Synthesis and photovoltaic properties of a star-shaped molecule based on a triphenylamine core and branched terthiophene end groups

A new star-shaped donor-acceptor molecule has been synthesized for application as the donor material in solution-processed bulk-heterojunction organic solar cells (OSCs). The molecule consists of a triphenylamine (TPA) unit as the core and a donor unit with three arms containing benzo[1,2,5]thiadiazole (BT) acceptor units and 5,5’’-dihexyl-2,2′:3′,2″-terthiophene (tTh) end groups. The molecule, denoted S(TPA-BT-tTh), exhibits a broad absorption band in the wavelength range 300-650 nm and high hole mobility of 1.1×10 -4 cm2 V -1 s 1 . An OSC device based on S(TPA-BT-tTh) as donor and [6,6]-phenyl C71 -butyric acid methyl ester (PC 70 BM) as the acceptor (1:3, w/w) exhibited a power conversion efficiency of 2.28% with a short circuit current density of 6.39 mA/cm2 under illumination of AM.1.5, 100 mW/cm2 .     

Metallated conjugation in small-sized-molecular donors for solution-processed organic solar cells

Four metallated conjugated oligothiophenes,S-1,S-2,S-3 and S-4,with platinum(II)aryleneethynylenes as the electron-rich building block were synthesized to investigate their physicochemical and photovoltaic properties.These small molecules possess fairly low-lying HOMO energy levels which match with the LUMO energy level of the electron acceptor PC70BM([6,6]-phenyl-C71-butyric acid methyl ester).Using the simple process of spin-coating solution fabrication technique,S-1:PC70BM(1:4,w/w)based organic solar cells exhibiting a high Voc of 0.913 V,with a PCE value of 0.88%were developed.In contrast,the OSC device based on S-2:PC70BM(3:7,w/w)displayed a higher PCE of 1.59%with a higher Jsc value of 5.89m A cm–2.The device based on S-4:PC70BM(1:4,w/w)exhibited a PCE value of 1.56%,with a Voc of 0.917 V.     

Improved Photovoltaic Performance of MEH-PPV/PCBM Solar Cells via Incorporation of Si Nanocrystals

We have studied the effect of silicon nanocrystals （SiNCs） as a third component on performance of organic bulk heterojunction solar cells composed of poly[2-methoxy,5-（2＇-ethylhexyloxy）-l,4-phenylene vinylene] （MEH- PPV）：[6,6]-phenyI-C61-butyric acid methyl ester （PCBM） blend film. By adding suitable amounts of SiNCs into MEH-PPV：PCBM blend, the device performance such as external quantum efficiency, short circuit current density （Js（）, and power conversion efficiency （PCE） improved. Incorporation of 2.5% SiNCs in the blend led to 13.6% improvement of Jsc, which in turn resulted in 18% improvement of PCE up to 2.28%. The improved performance was mainly due to the improvements both in the charge generation from the interface of MEH-PPV/SiNCs and the charge collection at the cathode.     

Large open-circuit voltage polymer solar cells by poly(3-hexylthiophene) with multi-adducts fullerenes

Polymer solar cells (PSCs) made by poly(3-hexylthiophene) (P3HT) with multi-adducts fullerenes, [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), PC61BM-bisadduct (bisPC61BM) and PC61BM-trisadduct (trisPC61BM), were reported. Electrochemistry studies indicated that PC61BM, bisPC61BM and trisPC61BM had step-up distributional lowest unoccupied molecular orbital (LUMO) energy. PSCs made by P3HT with above PC61BMs show a trend of enlarged open-circuit voltages, which is in good agreement with the energy difference between the LUMO of PC61BMs and the HOMO of P3HT. On the contrary, reduced short-circuit currents (Jsc) were observed. The investigation of photo responsibility, dynamics analysis based on photo-induced absorption of composite films, P3HT:PC61BMs and n-channel thin film field-effect transistors of PC61BMs suggested that the short polaron lifetimes and low carrier mobilities were response for reduced Jsc. All these results demonstrated that it was important to develop an electron acceptor which has both high carrier mobility, and good compatibility with the electron donor conjugated polymer for approaching high performance PSCs.     

聚合物:富勒烯薄膜光伏电池的反常高温热稳定性研究

聚合物太阳能电池光电转换效率已接近商业化要求,但稳定性差却成为其实用化瓶颈因素.高温暴晒是聚合物太阳能电池实用化必须面临的环境,因此提高聚合物太阳能电池的热稳定性至关重要.本文以典型的Poly(3-hexylthiophene-2,5-diyl(P3HT):[6,6]-Phenyl-C61-butyric acid methyl ester(PC61BM)基聚合物太阳能电池为研究模型,考察其在不同加热温度下(50~110℃)持续工作时的器件效率变化行为,结果发现电池在高温下表现出一种非常规的性能衰减再回升的行为,具体表现为高温下电池首先表现指数式急速衰减(20%~25%),随后发生反常的性能快速恢复至接近初始效率,之后电池保持超长的高温稳定性.光学显微镜和激光光束诱导电流成像结果证明,顶电极覆盖可以有效抑制活性层中PC61BM的聚集结晶,因而电池的反常热诱导稳定性提升与PC61BM的大量聚集结晶无关.活性层薄膜的紫外可见吸收光谱和器件外量子效率的表征结果证明,持续高温加热没有促进PC61BM二聚体的形成,反而有利于PC61BM二聚体的解离.综合实验分析结果,推测PC61BM在光照下的快速二聚反应及其高温解离是导致电池表现出反常热稳定性提升行为的主要原因.实验结果揭示了初期制备的聚合物太阳能电池实际处于一种亚稳态,对器件进行短暂的前期热退火有利于稳定活性层结构,消除亚稳态,有效提升器件稳定性.本研究工作不仅对富勒烯基聚合物太阳能电池的热诱导反常稳定性提升机理机制给出了解释,而且提供了一种提高聚合物太阳能电池稳定性的新策略.     

MEH-PPV和PCBM共混体系光电池中电荷传输及性能与光强的关系

以MEH-PPV{poly[2-methoxy-5-(2'-ethylhexoxy)]-1,4-phenylene vinylene}作为电子给体材料, PCBM[1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61]作为电子受体材料, 制成了共混体系的高性能太阳电池. 光电池在100 mW/cm2强度光照下, 其开路电压Voc为0.8 V, 短路电流密度Jsc为5.06 mA/cm2, 填充因子FF为48.1%, 能量转换效率η为1.93%. UV-Vis及PL图表明, MEH-PPV与PCBM之间没有发生化学变化, 但有明显的荧光猝灭, 说明光生激子能有效地快速分离, 并在各自的传输网络中传递. 分析了光照及暗导I-V曲线的物理意义, 探讨了MEH-PPV与PCBM之间的电荷传输, 研究了在不同强度的光照下器件性能的变化. 随着光强的增加, 器件的短路电流密度线性增大, 开路电压也略有升高, 并联电阻和填充因子下降, 串联电阻变化不明显. 分析了其物理机理, 并进行了合理的解释.     

Study on the Chemical Constituent from the Seed of Litchi chinensis Sonn.

Seed of Litchi chinensis Sonn. is a traditional Chinese medicine, having curative effects on gastric disease, diabetes,and relieving pain.[1] Two new compounds 4-O-p-coumaroylquinic acid butyl ester (1) and 3-O-p-coumaroylquinic acid butyl ester (2), along with five known compounds: 5-O-p-coumaroylquinic acid butyl ester (3),[2] 3-O-p-coumaroylquinic acid methyl ester (4),[3] n-butyl-1-β-D-fructopyranoside (5),[4] D-1-O-methylmyo-inositol (6)[5] and 1H-imidazole-2,3-dihydro-2-oxo-4-carboxylic acid methyl ester (7)[5] were isolated and purified from the ethanol extracts of the seed of L.chinensis Sonn. Their structures, shown in Figure 1, were elucidated by ESI-MS, 1H NMR and 13C NMR, including 2DNMR spectroscopy.     

基于萘[1,2-c:5,6-c]二[1,2,5]噻二唑共轭聚合物的高效光探测器

利用基于萘[1,2-c:5,6-c]二[1,2,5]噻二唑共轭聚合物(NTOD)为给体, 富勒烯衍生物PC71BM为受体, 制备本体异质结聚合物光探测器. NTOD与PC71BM 的共混薄膜吸收范围为300 ~ 830 nm. 通过 对NTOD:PC71BM活性层厚度的调控实现器件暗电流密度的显著降低,增强了探测器的二极管性能,同时保持较高的外量子转化效率. 当活性层厚度为385 nm时,聚合物光探测器在?0.1 V偏压下的暗电流为6.69 × 10–10 A cm?2. 在–0.1 V偏压下器件在440 ~ 800 nm的工作波段的比探测率均超过1013 cm Hz1/2 W?1,处于750 nm的工作波长下达到最大比探测率为1.50 × 1013 cm Hz1/2 W?1,光响应率为0.22 A W?1,这些结果表明基于NTOD:PC71BM的有机光探测器具有广阔的应用前景.     

Efficient P3HT:PC61BM solar cells employing 1,2,4-trichlorobenzene as the processing additives

The efficiency of the poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl C_(61)-butyric acid methyl ester(PC_(61)BM) based organic solar cells was enhanced by using 1,2,4-trichlorobenzene(TCB) as a processing additive to control the blend morphology. The addition of TCB improved the arrangement of P3HT which resulted in good phase separated blend films. Correspondingly, the optimized solar cells showed a power conversion efficiency(PCE) of 4.17% with a fill factor(FF) of 0.69, which were higher than those of common thermal annealing devices(PCE 3.84%, FF 0.67). The efficiency was further improved to 4.74% by thermal annealing at 150 °C for 10 min with a higher FF of 0.74.     

新型酞菁-苝分子异质结的合成及其光伏性能研究

通过酰胺键将酞菁(电子给体单元)和苝二酰亚胺(电子受体单元)偶联,合成了新型的酞菁-苝分子异质结,其在二氯甲烷、氯仿、四氢呋喃等常用溶剂中有较好的溶解度.紫外光谱分析表明其吸收光谱是酞菁和苝二酰亚胺信号的叠加,出现在300～780 nm之间.该分子摩尔消光系数高达105L mol-1 cm-1数量级,说明具有较宽的太阳光谱覆盖范围和很高的吸光系数.基于这些良好的光谱响应特性,制备了以该分子与[6,6]-苯基-C61-丁酸酸甲酯(PC61BM)为光活性层的有机太阳能电池(OSCs),该电池器件结构为ITO/聚(3,4-乙撑二氧噻吩):聚苯乙烯磺酸(PEDOT:PSS)/酞菁-苝给受体分子:PC61BM/Ca/Al,光电转换效率(PCE)为0.009%,对应的开路电压(Voc)为0.472 V,短路电流(Jsc)为0.104 mA/cm2,填充因子(FF)为0.18.     

Fullerene derivative acceptors for high performance polymer solar cells

Polymer solar cells (PSCs) are composed of a blend film of a conjugated polymer donor and a soluble fullerene derivative acceptor sandwiched between a PEDOT?:?PSS coated ITO positive electrode and a low workfunction metal negative electrode. The conjugated polymer donor and the fullerene derivative acceptor are the key photovoltaic materials for high performance PSCs. For the acceptors, although [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) and its corresponding C(70) derivative PC(70)BM are dominantly used as the acceptors in PSC at present, several series of new fullerene derivatives with higher-lying LUMO energy level and better solubility were reported in recent years for further improving the power conversion efficiency of the PSCs. In this perspective paper, we reviewed the recent research progress on the new fullerene derivative acceptors, including various PC(60)BM-like C(60) derivatives, PC(60)BM bisadduct, PC(70)BM bisadduct, indene-C(60) bisadduct and indene-C(70) bisadduct, trimetallic nitride endohedral fullerenes and other C(60) derivatives with multi side chains. The synthesis and physicochemical properties of PC(60)BM and PC(70)BM were also introduced considering the importance of the two fullerene acceptors.     

High performance low band gap polymer solar cells with a non-conventional acceptor

A novel C70 fullerene derivative was designed and synthesized by [4+2] cyclic addition reaction between indene derivative (methyl 1H-indene-3-carboxylate) and C70. The absorption and photoluminescence of H120 and its mixed films with different polymer donor materials were investigated, as well as its electrochemical property and electron mobility. It was found that H120 has 0.05 eV higher LUMO level than that of PC(70)BM. Its electron mobility reached 6.32 × 10(-4) cm(2) V(-1) s(-1), which is slightly lower than 9.55 × 10(-4) cm(2) V(-1) s(-1) of PC(70)BM. The photovoltaic devices based on P3HT, and two high efficiency low band gap polymers, PBDTTT-C and PBDTTDPP as donors, with H120 as an acceptor gave power conversion efficiencies of 4.2%, 6.0% and 6.2%, respectively.     

Absorption spectrophotometric study of supramolecular complexation of [60]- and [70]fullerenes with 24,26-dimethoxy-25,27-dihydroxy calix[4]arene

Supramolecular interactions of 24,26-dimethoxy-25,27-dihydroxy calix[4]arene (1) with [60]- and [70]fullerenes have been studied in only chloroform and in a ternary solvent mixture comprising of chloroform, ethyl alcohol and toluene by UV-vis absorption spectrophotometric method. The experimental results are explained using the model that takes into account the interaction between electronic subsystems of 1 and fullerene. The most interesting feature is the preference of [60]fullerene over [70]fullerene for 1 in ternary solvent mixture as revealed by higher value of formation constant of [60]fullerene/1 complex. The selectivity towards [60]fullerene opens up the way toward self-assembling systems and new separation and purification methods for fullerenes.     

Dihydronaphthyl-based [60]fullerene bisadducts for efficient and stable polymer solar cells

Dihydronaphthyl-based [60]fullerene bisadduct derivative, NC(60)BA, was synthesized at mild temperature in high yield. NC(60)BA not only possesses a LUMO energy level 0.16 eV higher than PC(61)BM but also has amorphous nature that can overcome thermal-driven crystallization. The fabricated P3HT:NC(60)BA-based polymer solar cells exhibit superior photovoltaic performance and thermal stability compared to PC(61)BM-based devices under the same conditions.     

叠氮烷烃环加成反应合成C60衍生物及其聚合物太阳电池的特性

通过烷基叠氮化合物与C₆₀的环加成反应合成了一系列以长链烷烃取代C₆₀的亚氨基衍生物,研究了其紫外-可见光吸收特性及电化学性质,并考察了由这些材料和聚[2-甲氧基-5-(2-乙基己氧基)-1,4-对苯乙炔](MEH-PPV)制成的聚合物光电池的性能.这类器件的能量转换效率介于0.13～0.37之间,随着所接烷基链的增长和支链数目的增加,衍生物的溶解度逐步提高,器件的短路电流随着衍生物溶解度的提高而增加,最高可达到1.77mA/cm²,这类器件具有较极大的光暗比,有可能首先在传感器方面得到应用.     

A scalable synthesis of methano[60]fullerene and congeners by the oxidative cyclopropanation reaction of silylmethylfullerene

1,2-Dihydromethano[60]fullerene and its congeners have attracted much interest, but they have been synthesized only in very low yields because of several insurmountable problems. A new three-stage synthesis involving addition of a silylmethylmagnesium chloride to [60]- and [70]fullerene and oxidation of the anionic intermediate with CuCl(2) afforded the methano[60]- and methano[70]fullerenes in 90% and 70% overall yield, respectively. The reaction with 1,4-diorgano[60]fullerene also proceeded smoothly to give a diastereomerically pure 56-π-electron fullerene that has a higher LUMO level than the parent fullerene and gave a higher open-circuit voltage and better power conversion efficiency when fabricated into an organic photovoltaic device.     

Ultrafast exciton dissociation followed by nongeminate charge recombination in PCDTBT:PCBM photovoltaic blends

The precise mechanism and dynamics of charge generation and recombination in bulk heterojunction polymer:fullerene blend films typically used in organic photovoltaic devices have been intensively studied by many research groups, but nonetheless remain debated. In particular the role of interfacial charge-transfer (CT) states in the generation of free charge carriers, an important step for the understanding of device function, is still under active discussion. In this article we present direct optical probes of the exciton dynamics in pristine films of a prototypic polycarbazole-based photovoltaic donor polymer, namely poly[N-11'-henicosanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), as well as the charge generation and recombination dynamics in as-cast and annealed photovoltaic blend films using methanofullerene (PC(61)BM) as electron acceptor. In contrast to earlier studies we use broadband (500-1100 nm) transient absorption spectroscopy including the previously unobserved but very important time range between 2 ns and 1 ms, which allows us not only to observe the entire charge carrier recombination dynamics but also to quantify the existing decay channels. We determine that ultrafast exciton dissociation occurs in blends and leads to two separate pools of products, namely Coulombically bound charge-transfer (CT) states and unbound (free) charge carriers. The recombination dynamics are analyzed within the framework of a previously reported model for poly(3-hexylthiophene):PCBM (Howard, I. A. J. Am. Chem. Soc. 2010, 132, 14866) based on concomitant geminate recombination of CT states and nongeminate recombination of free charge carriers. The results reveal that only ~11% of the initial photoexcitations generate interfacial CT states that recombine exclusively by fast nanosecond geminate recombination and thus do not contribute to the photocurrent, whereas ~89% of excitons create free charge carriers on an ultrafast time scale that then contribute to the extracted photocurrent. Despite the high yield of free charges the power conversion efficiency of devices remains moderate at about 3.0%. This is largely a consequence of the low fill factor of devices. We relate the low fill factor to significant energetic disorder present in the pristine polymer and in the polymer:fullerene blends. In the former we observed a significant spectral relaxation of exciton emission (fluorescence) and in the latter of the polaron-induced ground-state bleaching, implying that the density of states (DOS) for both excitons and charge carriers is significantly broadened by energetic disorder in pristine PCDTBT and in its blend with PCBM. This disorder leads to charge trapping in solar cells, which in turn causes higher carrier concentrations and more significant nongeminate recombination. The nongeminate recombination has a significant impact on the IV curves of devices, namely its competition with charge carrier extraction causes a stronger bias dependence of the photocurrent of devices, in turn leading to the poor device fill factor. In addition our results demonstrate the importance of ultrafast free carrier generation and suppression of interfacial CT-state formation and question the applicability of the often used Braun-Onsager model to describe the bias dependence of the photocurrent in polymer:fullerene organic photovoltaic devices.     

Charge trapping and storage by composite P3HT/PC60BM nanoparticles investigated by fluorescence-voltage/single particle spectroscopy

Fluorescence-voltage/single particle spectroscopy (F-V/SPS) was employed to study exciton-hole polaron interactions and interfacial charge transfer processes for pure poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) and composite P3HT/PC(60)BM NPs in functioning hole-injection devices. F-V/SPS data collected on a particle-by-particle basis reveal an apparent bistability in the fluorescence-voltage modulation curves for composite NPs of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) that is absent for pure P3HT NPs. A pronounced deep trapping of free electrons photogenerated from the composite P3HT/PC(60)BM NPs at the NP/dielectric interface and hole trapping by fullerene anions in composite P3HT/PC(60)BM NPs under photoexcitation lies at the basis of this finding. The deep electron trapping effect reported here for composite conjugated polymer/fullerene NPs presents an opportunity for future application of these NPs in nanoscale memory and imaging devices.     

CdSe纳米晶/共轭聚合物太阳电池的制备与性能研究

采用有机金属液相法制备了平均粒径为5 nm的CdSe纳米微球(ns-CdSe), 并将其与共轭聚合物(MEH-PPV或P3HT)共混制备了太阳电池器件. 透射电镜(TEM)、紫外-可见吸收光谱(UV-Vis)及荧光光谱(PL)研究结果表明, CdSe纳米晶呈均匀的球状颗粒, 在近红外区具有良好的吸收和荧光性能; 加入CdSe纳米晶能够有效地淬灭共轭聚合物的荧光. 在AM1.5模拟太阳光(光强为100 mW/cm2)照射下, ns-CdSe/MEH-PPV共混体系太阳电池器件性能测试结果为: 短路电流ISC为1.56 mA/cm2, 开路电压VOC为0.75 V, 填充因子FF为34.5％, 光电转换效率η为0.40%; 对于ns-CdSe/P3HT共混体系, 其ISC为1.93 mA/cm2, VOC为0.65 V, FF为38.4%, η为0.48%.     

Influence of the Nanoscale Morphology on the Photovoltaic Properties of Fullerene/MEH-PPV Composites

The relation between morphology and photoelectric properties of PPV derivatives/fullerene composites forming bulk heterojunction solar cells has been investigated. The solvent used to spin cast the photoactive layers has a main influence on the quenching of the MEH-PPV fluorescence, which could be attributed to different dispersion abilities of C₆₀ in the polymer layer shown by AFM microscopy. Formation of large fullerene aggregates is observed at fullerene concentrations of the order of 10% leading to phase separation for composite layers processed in THF, whereas more dispersed distributions of fullerenes are observed in an aromatic solvent like ODCB which accounts for a more efficient luminescence quenching with increasing filler concentrations. However the improvement of the dissociation of photogenerated charge pairs is counterbalanced by a less efficient charge transport in the composite shown by lower short circuit currents probably due to unfavorable polymer chain arrangement in ODCB. Thin film processing conditions have been modified by the preparation of blends of solutions of the polymer in THF and fullerene in ODCB. The resulting spin casted layers show improved morphologies implying better dispersion of the fullerenes and increased short circuit currents. The improvement of the photovoltaic properties of the MEH-PPV/C₆₀ composites has been attributed to the nanosized fullerene domains formed upon phase separation.