Dioctylfluorene‐thiophene based conjugated copolymers for bulk heterojunction solar cells and enhanced power conversion efficiency via methanol treatment

Sensible design and synthesis of conjugating polymers is important to the development of polymer solar cells (PSCs). In this work, we synthesized and characterized two dioctylfluorene‐thiophene based conjugated copolymers, PFTDPP and PFTpBT, having different acceptor groups on the backbone. The photovoltaic properties of the copolymers blended with 6,6‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) as an electron acceptor were obtained. The PSC based on a conventional device configuration ITO/PEDOT:PSS/ Polymer:PC₆₁BM/LiF/Al showed power conversion efficiencies (PCEs) of 2.42% and 3.02% for PFTDPP and PFTpBT, respectively. Methanol treatment was introduced to further optimize device performance, and the solvent treatment gave a dramatic increase in PCE. The best PCEs could reach 4.25% and 4.20% after methanol treatment under AM 1.5G illumination with an intensity of 100 mW cm^?2 from a solar simulator. © 2015 Society of Chemical Industry     

有机无机杂化太阳能电池研究进展

简要介绍了有机无机杂化太阳能电池的结构及原理,以及激子的产生、分离及电荷的传输过程,综述了基于Cd基化合物纳米晶的杂化电池、Pb基化合物纳米晶的杂化电池以及其它半导体纳米晶的杂化电池的研究进展,并指出它们的优缺点和改进有机无机杂化电池性能的研究方向.     

Effects of thiophene units on substituted benzothiadiazole and benzodithiophene copolymers for photovoltaic applications

Two conjugated copolymers, poly{4,7-[5,6-bis(octyloxy)]benzo(c)(1,2,5)thiadiazole-alt-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:3,4-b]dithiophene} ( P1 ) and poly(2-{5-[5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo(c)(1,2,5)thiadiazol-7-yl] thiophen-2-yl}-4,8-di(2-ethylhexyloxyl)benzo(1,2-b:3,4-b)dithiophene) ( P2 ), composed of benzodithiophene and 5,6-dioctyloxybenzothiadiazole derivatives with or without thiophene units were synthesized via a Stille cross-coupling polymerization reaction. These copolymers are promising for applications in bulk heterojunction solar cells because of their good solubility, proper thermal stability, moderate hole mobility, and low band gap. The photovoltaic properties of these copolymers were investigated on the basis of blends of the different polymer/(6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) weight ratios under AM1.5G illumination at 100 mW/cm². The device with indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/ P2: PC₇₁BM (1 : 2 w/w)/Ca/Al gave a relatively better photovoltaic performance with a power conversion efficiency of 1.55%. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

聚合物太阳能电池及材料研究进展

太阳能的充分应用是解决目前人类所面临的能源短缺和环境污染的根本途径。聚合物太阳能电池作为第三代太阳能光伏技术已得到二十多年的研究,其太阳能转化效率已超过10%。回顾聚合物太阳能电池的发展历史和理论研究,太阳能电池的材料与结构对太阳能电池的效率影响很大,尤其是给体材料。从PPV类材料到PT类材料再到PCDTBT、TTBDT、BDTTPD等能级调节后的受体材料,每一次材料的升级,都能让聚合物太阳能电池的效率大幅提高。在聚合物太阳能电池的理论逐渐认识清楚,聚合物太阳能电池制作工艺不断成熟的情况下,研究新型给体材料对向聚合物太阳能电池实用化迈进尤为重要。     

Dinaphtho-s-indacene-based copolymers for inverted organic solar cells with high open-circuit voltages

We report on the synthesis and characterization of a series of donor–acceptor copolymers (PF1, PF2, PF3 or PF4) based on a dinaphtho-s-indacene (DNI) donor unit and four different acceptor units. The molecular weights of the copolymers were determined by using gel permeation chromatography, and their electrochemical properties were investigated by cyclic voltammetry. All four copolymers showed deep-lying highest occupied molecular orbital energy levels. Inverted bulk heterojunction solar cells were fabricated by using the synthesized copolymers as the electron donor material and 6,6-phenyl-C71-butyric acid methyl ester (PC₇₁BM) as the electron acceptor material. Inverted solar cells based on PF1:PC₇₁BM (1:4, w/w) exhibited a power conversion efficiency (PCE) of 3.07%, a high open-circuit voltage (V_oc) of 0.99 V, a short-circuit current density (J_sc) of 7.85 mA/cm², and a fill factor of 39.5% under the AM1.5G illumination. With the same fabrication method, the inverted devices based on PF2, PF3 and PF4 showed PCEs of 2.62, 1.18 and 1.32%, and V_oc values of 0.97, 0.91 and 0.80 V, respectively.     

Synthesis of triarylamine-based alternating copolymers for polymeric solar cell

Two donor-acceptor alternating copolymers based on electron-rich triarylamine, di(1-(6-(2-ethylhexyl))naphthyl)phenylamine (DNPA), and electron-deficient benzothiadiazole and benzoselenadiazole derivatives were designed and synthesized via Suzuki coupling reaction. The resulting triarylamine-based alternating copolymers PDNPADTBT and PDNPADTBS showed good solubility in common organic solvents and good thermal stability. The optical band gaps determined from the onset absorption were 1.93 and 1.81 eV, respectively. By introducing the naphthalene ring into the triarylamine, copolymers had relatively deep HOMO energy levels of −5.48 and −5.45 eV, which led to a high open circuit voltage (V_oc) and good air stability for photovoltaic application. Bulk heterojunction solar cells were fabricated with a structure of ITO/PEDOT-PSS/copolymers-PC₇₀BM/LiF/Al by blending the copolymer with PC₇₀BM. Both blend systems showed remarkably high V_oc near 0.9 V, and the highest performance of 2.2% was obtained from PDNPADTBT, with V_oc = 0.88 V, J_sc = 7.4 mA/cm², and a fill factor of 34.4% under AM 1.5 G.     

Photostability of organic materials used in polymer solar cells

To make polymer solar cells (PSCs) a competitive market technology, integrated efforts are required toward the development of highly efficient light harvesting and charge transporting materials with good thermal and photochemical stability, and which can be processed from solution. Nowadays, a critical issue to be solved is enhancing the stability and durability of PSCs. Indeed, the photoactive material used in the active layer dictates the efficiency of the device on the one hand but, on the other hand, it is well known that organic materials are unstable when exposed to light irradiation, which provokes a degradation of their properties. Making long lifetime solar cells with polymers that are susceptible to degradation under light exposure could be an unrealistic challenge. Therefore, elucidating the mechanism of polymer photodegradation is a key point for developing strategies to decrease or prevent the loss of the functional properties of the material. In this paper, the basic concepts of polymer photo‐aging are explained first. Then the photodegradation mechanisms of conjugated polymers currently used in PSCs are reported. Finally, as barrier materials able to cut off moisture and oxygen ingress are essential for the stability of PSCs, methods for designing coatings for PSC encapsulation are presented, based on recent publications. © 2013 Society of Chemical Industry     

电化学合成含交替苯/噻吩结构的电致变色聚合物

利用Kumada偶联合成了2,5-二苯基噻吩（DPT）、1,4-二噻吩基苯（DTP）及1,4-二（3-甲基-2-噻吩基）苯（DMTP）,并电聚合得到相应的聚合物PDPT、PDTP和PDMTP。PDPT的电化学稳定性较差,而PDTP和PDMTP在0～1.2 V间具有良好的电活性。此外,PDTP和PDMTP分别具有青-橙和红-绿-蓝的电致变色现象,可用于电致变色器件。     

Block copolymers as efficient cathode interlayer materials for organic solar cells

Emerging needs for the large-scale industrialization of organic solar cells require high performance cathode interlayers to facilitate the charge extraction from organic semiconductors. In addition to improving the efficiency, stability and processability issues are major challenges. Herein, we design block copolymers with well controlled chemical composition and molecular weight for cathode interlayer applications. The block copolymer coated cathodes display high optical transmittance and low work function. Conductivity studies reveal that the block copolymer thin film has abundant conductive channels and excellent longitudinal electron conductivity due to the interpenetrating networks formed by the polymer blocks. Applications of the cathode interlayers in organic solar cells provide higher power conversion efficiency and better stability compared to the most widely-applied ZnO counterparts. Furthermore, no post-treatment is needed which enables excellent processability of the block copolymer based cathode interlayer.     

Thiophene‐based copolymers synthesized by electropolymerization for application as hole transport layer in organic solar cells

Electrically conducting thiophene‐based copolymers were synthesized by electropolymerization. The potential range used has a strong influence on the film structure and properties. The extent of oxidation of the copolymers was determined from the ratio of the oxidation to reduction charge, Q_ox/Q_red. The use of wide potential range leads to reduced films, whereas the narrow range leads to partially oxidized films. The copolymers exhibit a characteristic band in UV–vis spectra at ～ 410 nm, which shifts to higher wavelengths for the more doped material. The electrical conductivity of the copolymers was correlated to their morphology and their structure. The copolymer with higher conductivity is partially reduced, has compact morphology and higher ratio of quinoid to benzenoid rings. The energy gap of the copolymers is reversely proportional to their electrical conductivity. The optical and electrical properties of the copolymers make them very well suited for use as hole transport layers (HTL) in organic opto‐electronic devices. We prepared polymer : fullerene solar cells with copolymer HTLs. The solar cell performance was tested with very encouraging initial results. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tailoring side chains of low band gap polymers for high efficiency polymer solar cells

High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schlüter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC₇₁BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.     

Preparation and characterization of alternating copolymers containing fluorene and hexyl‐ or perfluorohexyl‐substituted thiophene

Alternating copolymers containing fluorene and hexyl‐ or perfluorohexyl‐substituted thiophene were synthesized by a palladium‐catalyzed cross‐coupling reaction, and the structures of the polymers were confirmed using nuclear magnetic resonance spectroscopy. The absorption spectra of polymers containing perfluorohexyl substituents show shorter maximum wavelength due to the steric hindrance between fluorene and substituted thiophene units. In addition, the perfluorohexyl substituents can effectively interrupt the conjugation length of the polymers, which leads to an increase in the optical bandgap and decrease in the photoluminescence quantum yield. Solid‐state UV‐visible absorption and emission maxima of the polymers containing perfluorohexyl‐substituted thiophene units are blue‐shifted in comparison to those of polymers in solution due to the packing structure of perfluoroalkyl chains. © 2014 Society of Chemical Industry     

Semitransparent polymer solar cells

Bulk heterojunction based polymer:fullerene solar cells have attracted intensive research interest both in academic and industrial communities in the last two decades, mainly related to their potential low‐cost production process. A power conversion efficiency of over 10% has been reported recently, making the commercialization of this clean and cheap solar energy convertor a realistic prospect for the near future. The intrinsic features of semitransparency and color tunability of the thin polymeric photoactive films are the greatest asset for polymer solar cells. Recently, aesthetic semitransparent polymer solar cells (ST‐PSCs) that can be integrated into transparent windows, roofs, glass and other semitransparent architectural elements have received much attention. In this perspective paper, we present the progress in achieving high performance ST‐PSCs, discuss the requirements for transparent electrodes, focusing on alternatives to tin‐doped indium oxide, and address the challenges ahead to make ST‐PSC viable for real applications. © 2013 Society of Chemical Industry     

Effects of 1,3-dialkylimidazolium cations with different lengths of alkyl chains on the Pt electrode/electrolyte interface in dye-sensitized solar cells

The electrochemical behaviors of the tri-iodide (I₃⁻)/iodide (I⁻) redox couple of symmetric cells were investigated by cyclic voltammetry, steady-state polarization, chronocoulometry, and electrochemical impedance spectroscopy. 1,3-Dialkylimidazolium cations affected the characteristics of the Pt electrode/electrolyte interface by adsorbing on the Pt electrode, as a result of electrostatic interactions, and further affected the reduction of I₃⁻ on the Pt electrode. Capacitance of the double layers of the Pt electrode/electrolyte interface was chiefly determined by capacitance of the compact layer according to the Helmoholtz theory.     

Effect of different electron donating groups on the performance of dye-sensitized solar cells

A series of organic sensitizers containing identical π-spacers and electron acceptors but different, aromatic amine electron-donating groups, were used in dye-sensitized solar cells to study the effect of the electron donating groups on device performance. The derived photophysical and photovoltaic properties, as well as density functional theory calculations, revealed that the tetrahydroquinoline dye was prone to aggregate upon the surface of titanium dioxide owing to the dye's planar structure. A 45% improvement in efficiency of a tetrahydroquinoline dye based cell was achieved when chenodeoxycholic acid was employed as co-adsorbent. However, the airscrew type of triphenylamine unit and Y type structure of the substituted phenothiazine framework suppressed dye aggregation on titanium dioxide. The efficiency of a phenothiazine dye-based cell fabricated using saturated co-adsorbent in dichloromethane was only 15% greater than that achieved in the absence of co-adsorbent. Electrochemical Impedance Spectroscopy was used to determine the interfacial charge transfer process occurring in solar cells that employed different dyes in both the absence and presence of chenodeoxycholic acid as co-adsorbent.     

正丁醇脱氢硫化制备噻吩的研究

采用正丁醇与二硫化碳混合进料脱氢硫化制备噻吩，探讨了两种催化剂体系K₂CO₃-Cr₂O₃/γ-Al₂O₃ 和K₂CO₃/γ-Al₂O₃，对二者进行比较并对活性组分的负载质量分数进行了优选。研究结果表明，在反应条件下n(CS₂)∶n(正丁醇)=2∶1、空速1 h^－1和温度400 ℃，11%K₂CO₃-15%Cr₂O₃/γ-Al₂O₃催化剂在正丁醇合成噻吩的过程中表现较好，目标产物噻吩的收率较高。     

New luminescent 1,2,4-triazole/thiophene alternating copolymers: Synthesis, characterization, and optical properties

New five-membered ring heteroaromatic copolymers composed of 1-alkyl-1H-1,2,4-triazole and thiophene or bithiophene units were prepared by palladium-catalyzed polycondensation. The copolymers were soluble in organic solvents, and showed number-average molecular weights of 6200-23,700 in the GPC analysis. NMR spectroscopy revealed that the copolymers had a regio-random molecular structure. The optical properties, as well as the electrochemical properties, of the copolymers in solutions and films were determined. The polymers exhibited blue photoluminescence (PL) with an emission peak at about 420 nm and quantum yields of 36-43% in solutions, and the PL peak shifted to 470-480 nm in films. X-ray diffraction data suggested that the polymers formed a π-stacked structure in solid state.     

缓冲层在有机太阳能电池中的应用

有机太阳能电池的有机活化层与阴、阳极接触界面的性质对器件性能起着重要的作用。本文综述了近年来有机太阳能电池中使用的阴、阳极界面缓冲材料的类型和工作机制。结果表明,阴、阳极缓冲层的界面修饰对太阳能电池的能量转换效率、寿命和稳定性具有决定性的影响。因此,缓冲层的特性研究对器件结构的改进和性能优化具有一定的指导意义。该研究为其它缓冲层材料在有机太阳能电池中的成功应用提供了有益的实验思路。