Optical, electrical and photovoltaic properties of thermally annealed PPHT:DDE blend thin films

We have investigated the optical, electrical and photovoltaic properties of devices based on 1,2-diazoamino diphenyl ethane (DDE) and poly(3-phenyl hydrazone thiophene) (PPHT):DDE blend. It is observed from the J-V characteristics of the Al/DDE/ITO (ITO—indium tin oxide) device that the electron current injected from Al contact was shown to be space charge limited (SCL), indicating that Al forms nearly ohmic contact for electron injection into lowest unoccupied molecular orbital (LUMO) of DDE. The effect of thermal annealing and composition, on the optical, electrical and photovoltaic response of blend of PPHT and DDE sandwiched between a transparent ITO electrode and an Al back contact are investigated. The observed absorption quenching in the PPHT:DDE blend is attributed to the disordering of PPHT chains and charge transfer between PPHT and DDE as evidenced by FTIR spectra. The observed red shift in the absorption peak on thermal annealing is due to the improvement in the ordering and increases in conjugation length in PPHT. The observed dark current-voltage curves agree well with trap-controlled SCL transport theory. The photophysics of the blend material and influence of thermal annealing on the performance and morphology of these devices were discussed. Annealing process results in the formation of PPHT:DDE complex and increase in the ordering of polymer chain, that increases the incident photon to current efficiency (IPCE) and power conversion efficiency of the photovoltaic devices.     

聚光光伏与温差联合发电装置的研究

针对太阳能量利用率较低的现状,设计了基于砷化镓多结太阳能电池、半导体温差发电片的聚光光伏与温差联合发电装置.通过测量得出单独聚光光伏发电模块在几何聚光比为75时光电转换效率最大,达31.87%;而在加了半导体温差发电模块之后在几何聚光比为112时系统光电转换效率达32.81%,提高了整体光能量转化电能效率.     

溶剂预处理结合热退火提升聚噻吩结晶度及其光伏性能

活性层的微观形貌在很大程度上决定了聚合物光伏器件的性能表现并依赖于制备工艺条件。为了改善薄膜内部分子排布结构并追求较高的器件光电转化效率,采用溶液法制备了基于P3HT：PCBM的聚合物太阳能电池（器件结构:ITO/PEDOT：PSS/P3HT：PCBM/Al）,通过改变器件制备流程中活性层退火处理工艺,研究了热退火、溶剂退火以及溶剂预处理结合热处理的双重退火对聚合物太阳电池性能的影响。研究发现:双重退火的光伏器件的各项性能参数均优于单一退火处理器件,获得了3.25%的光电转化效率。原子力显微镜及X射线衍射仪的表征结果进一步证明:双重退火处理能够在促进聚合物给体良好有序结晶的同时保证共混组分适度地相分离,从而有利于光生激子的解离以及载流子的传输。     

Annealed Treatment Effect in Poly（3-hexylthiophene）：Methanofullerene Solar Cells

Polymer photovoltaic devices based on poly（3-hexylthiophene） （P3HT） ： [6,6]-phenyl-C61-butyricacid methyl ester （PCBM） 1：1 weight-ratio blend are reported. The effects of various annealing treatments on the device performance are investigated. Thermal annealing shows significant improvement of the device performances. For devices at 130℃ annealing, maximum power conversion efficiency （PCE） of 3.3% and All factor up to 60.3% is achieved under air mass 1.5, 100 m W/cm^2 illumination. We discuss the effect of thermal annealing by the results of ultraviolet-visible absorption spectroscopy （UV-vis）, dark current-voltage curve, atomic force microscopy （AFM）.     

有机光伏电池物理性能的模拟

在分析有机聚合物光伏器件物理工作过程的基础上,依据光学原理和扩散理论建立了非相干光吸收模型和激子传输模型. 模拟了限制光伏效率的光学吸收和激子扩散两个主要过程,获得了薄膜厚度与光学吸收、转换效率之间的函数关系,为增强有机薄膜的光学吸收、激子分离与传输并获得高转换效率的有机光伏电池奠定理论基础. 关键词： 有机光伏电池 光学吸收 激子扩散 模拟     

Fabrication and characterization of C60/tetrathiafulvalene solar cells

Fabrication and characterization of C₆₀/tetrathiafulvalene solar cells was carried out. Photovoltaic properties of bulk-hetero and heterojunciotn solar cells were investigated by light-induced current vs. voltage curves and optical absorption. Transmission electron microscopy (TEM) image, X-ray and electron diffraction showed that the bulk-heterojunction film had the microstructure of C₆₀ crystal structure with TTF phase. Heat treatment of the heterojunction film with tetraethylsilane improved the photovoltaic performance, yielding a slight increase of conversion efficiency. This result would be originated in improvement of microstructure around inner interface between the both crystal phases. Mechanisms of the photovoltaic properties were discussed on the basis of the experimental results.     

掺杂CuPc的MEH-PPV/PCBM有机太阳电池研究

采用旋涂法制备了掺杂铜酞菁(CuPc)的聚(2-甲氧基,5-(2-乙基-乙氧基)-对苯乙炔)(MEH-PPV)/ 富勒烯衍生物(PCBM)有机太阳电池. 测试结果表明:掺杂15% CuPc的MEH-PPV/PCBM太阳电池效率(1.41%)比标准的MEH-PPV/PCBM太阳电池(1.26%)提高12%. 器件的吸收谱和迁移率测试表明CuPc导致的吸收谱增强和迁移率提高是器件效率提高的主要原因. 关键词： 有机太阳电池 CuPc掺杂 MEH-PPV/PCBM器件     

新型高效聚合物/富勒烯有机光伏电池研究进展

有机聚合物/富勒烯本体异质结光伏电池以其不断提高的能量转换效率受到了研究人员的广泛关注, 近年来成为光伏电池研究领域的热点之一. 本文主要通过对聚合物/富勒烯太阳能电池的内部机理,包括光吸收、激子扩散和解离以及自由载流子输运和提取等关键科学问题, 从器件材料和结构优化、形貌控制和界面修饰等不同侧面介绍了提高聚合物/富勒烯太阳能电池性能的方法, 讨论了各种器件的结构和能量转换效率, 对于进一步开展这方面的研究工作指明了方向, 最后对其未来的发展前景做出了展望.     

硅BC8量子点太阳能电池中的多重激子效应

多重激子效应是指在纳米半导体晶体中,量子点吸收一个高能光子而产生多个电子-空穴对的过程,该效应可以提高单结太阳电池能量转换效率。利用碰撞电离机制和费米统计模型计算了工作温度300 K的单结硅BC8量子点太阳能电池在AM1.5G太阳光谱下的能量转换效率。对于波长在280~580 nm的入射光,多重激子效应可以大幅增强硅BC8量子点直径d>5.0 nm的量子点太阳电池的能量转换效率。硅纳米量子点的直径d=6.3~6.4 nm时,最大能量转换效率为51.6%。     

退火气压对于P3HT∶PCBM微观形貌及光伏性能的影响

通过精确设定不同的退火环境气压,实现对P3HT(Poly(3-hexylthiophene -2,5-diyl)与PCBM([6,6]-Phenyl C₆₁ butyric acid methyl ester)体系中聚噻吩结晶度以及共混相分离程度的控制,并在此基础上制备了结构为ITO/PEDOT∶PSS/P3HT∶PCBM/Al的正型光伏器件。在允许的压强设定范围内,器件各项性能参数均随退火环境压强的增大表现出先升高后下降的变化规律,并统一于气压设定为1 500 mTorr时获得最大值。从活性层的紫外-可见(UV-Vis)吸收光谱中发现P3HT在510 nm吸收峰以及550和600 nm肩峰附近的吸收强度随退火气压升高而增大,在气压为1 500 mTorr时达到最高,吸收强度的提升源于聚合物分子π—π堆叠的增加。原子力显微镜(AFM)进一步分析结果表明,高气压环境(>1 000 mTorr)能够促进P3HT∶PCBM共混组分在退火过程中形成较大程度的相分离,而当环境压强合适时(1 500 mTorr)适度的相分离利于聚合物形成良好有序结晶,从而能够提升活性层内部载流子传输能力,保证较高的短路电流与填充因子,制备的器件也因此表现出良好的光伏性能,光电转化效率达到3.56%。     

Increasing the quantum efficiency of nickel phthalocyanine films by oxygen adsorption

An examination of the surface photovoltage indicates that when oxygen adsorbs on a nickel phthalocyanine polycrystalline film, one form adsorbs irreversibly with a sticking probability of 9 × 10^?3 and a second form adsorbs reversibly with a sticking probability >0.1. The reversibly adsorbed oxygen can be removed by evacuating the ambient oxygen, while the irreversible form can only be removed by heating the sample to 433 K. The irreversibly adsorbed oxygen causes an order of magnitude increase in the photovoltage, even though a comparison of the photovoltaic relaxation times indicates that this oxygen has actually slightly lowered the energy band bending at the surface depletion layer. This increase in the photovoltage is therefore attributed to an increased quantum efficiency of minority carrier injection in a process which is analogous to that observed for oxygen in the bulk.     

Polymer heterostructures with embedded carbon nanotubes for efficient photovoltaic cells

Polymer photovoltaic cells (PVC) are intensely investigated because of their potential advantages over Si-based PVCs. Their present drawbacks are low conversion efficiency, limited exciton diffusion length, poor hole carriers transport and short lifetime. The highest conversion efficiency achieved so far in spin-coated polymer blends is close to 5%. Recently, efficiency growing has been demonstrated in multilayer architectures involving a donor/acceptor bulk heterojunction. Alternatively, a nanomaterial has been added to the polymer active layer to facilitate excitons dissociation and carriers transport through the polymer matrix. In this work we investigate both these approaches, first embedding single wall Carbon Nanotubes (SWCNT) in the polymeric matrix to improve the electrical transport and second studying the optical absorption of different polymer thin films to optimize the spectral response of the donor/acceptor heterojunction.     

平板集热太阳热电器件建模及结构优化

太阳能热电转换是光伏效应外另一种直接将太阳辐射转变为电能的途径, 近年来已经成为太阳能利用的热点之一. 本文以Bi₂Te₃材料为基础构建平板集热太阳热电器件模型, 采用有限元法分析AM1.5辐射条件下器件温度分布情况, 并结合基于温度的物性参数计算集热比、热臂截面积与长度变化等因素对器件的开路电压、 最大输出功率及转化效率的影响. 研究发现: 集热比与热臂长度的变化对器件性能有显著影响, 热臂截面积的变化对器件转化效率影响相对较弱; 在这一模型中, 平板集热太阳热电器件的转化效率达到1.56%.     

Dye-sensitized solar cell module realized photovoltaic and photothermal highly efficient conversion via three-dimensional printing technology

Three-dimensional(3D) printing technology is employed to improve the photovoltaic and photothermal conversion efficiency of dye-sensitized solar cell(DSC) module. The 3D-printed concentrator is optically designed and improves the photovoltaic efficiency of the DSC module from 5.48% to 7.03%. Additionally, with the 3D-printed microfluidic device serving as water cooling, the temperature of the DSC can be effectively controlled, which is beneficial for keeping a high photovoltaic conversion efficiency for DSC module. Moreover, the 3D-printed microfluidic device can realize photothermal conversion with an instantaneous photothermal efficiency of 42.1%. The integrated device realizes a total photovoltaic and photothermal conversion efficiency of 49% at the optimal working condition.     

Effect of crystalline microstructure on the photophysical performance of polymer／perylene composite films

To obtain high carrier mobility, better charge injection capability, and high photovoltaic device conversion efficiency, a powerful strategy is to improve the morphology of the polymer/dye composite films. Conjugated conducting polymer (CP) thin films doped with perylene derivative (PV) of various concentrations were prepared by spin-casting method, and their morphology and photovoltaic characteristics were examined. The change in morphology and molecular reorientation occurring in CP-PV composite films upon annealing at different temperatures was investigated using scanning electron microscopy, x-ray diffraction, Fourier transform infrared and UV-vis absorption. By changing the annealing temperature, PV microcrystallines of 8－10μm in size lying parallel to the substrate surface can be obtained. Annealing effect improved the photovoltaic performance of ITO/CP-PV/Al Schottky-type solar cells, which can be attributed to the formation of an electron conducting PV crystal network. Preliminary studies indicate that the morphological structure in CP-PV composite films has an important influence to their photovoltaic properties.     

Inverse relation between photocurrent and absorption layer thickness in polymer solar cells

Organic solar cells based on polymer–fullerene bulk heterojunctions were optimised with respect to the short circuit photocurrent by means of optical modelling. Due to interference effects present in the thin film multilayer device, an inverse relation between active layer thickness and photocurrent was predicted and experimentally verified. Optimised photovoltaic devices yield power conversion efficiencies of 4%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology and properties of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) based solar cells

The influence of two components blend ratio, solution concentration and thermal annealing on the morphology of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend films spin-cast from chloroform solutions has been studied using atomic force microscopy (AFM). The AFM images show that the dimension of the phase separation increases with the EP-PTC content and total solution concentration. When the annealing temperature increases from 90 to 150 °C, the EP-PTC crystal-like clusters grow rapidly. Solar cells based on MEH-PPV:EP-PTC blend films with different weight ratios were fabricated. The device with 1:3 weight ratio has a higher power conversion efficiency (PCE) of 0.072% compared with the devices with 1:1, 1:2 and 1:4 ratio, which increases by about 14 times over that of the device with 1:1 ratio that has a PCE of 0.005%. It is indicated that the optimum performance of the photovoltaic device is strongly related to the finer phase separation between MEH-PPV and EP-PTC on a submicron scale which enables an efficient dissociation of photogenerated excitons, and the pure EP-PTC phase can build up a percolating network with pathways large enough to enhance electron transport.     

Improvement of ZnO nanorod-based dye-sensitized solar cell efficiency by Al-doping

The current study investigates the performance of dye-sensitized solar cells (DSSCs) based on Al-doped and undoped ZnO nanorod arrays synthesized by a simple hydrothermal method. Current density-voltage (J-V) characterizations indicate that Al-doping in ZnO crystal structure can significantly improve current densities and the energy conversion efficiency (η) of ZnO nanorod-based DSSCs. The maximum η, 1.34%, was achieved in DSSC when Al-doped ZnO nanorod arrays were grown in 0.04 M zinc acetate dihydrate solution with 5 mM aluminum nitrate nonahydrate. This result represents a large increase of η in Al-doped ZnO nanorod-based DSSCs as compared to undoped (0.05%). The improved DSSC photovoltaic performance can be attributed to two main factors: (1) increased light harvesting efficiency due to a large amount of N719 adsorbed on the large surface area of Al-doped ZnO nanorod arrays, and (2) increased electrical conductivity due to A1³⁺ ion doped into the ZnO lattice at the divalent Zn²⁺ site, allowing electrons to move easily into the Al-doped ZnO conduction band.     

薄膜生长速率对有机光伏器件性能的影响

采用真空热蒸发镀膜的方法制备了酞菁铜(CuPc)和富勒烯(C60)构成的平面异质结结构光伏器件,并初步研究了CuPc薄膜生长速率对器件光伏性能的影响,我们发现以较大薄膜生长速率制备的器件表现出较大的短路电流和能量转换效率。X射线衍射和原子力显微镜观察的结果表明生长速率较大的CuPc薄膜结晶相含量较少,薄膜结构较均匀、致密、平整,这可能使得CuPc薄膜激子扩散和载流子迁移特性得到提高,也可能改善其与C60受主薄膜和ITO阳极的接触,并有利于载流子的分离和收集,从而表现出较好的光伏特性。     

Thermoelectric properties of Bi-Sb semiconducting alloys prepared by quenching and annealing

Bi_100−xSb_x (x=8-17) alloys were prepared by direct melting of constituent elements, which was followed by quenching and annealing. The synthesis of high-homogeneity alloys was confirmed by X-ray diffraction, differential thermal analyses and electron microprobe analysis. The semiconducting and thermoelectric properties of the samples were investigated by measuring Hall coefficient, electrical resistivity and Seebeck coefficient in the temperature range from 20 to 300 K for both the as-quenched and annealing samples. The properties change gradually with the Sb concentration x, which is attributed to the variation of the energy gap. The Hall mobility was enhanced by annealing, which leads to a small electrical resistivity and a large Seebeck coefficient. Consequently, large values of about 8.5 mW/mK² for the power factor were obtained in the annealed alloys of x=8,12, and 14.