The inverted solar cells with the polymer:fullerene blend film possessing a stratified composition profile

The inverted polymer:fullerene solar cells with structure of ITO/TiO₂/P3HT:PCBM/MoO₃/Al have been fabricated, where P3HT and PCBM stand for poly (3-hexylthiophene) and [6,6]-phenyl C₆₁-butyric acid methyl ester, respectively. It is discovered that the P3HT:PCBM blend film manipulated into the improved stratification structure, characterized as P3HT crystallite-rich zone close to the top surface and PCBM constituent-rich zone adjacent to the bottom surface, can offer nearly the same power conversion efficiency of solar cell, compared to the one grown into the bulk heterojunction structure, characterized as the bicontinuous interpenetrating network of P3HT and PCBM. We provide an alternative insight to the morphology control of inverted polymer:fullerene solar cells.     

Photoinduced C70 radical anions in polymer:fullerene blends

Photoinduced polarons in solid films of polymer:fullerene blends were studied by photoluminescence (PL), photoinduced absorption (PIA) and electron spin resonance (ESR). The donor materials used were P3HT and MEH‐PPV. As acceptors we employed PC₆₀BM as reference and various soluble C₇₀‐derivates: PC₇₀BM, two different diphenylmethano‐[70]fullerene oligoether (C₇₀‐DPM‐OE) and two dimers, C₇₀–C₇₀ and C₆₀–C₇₀. Blend films containing C₇₀ revealed characteristic spectroscopic signatures not seen with C₆₀. Light‐induced ESR showed signals at g ≥ 2.005, assigned to an electron localized on the C₇₀ cage. The formation of C₇₀ radical anions also leads to a subgap PIA band at 0.92 eV, hidden in the spectra of C₇₀‐based P3HT and MEH‐PPV blends, which allows for more exact studies of charge separated states in conjugated polymer:C₇₀ blends. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Field-effect transistor structures on the basis of poly(3-hexylthiophene), fullerene derivatives [60]PCBM, [70]PCBM,and nickel nanoparticles

Organic field-effect transistor (OFET) structures with the active layers on the basis of composite films of semiconductor polymer poly(3-hexylthiophene) (P3HT), fullerene derivatives [60]PCBM, [70]PCBM, and nickel (Ni) nanoparticles are obtained, and their optical, electrical, and photoelectrical properties are studied. It is shown that introducing Ni nanoparticles into P3HT: [60]PCBM and P3HT: [70]PCBM films leads to an increase in the absorption and to quenching of photoluminescence of the composite in the 400–600 nm spectral band due to the plasmon effect. In P3HT: [60]PCBM: Ni and P3HT: [70]PCBM: Ni OFET structures at the P3HT: [60]PCBM and P3HT: [70]PCBM concentrations of ~1: 1 and Ni concentrations of ~3–5 wt %, current–voltage (I–V) characteristics typical of ambipolar OFETs with the dominant hole conduction are observed. The charge-carrier (hole) mobilities calculated from the I–V characteristic at V_G =–10 V were found to be ~0.46 cm²/(V s) for P3HT: [60]PCBM: Ni and ~4.7 cm²/(V s) for P3HT: [70]PCBM: Ni, which means that the mobility increases if [60]PCBM in the composition is replaced with [70]PCBM. The effect of light on the I–V characteristics of P3HT: [60]PCBM: Ni and P3HT: [70]PCBM: Ni OFETs is studied.     

The effect of post-annealing on the interface between the aluminum electrode and the active layer in polymer/fullerene solar cells

The post-annealing effects on the performance of poly (3-hexylthiophene) (P3HT)/(6,6)-phenyl C₆₁ butyric acid methyl ester (PCBM) solar cells with conventional bulk heterojunction (CBHJ) and layer-evolved bulk heterojunction (LBHJ) have been compared. It is found that contrary to the much better performance obtained from CBHJ cells, the post-annealing deteriorates the performance of LBHJ devices. Aqueous contact angle and X-ray photoelectron spectroscopy measurements show that P3HT is dominant at the top surface of CBHJ film, while PCBM is dominant at the top surface of LBHJ film. The micron-scale morphology evolution of the active layer/Al interface upon post-annealing reveals that the PCBM-rich surface is beneficial for the nucleation and growth of PCBM crystal, which does harm to the contact between the active layer and the electrode and results in the decrease of the fill factor. However, the original P3HT-rich surface prevents the formation of large surface-segregated PCBM clusters upon post-annealing, which is highly desirable for the efficient polymer/fullerene solar cells.     

Influence of fullerene derivative replacement with TiO2 nanoparticles in organic bulk heterojunction solar cells

In an effort to develop hybrid organic solar cells with improved power conversion efficiency (PCE), devices based on poly (3-hexylthiophene) (P3HT):phenyl C₆₁-butyric acid methyl ester (PCBM) active layer and poly (3,4-ethylenedioxythiophene) (PEDOT):poly (styrenesulfonate) (PSS) buffer layers were prepared. A systematic replacement of PCBM was achieved by introducing nanostructured TiO₂ (∼15 nm particle size), dissolved separately in chlorobenzene (CB) and 1,2 –dichlorobenzene (DCB), to the (P3HT:PCBM) active layer while keeping a fixed amount for P3HT. To understand the effect of fullerene replacement with the inorganic metal oxide nanoparticles on different properties of resulting devices, a variety of techniques such as Current–Voltage (J–V) characteristics, Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Ultravoilet-Visible (UV–Vis) Spectrophotometry and External Quantum Efficiency (EQE) were employed. The addition of TiO₂ nanoparticles in the active layer improved the power conversion efficiency (PCE) of P3HT:PCBM devices. The addition of TiO₂ nanoparticles using CB as solvent enhanced the absorption in visible region and also introduced a red shift in the absorption spectra. A significant increase in EQE was observed for devices with TiO₂ nanoparticles in the active layer. Mixing TiO₂ also increased the surface roughness of the active layer where TiO₂ nanoparticles were found to agglomerate as their concentration increased relative to fullerene derivative. A complete agglomeration of TiO₂ was observed in the absence of PCBM.     

Correlation between spectroscopic and morphological properties of composite P3HT/PCBM nanoparticles studied by single particle spectroscopy

We report the fabrication and characterization of composite nanoparticles consisting of a conducting polymer, poly-3-hexylthiophene (P3HT), doped with varying amounts of [6,6]-phenyl C61-butyric acid methyl ester (PCBM), a material blend that is commonly applied in bulk heterojunction organic photovoltaic devices (OPVs). Single particle spectroscopy (SPS) studies, where nanoparticles are studied one particle at a time, reveal that these nanoparticles have spectroscopic characteristics consistent with the existence of two types of crystalline nanodomains, one with a higher energy emission at 660 nm and one with a lower energy emission at 720 nm. In addition, the occurrence of emission at lower peak energy increases with increasing PCBM doping levels, and the intensity of the lower energy peak emission increases with respect to the higher energy peak emission as well. These data reveal a PCBM concentration dependent formation of two types of P3HT crystalline nanodomains in P3HT/PCBM composite nanoparticles, where the lower energy crystal structure becomes more favored with higher PCBM concentration. This work provides a molecular scale insight in the correlation between changes in morphology of conjugated polymer materials with different weight percentages of fullerene dopants.     

Programming resistive switching memory by a charged capacitor

The performances of bulk-heterojunction (BHJ) solar cells are investigated for time-dependent thermal annealing with different morphology evolution scales, having special consideration for the diffusion and aggregation of fullerene derivative molecules based on blends of poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM). Meaningfully, rapid formation of dot-like and needle-like crystalline PCBM structures of a few micrometers up to 60 μm in size is obtained with thermal annealing treatment from 2 to 15 min, which dynamically reflects a fast process of PCBM molecule and cluster aggregation. Upon ultrasonic-assisted processing and annealing treatment, the scale of P3HT crystals is drastically increased in view of X-ray diffraction (XRD) patterns, leading to a high hole mobility. And, the P3HT domains can be gradually converted into larger P3HT crystals approved by the decreased full width at half-maximum in the XRD patterns. Corresponding current–voltage curves are measured in quantity and we propose a model to explain the effect of the crystalline degree of P3HT domains and aggregation of PCBM molecules and clusters on the phase segregation, expressing a viewpoint towards high performance of BHJ solar cells.     

Charge transport in polythiophene:fullerene:nanotube bulk heterojunction photovoltaic devices investigated by impedance spectroscopy

P3HT:PCBM bulk heterojunction devices incorporating SWNTs, which are predominantly metallic in character, have been analyzed using impedance spectroscopy to understand the effect of SWNTs on their charge carrier transport properties. SWNTs reduce the effective lifetime of injected charge carriers. Frequency dependence of capacitance and conductance of P3HT:PCBM devices show monotonic variations without any clear peak positions. Simulations of the complex admittance of the P3HT:PCBM devices under trap free space charge limited current within the framework of Scher–Montrol theory are used to qualitatively show that such characteristics are a signature of charge transport which is highly dispersive in nature. The position of peak τ_peak in the imaginary part of impedance Im(Z), which is essentially same as the first transition frequency of Cole–Cole plot, has a direct relation with the effective dc mobility of charge carriers which varies with dispersion parameters. Using the dc mobility values and the voltage variation of peak frequency of Im(Z), the ratio of τ_dc to τ_peak has been calculated. The magnitude of this ratio is indicative of the degree of dispersiveness in transport. It has been shown that, SWNTs at low concentrations tend to reduce the dispersiveness in charge transport.     

P3HT:PCBM薄膜成膜过程对聚合物太阳能电池性能的影响

P3HT:PCBM薄膜的快速和缓慢成膜过程能显著的改变异质结聚合物太阳能电池性能.通过调节旋转时间以及薄膜退火前的间隔时间,研究了P3HT:PCBM混合薄膜缓慢生长所需最佳时间.结果表明,在转速800 r·min-1下旋涂薄膜,经过50～80 s的旋涂,接着放置样品薄膜30 min以上,然后再对薄膜进行退火处理,电池效...     

Effect of a buffer layer, composition and annealing on the performance of a bulk heterojunction polythiophene/fullerene composite photovoltaic device

Post-annealing of P3HT/C₆₀-based plastic solar cells, composite ratio and, incorporation of a buffer layers at the ITO–polymer/fullerene composite interface and the polymer/fullerene composite–Al interface have shown significant improvement in the performance of the photovoltaic device, both in terms of open-circuit voltage and short-circuit current. The annealing temperature, time duration and P3HT/C₆₀ composite ratios have been optimized for the best performance of typical ITO/PEDOT:PSS/P3HT:C₆₀/LiF/Al solar cell. The C₆₀ content is very crucial because it improves the photocurrent in the beginning but after a certain value it leads to decrease in absorption, thereby decreasing the photocurrent.     

二甲基亚砜添加剂对聚合物太阳能电池性能的影响

研究了二甲基亚砜(DMSO)掺杂浓度对基于聚(3-己基噻吩)(P3HT)和(6,6)-苯基碳60丁酸甲酯(PCBM)为有源层的聚合物太阳能电池性能影响。结果表明,掺杂DMSO可以提高聚合物太阳能电池短路电流密度和填充因子。DMSO掺杂质量比为3%时,电池短路电流密度提高到7.88 mA·cm-2,填充因子为55.5%。能量转换效率达到2.54％,相比没有掺杂DMSO的电池,能量转换效率提高了17%。傅里叶变换红外光谱被用于鉴定和分析掺杂DMSO对材料P3HT∶PCBM化学性质的影响。傅里叶变换红外光谱表明,掺杂后P3HT和PCBM的化学性质都没有改变。为分析掺杂DMSO改善器件能量转换效率的原因,通过紫外-可见光谱和电流密度-电压特性曲线分别表征器件的光吸收能力以及电致发光器件的载流子迁移率。与P3HT∶PCBM薄膜相比,P3HT∶PCBM∶DMSO薄膜在可见光范围内的吸收峰有明显红移且吸收强度增强。可见光吸收的改善是实现短路电流密度提高的有力保障。太阳能电池性能的增强是因为DMSO的掺杂提高了P3HT∶PCBM的载流子迁移率和吸收光谱宽度。     

热处理对不同溶剂制备的共混体系太阳电池性能影响

本文以poly(3-hexylthiophene) (P3HT)为电子给体材料, -phenyl C₆₁-butyric acid methyl ester (PCBM)为电子受体材料, 制备出不同溶剂形成的共混体系太阳电池.从薄膜的紫外—可见吸收光谱(UV-vis)、光致发光谱(PL)、原子力表面图形(AFM)等方面,分析了热处理对不同溶剂制备的共混体系太阳电池性能的影响.结果表明较高沸点的溶剂有利于P3HT:PCBM共混体系中P3HT的有序化排列,薄膜的紫外—可见吸收和光致发光增 关键词： 热处理 不同溶剂 太阳电池 性能     

Plasmonic effects and the morphology changes on the active material P3HT:PCBM used in polymer solar cells using Raman spectroscopy

There is no consensus yet that the enhancement effects of plasmonic device are predominantly caused by plasmonic effects or induced morphology changes in the optoelectronic `materials. Herein, we present a detailed Raman characterization of a typical organic P3HT:PCBM system comprising silver nanowires (Ag NWs) with different size, which can simultaneously study the plasmonic effects and the morphology changes. The direct comparison of the Raman spectra of non‐annealed and annealed samples indicates that the morphology of plasmonic samples has changed before annealing and the morphology of plasmonic samples and reference sample after annealing is not distinguishable. This indicates that the interaction between P3HT and Ag NWs with different size can be explained by plasmonic effects after annealing. Moreover, in‐situ Raman spectroscopy is used to study the morphology changes in plasmonic samples with different diameters of Ag NWs during heating process. This method can distinguish the plasmonic effects and morphology changes of plasmonic device. Copyright © 2016 John Wiley & Sons, Ltd.     

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%。     

NiO_x作为空穴传输层对有机太阳能电池光吸收的影响

基于多层膜系模型的传输矩阵方法、麦克斯韦方程和光子吸收方程,研究了NiOx作为替代3,4-乙撑二氧噻吩:聚苯乙烯磺酸盐(PEDOT:PSS)的空穴传输材料对聚3-己噻吩(P3HT)和富勒烯衍生物([6,6]-phenyl-C61-butyric acid methyl ester,PC61BM)共混体异质结有机太阳能电池器件内部光电场分布和光吸收特性的影响.分别制备了以NiOx和PEDOT:PSS为空穴传输层,P3HT:PCBM为活性层的有机太阳能电池,并通过数值模拟的方法比较了NiOx和PEDOT:PSS两种空穴传输材料对器件光伏特性的影响.结果表明:10 nm的NiOx空穴传输层器件比40 nm的PEDOT:PSS器件获得了更大的短路电流和填充因子,并具有更高的能量转化效率.     

Organic photovoltaic cells based on conjugated polymer/fullerene composites

We fabricated organic photovoltaic cells using poly[2-methoxy,5-(2^′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and fullerene derivative, [6,6]-phenylen C₆₁-butyric acid methyl ester (PCBM), composites with various concentrations of the PCBM. The devices exhibit photoluminescence quenching and enhancement in photovoltaic response with increasing PCBM concentrations, both of which are associated with the photoinduced charge transfer characteristics of these materials. We also investigate the PCBM concentration dependence on the device performance near the percolation threshold for fullerene derivative charge transport channel, and discuss the role of fullerene interpenetrating networks in these organic photovoltaic cells.     

Improved performance of polymer solar cells by using inorganic,organic, and doped cathode buffer layers

The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester(P3HT:PCBM) polymer solar cell, we studied the effect of the cathode buffer layer(CBL) between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode(OLED) were employed as the CBL in the P3HT:PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs_2CO_3, bathophenanthroline(Bphen), and 8-hydroxyquinolatolithium(Liq) can be used as CBL to efficiently improve the device performance of the P3HT:PCBM polymer solar cells. The P3HT:PCBM devices employed various CBLs possess power conversion efficiencies(PCEs) of 3.0%–3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen:Cs_2CO_3 and Bphen:Liq as the CBL, the PCE of the P3HT:PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL.     

Dual plasmonic‐enhanced bulk‐heterojunction solar cell incorporating gold nanoparticles into solution‐processed anode buffer layer and active layer

A dual plasmonic resonance effect on the performance of poly(3‐hexylthiophene) (P3HT):phenyl C61‐butyricacid methyl ester (PC61BM) based polymer solar cells (PSCs) has been demonstrated by selectively incorporating 25 nm colloidal gold nanoparticles (Au NPs) in a solution‐processed molybdenum oxide (MoO₃) anode buffer layer and 5 nm colloidal Au NPs in the active P3HT:PCBM layer. The devices exhibit up to ～20% improvement in power conversion efficiency which is attributed to the dual effect of localized surface plasmon resonance (LSPR) of Au NPs with enhanced light absorption and exciton generation. Our report shows a guideline on the usage of dual LSPR effect for the solution‐processed polymer solar cells to achieve high efficiencies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Plasmon enhanced light absorption in bulk heterojunction organic solar cells

Silver nanospheres (Ag NSs) buffer layers were introduced via a solution casting process to enhance the light absorption in poly (3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) bulk heterojunction organic solar cells. These Ag NSs, as surface plasmons, could increase the optical electric field in the photoactive layer whilst simultaneously improving the light scattering. As a result, this buffer layer improves the light absorption of P3HT:PCBM blend and consequently improves the external quantum efficiency (EQE) of organic solar cells. In this work, different sizes of Ag NSs plasmon‐enhanced layer were investigated, with the aim of optimizing the performance of devices. UV‐vis spectrometer measurement demonstrates that the total optical absorption of P3HT:PCBM blend films in the spectral range of 350–650 nm is increased by ～4 and 6% with incorporation of the 20 and 40 nm Ag NSs, respectively. The J_sc was shown to increase by ～21 and 24% for 20 and 40 nm Ag NSs, respectively. This is due to the extra photogenerated excitons by the plasmonic resonance of Ag NSs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hybrid polymer/inorganic nanoparticle blended ternary solar cells

Hybrid polymer/inorganic nanoparticle blended ternary solar cells are reported. These solar cells have an active layer consisting of PbS colloidal quantum dots (CQDs), poly (3‐hexylthiophene) (P3HT), and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). Power conversion efficiency (PCE) was improved by incorporating PbS CQDs in the active layer of P3HT:PCBM‐based organic solar cells. As the concentration of PbS CQDs in the hybrid solar cells was increased, PCE was also increased. This improvement resulted from improved charge transfer and also extended light absorption into the near‐infrared. The PCE of the hybrid solar cells was 47% higher than that for reference organic solar cells on average under air mass 1.5 global illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)