 s, T0.9 b = 1.0 s), and high coloration efficiencies (i.e., chlorobenzene-prepared PDTBF-ThSe EC film: 255.50 cm² C⁻¹). Moreover, the PDTBF-DTh:Y6-based device shows a power conversion efficiency (PCE) of 3.11%. Due to the induced amphiphilic OEG side chains on the backbone of the conjugated polymer, these materials also exhibited green solvent processing potential. It is worth noting that these PDTBF polymers exhibited much wider optical bandgaps (1.95 eV–2.16 eV) than other reported PDTBF polymers (mostly narrow band gaps: 1.40–1.70 eV), due to the format of linkage between OEG side chains and thiophene units. It is an effective strategy to control the optical properties of the conjugated polymers using OEG side chain engineering investigation.
... In addition, carbazole derivatives have fully aromatic properties and they are able to form stable radical cations. They also have relatively high charge carrier mobilities and they show good photochemical and thermal stabilities [16].The nitrogen atom in the carbazole unit is easily functionalized with different alkyl chains for enhancing solubility of the resulting polymers [17,18]. ...
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In this work four novel donor-acceptor copolymers, PCDTBTDI-DMO, PCDTBTDI-8, P2F-CDTBTDI-DMO and P2F-CDTBTDI-8, were designed and synthesised via Suzuki polymerisation. The first two copolymers consist of 2,7-carbazole flanked by thienyl moieties as the electron donor unit and benzothiadiazole dicarboxylic imide (BTDI) as electron acceptor units. In the structures of P2F-CDTBTDI-DMO and P2F-CDTBTDI-8 copolymers, two fluorine atoms were incorporated at 3,6-positions of 2,7-carbazole to investigate the impact of fluorine upon the optoelectronic, structural and thermal properties of the resulting polymers. P2F-CDTBTDI-8 possesses the highest number average molecular weight (M n = 24,200 g mol −1) among all the polymers synthesised. PCDTBTDI-DMO and PCDTBTDI-8 show identical optical band gaps of 1.76 eV. However, the optical band gaps of fluorinated copolymers are slightly higher than non-fluorinated counterparts. All polymers have deep-lying highest occupied molecular orbital (HOMO) levels. Changing the alkyl chain substituents on BTDI moieties from linear n-octyl to branched 3,7-dimethyloctyl groups as well as substituting the two hydrogen atoms at 3,6-positions of carbazole unit by fluorine atoms has negligible impact on the HOMO levels of the polymers. Similarly, the lowest unoccupied molecular orbital (LUMO) energy levels are almost comparable for all polymers. Thermogravimetric analysis (TGA) has shown that all polymers have good thermal stability and also confirmed that the fluorinated copolymers have higher thermal stability relative to those non-fluorinated analogues. Powder X-ray diffraction (XRD) studies proved that all polymers have an amorphous nature in the solid state.
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Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large Voc of 1.01 V and a Jsc of 17.89 mA cm−2. Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs. A series of wide bandgap donor polymers are designed and synthesized by incorporating a monothiophene functionalized with both a fluorine atom and an ester group. Fabricated from nonhalogenated solvent, power conversion efficiencies of 11.39% and 12.11% are achieved for binary and ternary nonfullerene solar cells, respectively.
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The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within the past five years, there have been over 100 nonfullerene acceptor molecules synthesized, and the power conversion efficiency of nonfullerene organic solar cells has increased dramatically, from ∼2% in 2012 to >13% in 2017. This review summarizes this progress, aiming to describe the molecular design strategy, to provide insight into the structure–property relationship, and to highlight the challenges the field is facing, with emphasis placed on most recent nonfullerene acceptors that demonstrated top-of-the-line photovoltaic performances. We also provide perspectives from a device point of view, wherein topics including ternary blend device, multijunction device, device stability, active layer morphology, and device physics are discussed.
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Over the past three years, a particularly exciting and active area of research within the field of organic photovoltaics has been the use of non-fullerene acceptors (NFAs). Compared with fullerene acceptors, NFAs possess significant advantages including tunability of bandgaps, energy levels, planarity and crystallinity. To date, NFA solar cells have not only achieved impressive power conversion efficiencies of ~13–14%, but have also shown excellent stability compared with traditional fullerene acceptor solar cells. This Review highlights recent progress on single-junction and tandem NFA solar cells and research directions to achieve even higher efficiencies of 15–20% using NFA-based organic photovoltaics are also proposed. This Review describes how non-fullerene electron acceptor materials are bringing improvements in the power conversion efficiency and stability of organic solar cells.
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Non-fullerene acceptors (NFAs) are currently a major focus of research in the development of bulk-heterojunction organic solar cells (OSCs). In contrast to the widely used fullerene acceptors (FAs), the optical properties and electronic energy levels of NFAs can be readily tuned. NFA-based OSCs can also achieve greater thermal stability and photochemical stability, as well as longer device lifetimes, than their FA-based counterparts. Historically, the performance of NFA OSCs has lagged behind that of fullerene devices. However, recent developments have led to a rapid increase in power conversion efficiencies for NFA OSCs, with values now exceeding 13%, demonstrating the viability of using NFAs to replace FAs in next-generation high-performance OSCs. This Review discusses the important work that has led to this remarkable progress, focusing on the two most promising NFA classes to date: rylene diimide-based materials and materials based on fused aromatic cores with strong electron-accepting end groups. The key structure–property relationships, donor–acceptor matching criteria and aspects of device physics are discussed. Finally, we consider the remaining challenges and promising future directions for the NFA OSCs field.
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The power conversion efficiencies (PCEs) of state-of-the-art organic solar cells (OSCs) have increased to over 13%. However, the most commonly used solvents for making the solutions of photoactive materials and the coating methods used in laboratories are not adaptable for future practical production. Therefore, taking a solution-coating method with environmentally friendly processing solvents into consideration is critical for the practical utilization of OSC technology. In this study, a highly efficient PBTA-TF:IT-M-based device processed with environmentally friendly solvents, tetrahydrofuran/isopropyl alcohol (THF/IPA) and o-xylene/1-phenylnaphthalene, is fabricated; a high PCE of 13.1% can be achieved by adopting the spin-coating method, which is the top result for OSCs. More importantly, a blade-coated non-fullerene OSC processed with THF/IPA is demonstrated for the first time to obtain a promising PCE of 11.7%; even for the THF/IPA-processed large-area device (1.0 cm²) made by blade-coating, a PCE of 10.6% can still be maintained. These results are critical for the large-scale production of highly efficient OSCs in future studies.
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The majority of organic semiconductors have a low relative dielectric constant (εr < 6), which is an important limitation for organic solar cells (OSCs). A high dielectric constant would reduce the exciton binding energy, reduce charge carrier recombination losses, and thereby enhance the overall device performance of OSCs. However, the development of organic/polymeric semiconductors with higher dielectric constant (εr > 6) attracted very limited attention. Moreover, the high performance OSCs based on high dielectric constant photovoltaic materials is still in its infancy. Herein, we report an oligoethylene oxide side chain-containing non-fullerene acceptor (ITIC-OE) with a high relative dielectric constant of εr ≈ 9.4, which is two times larger than its alkyl chain-containing counterpart ITIC. Encouragingly, the OSCs based on ITIC-OE show high power conversion efficiency of 8.5%, which is the highest value for OSCs that employ high dielectric constant materials. Nevertheless, this value is lower than that of ITIC-based control devices. The less phase-separated morphology in blend films due to the reduced crystallinity of ITIC-OE and the too good miscibility between PBDB-T and ITIC-OE are responsible for the lower device performance. This work suggests additional prerequisites to make high dielectric constant playing a significant role in OSCs.
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Though the power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been boosted to 12%, the use of highly pollutive halogenated solvents as the processing solvent significantly hinders the mass production of OSCs. It is thus necessary to achieve high-efficiency OSCs by utilizing the halogen-free and environmentally-friendly solvents. Herein, we applied a halogen-free solvent system (o-xylene/1-phenylnaphthalene, XY/PN) for fabricating fullerene-free OSCs, and a high PCE of 11.6% with a notable fill factor (FF) of 72% was achieved based on the PBDB-T:IT-M blend, which is among the top efficiencies of halogen-free solvent processed OSCs. In addition, the influence of different halogen-free solvent additives on the blend morphology and device performance metrics was studied by synchrotron-based tools and other complementary methods. Morphological results indicate the highly ordered molecular packing and highest average domain purity obtained in the blend films prepared by using XY/PN co-solvent are favorable for achieving increased FFs and thus higher PCEs in the devices. Moreover, a lower interaction parameter (χ) of the IT-M:PN pair provides a good explanation of the more favorable morphology and performance in devices with PN as the solvent additive, relative to those with DPE ad NMP. Our study demonstrates that carefully screening the non-halogenated solvent additive plays a vital role in realizing the efficient and environmentally-friendly solvent processed OSCs.
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Significant efforts have lead to demonstrations of nonfullerene solar cells (NFSCs) with record power conversion efficiency up to ≈13% for polymer:small molecule blends and ≈9% for all-polymer blends. However, the control of morphology in NFSCs based on polymer blends is very challenging and a key obstacle to pushing this technology to eventual commercialization. The relations between phases at various length scales and photovoltaic parameters of all-polymer bulk-heterojunctions remain poorly understood and seldom explored. Here, precise control over a multilength scale morphology and photovoltaic performance are demonstrated by simply altering the concentration of a green solvent additive used in blade-coated films. Resonant soft X-ray scattering is used to elucidate the multiphasic morphology of these printed all-polymeric films and complements with the use of grazing incidence wide-angle X-ray scattering and in situ spectroscopic ellipsometry characterizations to correlate the morphology parameters at different length scales to the device performance metrics. Benefiting from the highest relative volume fraction of small domains, additive-free solar cells show the best device performance, strengthening the advantage of single benign solvent approach. This study also highlights the importance of high volume fraction of smallest domains in printed NFSCs and organic solar cells in general.
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Solution-processable organic photovoltaics (OPV) has emerged as a promising clean energy-generating technology due to its potential for low-cost manufacturing with a high power/weight ratio. The state-of-the-art OPV devices are processed by hazardous halogenated solvents. Fabricating high-efficiency OPV devices using greener solvents is a necessary step toward their eventual commercialization. In this review, recent research efforts and advances in green-solvent-processable OPVs are summarized, and two basic strategies including material design and solvent selection of light-harvesting layers are discussed. In particular, the most recent green-solvent-processable OPVs with high efficiencies in excess of 9% are highlighted.
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The most efficient plastic solar cells comprise a blend of conjugated polymer and a suitable electron acceptor, typically a fullerene derivative. Therefore narrow-bandgap conjugated polymers are currently sought for the fabrication of such devices. A significant challenge is being able to predict device function and performance from consideration of the molecular connectivity and dimensions of the partners within the active layer. Improved chemical syntheses are therefore required to make structurally varied polymers and enable the delineation of structure-function relationships with the aim of improving power conversion efficiencies. Here, we demonstrate that microwave heating in combination with the screening of comonomer reactant ratios can be used to obtain donor-acceptor copolymers with high average molecular weights and properties that make them suitable for solar cell incorporation. Furthermore, we highlight the importance of high molecular weight and the contribution of solubilizing side groups in determining the final device properties.
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In this work, a medium bandgap quinoxaline (Qx) based polymer, named TTFQx‐T1, and a narrow bandgap n‐type polymer, named N2200, are employed to fabricate all‐polymer solar cells (all‐PSCs), which exhibited good light absorption for high short circuit current density (Jsc), well‐matched molecular energy level for good charge separation and high open circuit voltage (Voc). Chlorinated solvents are harmful to both the environment and human beings; therefore, it is important to develop environmentally friendly solvents. Considering this, the green solvent tetrahydrofuran (THF) was employed to process all‐PSCs. The blend films based on TTFQx‐T1:N2200 processed with THF and thermal annealing (TA) exhibited better phase separation and preferential face‐on orientation toward the substrate, which benefited the exciton dissociation and charge carrier mobilities for higher FF and Jsc. The optimized device based on TTFQx‐T1:N2200 delivered an efficient power conversion efficiency of 8.63%, which is the highest value for all‐PSCs from Qx based polymers. Additive‐free all‐polymer solar cells (all‐PSCs) devices based on TTFQx‐T1:N2200 are fabricated and the active layer (TTFQx‐T1:N2200) processed with THF and CHCl3. The optimized device processed with THF exhibited better photovoltaic properties than that processed with CHCl3. This work afforded a feasible strategy for constructing high‐performance all‐PSCs via a simple eco‐friendly processing method.
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Non-fullerene acceptors based organic photovoltaics (OPVs) have attracted considerable attention in the last decade due to their great potential to realize high-power conversion efficiencies. To achieve higher performance OPVs, the fundamental challenges are in enabling efficient charge separation/transport and a low voltage loss at the same time. Here, we have designed and synthesized a new class of non-fullerene acceptor, Y6, that employs an electron-deficient-core-based central fused ring with a benzothiadiazole core, to match with commercially available polymer PM6. By this strategy, the Y6-based solar cell delivers a high-power conversion efficiency of 15.7% with both conventional and inverted architecture. By this research, we provide new insights into employing the electron-deficient-core-based central fused ring when designing new non-fullerene acceptors to realize improved photovoltaic performance in OPVs.
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In this work, we developed two novel low bandgap copolymers by ethylenedioxythiophene (EDOT) side chain engineering, PTB-EDOT and PTB-EDOTS, for fabricating green solvent-processed but highly efficient non-fullerene organic solar cells (NF-PSCs). This molecular design strategy not only featured the copolymers with excellent solubility in green solvent of 2-methyltetrafuran (MeTHF), but also introduced low-lying HOMO level, high extinction coefficient and good crystallinity. PTB-EDOTS-based binary blend NF-PSCs showed a PCE of 9.28% when using ITIC-Th as acceptor and chlorobenzene/1-chloronaphthalene (CB/CN) as processing solvent. If using MeTHF instead of CB/CN, the PCE was further improved to 10.18%. To make up the weak absorption in short wavelength region and further optimize the morphology, a large bandgap polymer donor (J71) was added as the third component to fabricate ternary blend NF-PSCs. After adding 20 wt% of J71, NF-PSCs exhibited improved absorption and fine-tuned morphology. The charge and energy transfer were also promoted by such ternary blend strategy through electron cascade structure, hole back phenomenon and Förster resonance energy transfer (FRET) process, boosting the top PCE of 12.26% with a very high fill factor (FF) of 75.6%. To our best knowledge, this is the best record for NF-PSCs using green solvents.
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The authors report the development of a desirable aqueous process for ecofriendly fabrication of efficient and stable organic field‐effect transistors (eco‐OFETs) and polymer solar cells (eco‐PSCs). Intriguingly, the addition of a typical antisolvent, water, to ethanol is found to remarkably enhance the solubility of oligoethylene glycol (OEG) side chain‐based electroactive materials (e.g., the highly crystalline conjugated polymer PPDT2FBT‐A and the fullerene monoadduct PC61BO12). A water–ethanol cosolvent with a 1:1 molar ratio provides an increased solubility of PPDT2FBT‐A from 2.3 to 42.9 mg mL⁻¹ and that of PC61BO12 from 0.3 to 40.5 mg mL⁻¹. Owing to the improved processability, efficient eco‐OFETs with a hole mobility of 2.0 × 10⁻² cm² V⁻¹ s⁻¹ and eco‐PSCs with a power conversion efficiency of 2.05% are successfully fabricated. In addition, the eco‐PSCs fabricated with water–ethanol processing are highly stable under ambient conditions, showing the great potential of this new process for industrial scale application. To better understand the underlying role of water addition, the influence of water addition on the thin‐film morphologies and the performance of the eco‐OFETs and eco‐PSCs are studied. Additionally, it is demonstrated that the application of the aqueous process can be extended to a variety of other OEG‐based material systems.
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Though organic photovoltaic cells (OPVs) have many advantages, their performance still lags far behind that of other photovoltaic platforms. One of the most fundamental reasons for this is the low charge mobility of organic materials, leading to a limit on the active layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic materials, a record and certified 17.29% power conversion efficiency for a 2-terminal monolithic solution processed tandem OPV is achieved.
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We present a new series of fullerene derivatives that exhibit solubility in ethanol/water solvent mixtures and implement these materials to fabricate polymer solar cells (PSCs) using environmentally benign solvents. In order to simultaneously optimize the processability of the fullerenes in ethanol/water solvent mixtures and device performance, different fullerene mono-adducts were designed by introducing oligoethylene glycol (OEG) side chains with different lengths and number of branches. As a result, we achieved power conversion efficiencies (PCE) up to 1.4% for PSCs processed from benign ethanol/water mixtures in air. Significantly, the new alcohol/water-soluble fullerene derivatives displayed electron mobilities up to 1.30 × 10-4 cm2 V-1 s-1, 150 times higher than those of a previously reported alcohol-soluble fullerene bisadduct, owing to efficient packing of the fullerenes. Femtosecond transient absorption spectroscopy revealed the acceptor side chain to markedly impact geminate and/or nongeminate charge recombination in the PSCs. In addition, side-chain optimization of these fullerenes produced well-intermixed morphologies with high domain purity when blended with p-type polymer to provide hole and electron transport pathways. Our results provide important guidelines for the design of electroactive materials for safe and environmentally benign fabrication of PSCs and other organic electronic devices.
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Through ease of scalability and facile synthetic methods, eight N‐annulated perylene diimide dimers with different aliphatic chains are synthesized and evaluated as non‐fullerene acceptors in organic solar cells (OSCs). Optical absorption and emission spectroscopy, and cyclic voltammetry are used to characterize the materials. Variation of the length and topology of the aliphatic chains attached at the pyrrolic N‐position is shown to have minimal effect on properties in solution. As films, the use of a branched aliphatic chains results in the dimer exhibiting a low energy shoulder in the absorption spectrum and a narrower emission band. OSCs are fabricated and tested in air, at room temperature, using an inverted architecture. The polymer PTB7‐Th is used as the donor and all active layers are processed from 2‐methyltetrahydrofuran. OSC power conversion efficiencies are shown to vary from 3.7%–5.4% for OSCs. The dimer with 2‐ethylhexyl aliphatic chains is selected for optimization because of a high organic solvent solubility and excellent film formation properties. Use of the solvent additive 1,8‐diiodooctane during film formation lead to an increase in efficiency to 6.6%, while halogen‐free processed OSCs reach 6%. This result offers a simple method for materials side‐chain engineering for the development of OSCs processed in air from eco friendly solvents. The “side‐chain” engineering of N‐annulated perylene diimide (PDI) molecular dimeric materials is presented. Changing the length and topology of the alkyl side chain affects both materials solubility and self‐assembly. Polymer solar cells using the new PDI materials as electron acceptors can be processed from green solvents, in air, at room temperature and exhibit good, reproducible performance.
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So far, the most successful and widely used solvents in polymer solar cells (PSCs) are chlorinated solvents like chloroform (CF), 1,2-dichlorobenzene (DCB) and chlorobenzene (CB), which are highly detrimental to human health and the environment. In this work, by the approach of manipulating flexible and conjugated side groups of a widely used polymer donor material (PBDB-T), two new polymers named PBDB-T-BO and PBDB-BzT are designed and synthesized to improve the solubility and fine-tune the aggregation property in tetrahydrofuran (THF), a much more benign solvent. As a result, an outstanding PCE of 12.10% was achieved with THF-processed PBDB-BzT:IT-M device. The result in this work demonstrates the importance to modulate the aggregation effect of the polymer in solution by inserting conjugated groups and also suggests a feasible method to convert the main processing solvent of a highly efficient non-fullerene (NF)-PSCs from CB into THF.
Article
Conjugated polymers applied in organic electronics (notably photovoltaics and photodetectors) generally exhibit relatively low dielectric constants (εr 3−4), which leads to significant recombination losses of photogenerated excitons. As a direct consequence, the performance of the resulting devices is inherently restricted. Some efforts have been directed toward increasing εr of the photoactive organic compounds, but the general knowledge on the impact of specific structural variations on the dielectric constant and the final device output remains rather limited. In this study, this problem is addressed. A series of push-pull type alternating copolymers is synthesized based on 4H-cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) and 4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD) subunits, with the aim to increase the dielectric constant using oligo(ethylene glycol) side chains. The amount of glycol substituents on the polymer backbone is gradually raised to systematically investigate its influence on the dielectric properties. Impedance measurements reveal a doubling of the dielectric constant (up to εr 6.3) with respect to the reference polymer. Upon applying these materials in bulk heterojunction polymer solar cells, an efficiency of 4.4% is obtained for the best-performing device, with a particularly higher short-circuit current and improved fill factor compared to the pristine alkyl-substituted polymer. Importantly, a non-halogenated solvent – beneficial toward ‘green’ processing – can also be applied for the active layer deposition, affording comparable results.
Article
Organic photovoltaics (OPV) offer a low-cost and esthetically appealing thin-film alternative to the well-known silicon-based solar panels, opening up new applications and markets. A substantial increase in power conversion efficiency (to over 13%) has been achieved for these organic solar cells over the last decade, largely as a result of intensive research on novel electron donor and acceptor materials, combined in a bulk heterojunction device structure. Nevertheless, it is clear that further progress is required to be competitive with more efficient traditional and other emerging thin-film PV technologies. At this moment, the device performance is (among others) limited by the low dielectric constants (εr = ~3-4) of the state of the art photoactive organic materials. Important loss processes inherently connected to the strong Coulombic interactions within low-permittivity organic materials can be suppressed through the enhancement of εr. High dielectric constant materials show lower exciton binding energies and hence recombination can be reduced, improving the charge carrier extraction efficiency. Despite these promising prospects, limited research has been devoted to the development and OPV integration of high-dielectric organic semiconductors. In here, an overview is provided of the approaches applied so far to enhance εr of organic compounds specifically developed for OPV purposes, commenting on the insights obtained and the challenges remaining.
Article
Organic–inorganic hybrid perovskite has led to the development of new solar cells with outstanding efficiency. In perovskite solar cells (PSCs), perovskite is sandwiched between a working electrode (fluorine-doped tin oxide) and a counter electrode (gold, Au). In order to transport charges and block opposite charges, charge transport layers are inserted between perovskite and the electrodes. In particular, a hole transport layer is important because it generally prevents perovskite from exposure to air. Therefore, it is necessary to investigate dopant-free and hydrophobic polymeric hole transport materials (HTMs). In this study, a novel polymeric HTM (PTEG) is synthesized by controlling the solubility using a tetraethylene glycol group. The planar-PSC employing PTEG exhibits an efficiency of 19.8% without any dopants, which corresponds to the highest value reported to date. This study offers a fundamental strategy for designing and synthesizing various polymeric HTMs.
Article
Organic solar cells (OSCs) have been a rising star in the field of renewable energy since the introduction of the bulk heterojunction (BHJ) in 1992. Recent advances have pushed the efficiencies of OSCs to over 13%, an impressive accomplishment via collaborative efforts in rational materials design and synthesis, careful device engineering, and fundamental understanding of device physics. Throughout these endeavors, several design principles for the conjugated donor polymers used in such solar cells have emerged, including optimizing the conjugated backbone with judicious selection of building blocks, side-chain engineering, and substituents. Among all of the substituents, fluorine is probably the most popular one; improved device characteristics with fluorination have frequently been reported for a wide range of conjugated polymers, in particular, donor–acceptor (D–A)-type polymers. Herein we examine the effect of fluorination on the device performance of solar cells as a function of the position of fluorination (on the acceptor unit or on the donor unit), aiming to outline a clear understanding of the benefits of this curious substituent.
Article
For solution processability of polymer solar cells (PSCs), polymer electron donors are almost always composed of conjugated main chain and flexible alkyl side chains. In this paper, we report a polymer electron donor based on isoindigo unit bearing branched oligo(ethylene glycol) (OEG) side chains, P-OEG. Compared with the control polymer bearing alkyl side chains (P-Alkyl), P-OEG exhibits not only smaller π-π stacking distance and redshifted absorption spectra, but also larger surface energy for better compatibility with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) electron acceptor. PSC device of P-OEG exhibits the open-circuit voltage (VOC) of 0.73 V, short-circuit current density (JSC) of 13.92 mA cm-2, fill factor (FF) of 0.50, corresponding to the power conversion efficiency (PCE) of 5.10%. This performance is higher than that of P-Alkyl (PCE = 3.0%), which is attributed to the finer phase separation morphology of P-OEG:PC71BM blend than that of P-Alkyl:PC71BM blend. These results suggest that branched OEG side chain is an effective approach to improve PSC device performance of some polymer electron donors.
Article
A wide-bandgap polymer, (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(2,5-(methyl thiophene carboxylate))]) (3MT-Th), is synthesized to obtain a complementary broad range absorption when harmonized with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC). The synthesized regiorandom 3MT-Th polymer shows good solubility in nonhalogenated solvents. A film of 3MT-Th:ITIC can be employed for forming an active layer in a polymer solar cell (PSC), with the blend solution containing toluene with 0.25% diphenylether as a nonhalogenated additive. The corresponding PSC devices display a power conversion efficiency of 9.73%. Moreover, the 3MT-Th-based PSCs exhibit excellent shelf-life time of over 1000 h and are operationally stable under continuous light illumination. Therefore, methyl thiophene-3-carboxylate in 3MT-Th is a promising new accepting unit for constructing p-type polymers used for high-performance nonfullerene-type PSCs.
Article
hrough introducing six fluorine atoms onto quinoxaline (Qx), a new electron acceptor unit-hexafluoroquinoxaline (HFQx) is firstly synthesized. Based on this unit, we synthesize a new donor-acceptor (D-A) copolymer (HFQx-T), which is composed of benzodithiophene (BDT) derivative donor block and an HFQx accepting block. The strong electron-withdrawing properties of fluorine atoms increase significantly the voltage open-circuit (Voc) by tuning the highest occupied molecular orbital (HOMO) energy level. In addition, fluorine atoms enhance the absorption coefficient of the conjugated copolymer and change the film morphology, which implies an increase of the short-circuit current density (Jsc) and fill factor (FF). Indeed, the HFQx-T:ITIC blended film achieves an impressive power conversion efficiency (PCE) of 9.4% with large short-current density (Jsc) of 15.60 mA/cm2, high Voc of 0.92 V and FF of 65% via two step annealing (thermal annealing (TA) and solvent vapor annealing (SVA) treatments). The excellent results obtained, show that the new copolymer HFQx-T synthesized could be a promising candidate for organic photovoltaics.
Article
We report eco- and human-friendly fabrication of organic field-effect transistors (OFETs) and polymer solar cells (PSCs) using only ethanol as a processing solvent at ambient condition, in stark contrast to that involving the use of halogenated and/or aromatic solvents. New ethanol-processable electroactive materials, p-type polymer (PPDT2FBT-A) and n-type bis-adduct fullerene acceptor (Bis-C60-A) are designed rationally by incorporation of oligoethylene glycol (OEG) side-chains. By ethanol processing, PPDT2FBT-A shows a broad light absorption in the range of 300–700 nm and highly crystalline interchain ordering with out-of-plane interlamellar scattering up to (400) with strong π–π stacking. As a result, the ethanol-processed PPDT2FBT-A OFETs yield high charge-carrier mobilities up to 1.0 × 10–2 cm² V–1 s–1, which is the highest value reported to date from alcohol-processed devices. Importantly, the ethanol-processed PPDT2FBT-A OFET outperformed that processed using typical processing solvent, chlorobenzene (CB), with ∼10-fold enhancement in hole mobility, because the highly edge-on oriented packing of PPDT2FBT-A was produced by ethanol-process. Also, for the first time, significant photovoltaic performance was achieved for the ethanol-processed device of PPDT2FBT-A and Bis-C60-A due to the formation of an interpenetrating nanofibrillar morphology of highly crystalline PPDT2FBT-A polymers. The relationships between molecular structure, nanoscale morphology and electronic properties within ethanol-processed OFETs and PSCs were elucidated by comparing to typical CB-processed devices. These comparisons provide important guidelines for the design of new ethanol/water-soluble active layer materials and their use in the development of green solvent-processed efficient OFETs and PSCs.
Article
Solution-processed organic films are a facile route to high-speed, low cost, large-area deposition of electrically functional components (transistors, solar cells, emitters, etc.) that can enable a diversity of emerging technologies, from Industry 4.0, to the Internet of things, to point-of-use heath care and elder care. The extreme sensitivity of the functional performance of organic films to structure and the general nonequilibrium nature of solution drying result in extreme processing–performance correlations. In this Review, we highlight insights into the fundamentals of solution-based film deposition afforded by recent state-of-the-art in situ measurements of functional film drying. Emphasis is placed on multimodal studies that combine surface-sensitive X-ray scattering (GIWAXS or GISAXS) with optical characterization to clearly define the evolution of solute structure (aggregation, crystallinity, and morphology) with film thickness.
Article
Increasing interests have been devoted to developing high-performance all polymer solar cells (all-PSCs) owing to their specific advantages in light absorption and long-term stability. In this work, we systematically investigated the synergistic effects of processing solvents and molecular weight on the photovoltaic performance of all-PSCs, which consist of an n-type of polymer N2200, and a p-type of wide bandgap polymer PTzBI that are made up of benzodithiophene and imide functionalized benzotriazole unit. It is noted that increasing the molecular weight of N2200 can simultaneously enhance the exciton generation and dissociation, reduce the bimolecular recombination, and facilitate charge extraction. The films processed with environmentally friendly solvent 2-methyl-tetrahydrofuran (MeTHF) exhibits more favourable film morphology than those processed from commonly used halogenated solvents. The all-PSC consisting of the high molecular weight N2200 and PTzBI processed with environmentally friendly solvent MeTHF presents a remarkable power conversion efficiency of 9.16%, which is the highest value so far observed for all-PSCs. Of particular interest is that the PCE remains 6.37% with the active layer thickness of 230 nm. These obervations imply the great promise of the developed all-PSCs for practical applications toward high throughput roll-to-roll technology.
Article
A great advantage of conjugated polymers is the solution processability with low cost. As conjugated polymers typically have flexible alkyl side chains for solubility in organic solvents, J. Liu, L. Wang, and co-workers report in their Communication (DOI: 10.1002/anie.201602775) soluble conjugated polymers bearing novel side chains, branched oligo(ethylene glycol). These polymers can be used in solution-processed polymer solar cells with high efficiency and near-IR response.
Article
Conjugated polymers are essential for solution-processable organic opto-electronic devices. In contrast to the great efforts on developing new conjugated polymer backbones, research on developing side chains is rare. Herein, we report branched oligo(ethylene glycol) (OEG) as side chains of conjugated polymers. Compared with typical alkyl side chains, branched OEG side chains endowed the resulting conjugated polymers with a smaller π-π stacking distance, higher hole mobility, smaller optical band gap, higher dielectric constant, and larger surface energy. Moreover, the conjugated polymers with branched OEG side chains exhibited outstanding photovoltaic performance in polymer solar cells. A power conversion efficiency of 5.37 % with near-infrared photoresponse was demonstrated and the device performance could be insensitive to the active layer thickness.
Article
We synthesize and systematically study a series of conjugated polymers with oligo(ethylene glycol) (OEG) or alkyl chain as the side chain and poly[2,7-fluorene-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] as the polymer backbone. Replacing alkyl chain with OEG chain can decrease the π-π stacking distance of polymer backbone in thin film from 0.44 to 0.41 nm because OEG chain is more flexible than alkyl chain. As the result, the conjugated polymer with OEG side chain exhibits higher hole mobility, red-shifted absorption spectrum in thin film and smaller bandgap than those of the conjugated polymer with alkyl side chain. With the increase of the length of OEG side chain, the resulting conjugated polymers exhibit unchanged π-π stacking distance and decreased hole mobility. Moreover, owing to the large polarity of OEG chain, OEG side chain makes the conjugated polymer suitable for polymer solar cell (PSC) devices processed with polar nonhalogenated solvent, methoxybenzene. A power conversion efficiency of 4.04% is demonstrated with the resulting PSC devices. This work provides the new insight into the effect of OEG side chain on conjugated polymer, which can be used in the molecular design of novel conjugated polymer materials with excellent optoelectronic device performance. (Chemical Equation Presented).
Article
A novel BDT-based conjugated polymer, PBDTTT-S-TEG, and a series of new fullerene derivatives were designed, synthesized and applied to green solvent processable polymer solar cells. By rationally screening processing solvents, a PCE of 4.50% was firstly achieved with definitely low toxic, non-halogenated and safe solvent fabrication, which is almost identical to that processed with o-dichlorobenzene.
Article
High-efficiency bulk heterojunction (BHJ) organic solar cells with power conversion efficiencies of more than 5 % can be fabricated using the green solvent 2-MeTHF. The active layers comprise a blend of a molecular semiconductor donor with intermediate dimensions (X2) and the soluble fullerene derivative [6,6]-phenyl-C61 -butyricacidoctylester (PC61 BC8 ). A switch of the processing solvent from chloroform to 2-MeTHF leads to no negative impacts on the morphology and charge-transport properties of optimally performing BHJ films. Examinations by absorption spectroscopy, atomic force microscopy, and grazing incidence wide-angle X-ray scattering reveal no significant modification of morphology. These results show that green solvents can be excellent alternatives for large-area printing of high-performance organic photovoltaics (OPVs) and thus open new opportunities for sustainable mass production of organic solar cells and other optoelectronic devices.
Article
Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure-property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by mass production technologies.
Article
The molecular weight (MW) of PBnDT-FTAZ can be precisely controlled by adjusting the stoichiometric ratio of two monomers, following the Carothers equation. Study of a set of PBnDT-FTAZ with different MW reveals that the MW significantly influences the morphology and structural order of PBnDT-FTAZ in its bulk heterojunction solar cells, with the highest efficiency (over 7%) achieved with the use of a MW of 40 kg/mol.
Article
Two new 5,6-difluorobenzotriazole (FBTA)-oligothiophene copolymers PFBTA-3T and PFBTA-4T, comprising terthiophene (3T) and quaterthiophene (4T) on the backbone, respectively, were successfully synthesized. A new route to synthesize FBTA monomer was established. Polymers PFBTA-3T and PFBTA-4T exhibited good solubility in common organic solvents and good thermal stability. In comparison to poly (3-hexylthiophene), the incorporations of the FBTA as in PFBTA-3T and PFBTA-4T could result in smaller band gaps around 1.83 eV for the two copolymers. The HOMO levels of PFBTA-3T and PFBTA-4T were -5.49 and -5.31 eV, respectively, while their LUMO levels were -3.65 and -3.90 eV, respectively. In field-effect transistors fabricated without high temperature thermal annealing, PFBTA-3T and PFBTA-4T could display hole mobilities of 1.68 x 10(-3) and 1.31 x 10(-2) cm(2) V-1 s(-1), respectively. The mobility for PFBTA-4T is the highest among the reported FBTA-based polymers, suggesting that FBTA is a promising heterocycle to construct polymers with high mobility. Polymer solar cells were also fabricated with PFBTA-3T and PFBTA-4T as the donor and PC61BM as the acceptor. With copolymer: PC61BM = 1:1.5 as the active layers, polymer solar cells showed power conversion efficiencies of 3.0% and 2.51% for PFBTA-3T and PFBTA-4T, respectively.
Article
Using an environmentally friendly solvent, N-methyl-2-pyrrolidone, PBDTTT-TEG, a polymer with benzodithiophene (BDT) and thieno[3,4-b]thiophene (TT) monomers and triethylene glycol monoether (TEG) side chains chains, can be processed into an active layer for a polymer solar cell (PSC). Combined with phenyl-C71 -butyric acid methyl ester (PC71 BM) as the acceptor, the resulting PSC has a power conversion efficiency (PCE) of 5.23%. This is the first example of an efficient polymer solar cells fabricated from non-aromatic and non-chlorinated solvent.
Article
Water/alcohol-soluble conjugated polymers (WSCPs) and small molecules (WSCSs) are materials that can be processed from water or other polar solvents. They provide good opportunities to fabricate multilayer organic optoelectronic devices without interface mixing by solution processing, and exhibit a promising interface modification ability for metal or metal oxide electrodes to greatly enhance the device performance of solar cells. Moreover, owing to their intriguing processability, WSCPs and WSCSs have great potential for applying environmentally friendly processing technologies to fabricate solar cells. In this review, the authors give an overview of recent developments in WSCPs and WSCSs, including their molecular design, material synthesis, functional principles and application as interface modification layers and photoactive components in emerging photovoltaic technologies such as organic/polymer solar cells, organic-inorganic hybrid solar cells and dye-sensitised solar cells.
Article
Solvents define a major part of the environmental performance of processes in chemical industry and also impact on cost, safety and health issues. The idea of ''green'' solvents expresses the goal to minimize the environmental impact resulting from the use of solvents in chemical production. Here the question is raised of how to measure how ''green'' a solvent is. We propose a comprehensive framework for the environmental assessment of solvents that covers major aspects of the environmental performance of solvents in chemical production, as well as important health and safety issues. The framework combines the assessment of substance-specific hazards with the quantification of emissions and resource use over the full life-cycle of a solvent. The proposed framework is demonstrated on 26 organic solvents. Results show that simple alcohols (methanol, ethanol) or alkanes (heptane, hexane) are environmentally preferable solvents, whereas the use of dioxane, acetonitrile, acids, formaldehyde, and tetrahydrofuran is not recommendable from an environmental perspective. Additionally, a case study is presented in which the framework is applied for the assessment of various alcohol-water or pure alcohol mixtures used for solvolysis of p-methoxybenzoyl chloride. The results of this case study indicate that methanol-water or ethanol-water mixtures are environmentally favourable compared to pure alcohol or propanol- water mixtures. The two applications demonstrate that the presented framework is a useful instrument to select green solvents or environmentally sound solvent mixtures for processes in chemical industry. The same framework can also be used for a comprehensive assessment of new solvent technologies as soon as the present lack of data can be overcome.
Article
Synthese von Benzo[1,2-b:4,5-b′]dithiophen und seinen 4,8-Dimethoxy- und 4,8-Dimethyl-Derivaten Eine einfache Synthese für Benzo[1,2-b:4,5-b′]dithiophen (4) und die Synthese seines bisher unbekannten 4,8-Dimethoxy- (7) und 4,8-Dimethylderivates (13) wird beschrieben. IR-, 1H-NMR-, UV- und MS-Daten werden mitgeteilt.
Article
2-Methyltetrahydrofuran (MeTHF) is a commercially available solvent that is produced from renewable resources. The properties of MeTHF place it between tetrahydrofuran (THF) and diethyl ether in solvent polarity and Lewis base strength. In many cases, MeTHF can replace THF in organometallic reactions. The formation and reaction of Grignard reagents in MeTHF and THF are similar. MeTHF can be used as a solvent for low-temperature lithiation, for lithium aluminum hydride reductions, for the Reformatsky reaction, and for metal-catalyzed coupling reactions. MeTHF is also a good substitute for dichloromethane in biphasic reactions.
Article
Recent research advances on conjugated polymers for photovoltaic devices have focused on creating low band gap materials, but a suitable band gap is only one of many performance criteria required for a successful conjugated polymer. This work focuses on the design of two medium band gap (~2.0 eV) copolymers for use in photovoltaic cells which are designed to possess a high hole mobility and low highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. The resulting fluorinated polymer PBnDT-FTAZ exhibits efficiencies above 7% when blended with [6,6]-phenyl C(61)-butyric acid methyl ester in a typical bulk heterojunction, and efficiencies above 6% are still maintained at an active layer thicknesses of 1 μm. PBnDT-FTAZ outperforms poly(3-hexylthiophene), the current medium band gap polymer of choice, and thus is a viable candidate for use in highly efficient tandem cells. PBnDT-FTAZ also highlights other performance criteria which contribute to high photovoltaic efficiency, besides a low band gap.
Article
Ein leistungsfähiges Polymer: Ein fluoriertes Benzothiadiazol wurde in ein Polymer eingebaut, das in einer Hochleistungssolarzelle genutzt wurde. Das Modellpolymer 2 hat niedrigere HOMO- und LUMO-Energieniveaus als sein nichtfluoriertes Analogon 1 und eine ähnliche Bandlücke wie dieses. Ein aus 2 erhaltenes makroskopisches Heteroübergangssystem hat eine Energieumwandlungseffizienz von 7.2 % (5.0 % mit 1).
Polymer Electron Donor Based on Isoindigo Units Bearing Branched
  • X X Chen
  • Z J Zhang
  • J Liu
  • L X Wang
Chen, X. X.; Zhang, Z. J.; Liu, J.; Wang, L. X. A Polymer Electron Donor Based on Isoindigo Units Bearing Branched
Oligo(ethylene glycol) Side Chains for Polymer Solar Cells
Oligo(ethylene glycol) Side Chains for Polymer Solar Cells. Polym. Chem. 2017, 8, 5496−5503.
  • J.-H Kim
  • C E Song
  • I.-N Kang
  • W S Shin
  • Z.-G Zhang
  • Y Li
  • D.-H Hwang
Kim, J.-H.; Song, C. E.; Kang, I.-N.; Shin, W. S.; Zhang, Z.-G.; Li, Y.; Hwang, D.-H. Conventional and Inverted Photovoltaic Cells Fabricated Using New Conjugated Polymer Comprising Fluorinated Benzotriazole and Benzodithiophene Derivative. Bull. Korean Chem. Soc. 2014, 35, 1356−1364.