【作者】 李蛟；

【导师】 高从堦； 刘俊成；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2010， 博士

【摘要】 目前困扰有机太阳能电池发展的主要问题是器件效率偏低,如何提高它的能量转换效率是其能否商业化和与传统无机光伏电池竞争的关键。本文围绕有机太阳能电池阳极修饰层聚3,4-乙撑二氧噻吩：聚(对苯乙烯磺酸)根阴离子(PEDOT:PSS)薄膜的掺杂改性及其在有机太阳能电池中的应用研究开展了相关工作,主要内容与结论如下：1.采用共混-旋涂法在石英玻片上分别制备出经多壁碳纳米管(MWCNTs)、山梨醇、溴三种掺杂剂掺杂的PEDOT:PSS透明导电膜,研究了不同掺杂剂的加入对薄膜透光性能与导电性能的影响。①在550nm～850nm波段,多壁碳纳米管掺杂使PEDOT:PSS薄膜透光性能有所降低,山梨醇与溴掺杂则有利于PEDOT:PSS薄膜透光性能的提高。②多壁碳纳米管、山梨醇、溴掺杂均可提高PEDOT:PSS薄膜的导电性能。其中,8wt%山梨醇掺杂可以使PEDOT:PSS薄膜的导电能力提高400多倍。6wt%溴掺杂可以使PEDOT:PSS薄膜的导电能力提高近300倍。0.20wt%多壁碳纳米管掺杂可以使PEDOT:PSS薄膜的导电能力提高约40倍。2.根据X射线衍射(XRD),扫描电镜(SEM),原子力显微镜(AFM),X射线光电子能谱(XPS)等检测结果,详细研究了多壁碳纳米管、山梨醇、溴三种掺杂剂的加入与PEDOT:PSS薄膜导电性能变化之间的内在联系。①多壁碳纳米管掺杂PEDOT:PSS薄膜的导电机理可以概括为二种效应,一是“共轭效应”,二是碳管“网络效应”。在多壁碳纳米管微量掺杂阶段(0.04wt%),碳管在薄膜中零星分布,相互之间少有接触,此时,多壁碳纳米管会与PEDOT主链中五元噻吩环发生π-π共轭作用,引起二者之间电子云密度的变化,从而增加了PEDOT主链载流子的离域化程度,有利于薄膜导电性能的提高。当多壁碳纳米管掺杂含量达到0.10wt%时,多壁碳纳米管在薄膜内部形成网络结构,新导电通道形成,有效提高薄膜导电性能。掺杂量超过0.20wt%时,由于碳管相互接触电阻增大,薄膜导电性能开始下降。②山梨醇掺杂PEDOT:PSS薄膜导电机理：山梨醇的加入致使PEDOT主链结构发生发生苯-醌变化。苯式结构的PEDOT分子以无规线团形卷曲状存在,而醌式结构的PEDOT分子表现为伸展形卷曲状或直线状。相比较而言,伸展形卷曲状或直线状链形态中局部有序结构大幅增加,有利于载流子在PEDOT链中的迁移,从而表现为PEDOT:PSS薄膜电导率增加。③溴掺杂PEDOT:PSS薄膜导电机理：溴加入PEDOT:PSS水溶液中,会与水反应生成具有弱氧化性的氢溴酸；同时,溴在水中饱合时,还存在具有弱氧化性的溴分子。二种弱氧化物的存在,对于PEDOT:PSS薄膜会产生二种作用：一是释放更多的电子,使PEDOT主链上空穴载流子浓度增加,增加薄膜导电性能；二是由于其氧化性的存在,对PEDOT的主链结构会有所破坏,降低薄膜导电性能。当第一种效应大于第二效应时,薄膜的导电性能表现为增加；而当第二种效应大于第一种效应时,薄膜的导电性能表现为下降。3.以聚(3-己基噻吩)与1-(3-甲氧基羧基)-丙基-1-苯基-(6,6)C61共混物为光电活性层,制备了器件结构不同的有机太阳能电池,分别考察了经多壁碳纳米管、山梨醇、溴掺杂处理后的PEDOT:PSS薄膜对器件光伏性能与稳定性能的影响。①多壁碳纳米管与山梨醇的掺杂,增加了器件中的漏电流,降低了器件的并联电阻,不利于器件效率的改善。溴掺杂对器件漏电流与并联电阻未有明显影响。②多壁碳纳米管、山梨醇、溴掺杂均可降低器件串联电阻,提高光电池能量转换效率。6wt%溴掺杂条件下,器件开路电压为0.60V,短路电流为10.31mA/cm2,FF为51.1,能量转换效率为3.16%,较未掺杂器件效率提高了约49%。8wt%山梨醇掺杂条件下,器件开路电压为0.53V,短路电流为11.27 mA/cm2,FF为49.1,能量转换效率为2.93%,较未掺杂器件效率提高了约38.2%。0.04wt%多壁碳纳米管掺杂条件下,器件开路电压为0.55V,短路电流为9.52 mA/cm2,FF为44.8,能量转换效率为2.35%,较未掺杂器件效率提高了约13%。③器件稳定性能实验显示：多壁碳纳米管(0.04wt%)与山梨醇(8wt%)掺杂对置于手套箱(高纯氩气；水、氧含量<1ppm；室温)中器件的稳定性能未有影响(20天)；相同实验环境中,溴(6wt%)掺杂则使器件效率在12天上开始下降。更多还原

【Abstract】 At present, the major disadvantage to organic solar cells is the low efficiency. How to improve its power conversion efficiency(PCE) has become crucial in its industrial development and competitiveness against traditional inorganic photovoltaics devices. In this paper, as anode decoration layer, the doping and modification of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film and its application in organic solar cells have been studied. The results are shown as follows:1. The PEDOT:PSS doped with multi-walled carbon nanotubes(MWCNTs), sorbital, and bromine transparent conducting thin films are fabricated separately on quartz substrates by blending-spin coating method. The effects of different dopants on the optical and electrical properties of PEDOT:PSS film have been investigated.①The optical transmission of PEDOT:PSS film in the wavelength region 550-850nm decreases after the addition of MWCNTs, while the sorbitol and bromine doping favor the improvement of PEDOT:PSS film optical transmittance②The electronic conductivity of PEDOT:PSS films doped with MWCNTs, sorbital, bromine are superior to that of the pristine PEDOT:PSS film. The conductivity of PEDOT:PSS film can be 400 times acvtive by doping of sorbitol (8wt%). The conductivity with bromine(6wt%) is appropriatly 300 times higher. The conductivity of MWCNTs (0.20wt%) doped PEDOT:PSS film is about 40 times higher than that of the non-doped film.2. The effects of the incorporation of three different types of dopants(MWCNTs, sorbitol and bromine) on corresponding changes in conductivity of PEDOT:PSS films have been studied and results was obtained by carrying out X-ray diffraction (XRD), scanning electron microscope (SEM), atom force microscope (AFM), X-ray photo-electron spectrum (XPS), etc.①The mechanism of conductivity enhancement in PEDOT:PSS film doped with MWCNTs mainly attribute to two effects:the "π-πinteraction" effect and the "net" effect. The former effect results fromπ-πinteractions between the thiophene rings of PEDOT backbone and MWCNTs when the individual nanotubes are dispersed in the PEDOT:PSS matrix at 0.04wt%, and at the same time the nanotubes are not contacting each other. The electronic density transfer occurs from PEDOT to MWCNTs in MWCNTNs-PEDOT:PSS help the charge more delocalized on the PEDOT chains. The latter stems from the formation of some conductive MWCNTs channels in the PEDOT:PSS matrix when the concentration of MWCNTs is 0.10wt%. These two effects can help charge transport and enhance the conductivity of composite films. Moreove, concentration of MWCNTs higher than 0.20wt% leads to a decrease in film conductivity resulting from the high contact resistance of MWCNTs each other.②The mechanism of conductivity enhancement in PEDOT:PSS film doped with sorbitol attributeds to the change of the resonant structure of PEDOT chain from a ’benzoid’ to a ’quinoid’structure, which represents a conformational change of the PEDOT chains from the coil structure into expanded-coil or linear structure. The more partially ordered structures in the expanded-coil or linear structure over the coil structure may yield additional benefits to the charge transfer leading to an improvement of the conductivity of PEDOT:PSS films.③The mechanism of conductivity enhancement in PEDOT:PSS film doped with bromine is affected by the oxidative characteristics of hydrobromic acid and bromine oxidation on PEDOT chains. Bromine reacts with water gives hydrobromic acid when bromine is added to PEDOT:PSS aqueous solutions, and there are some bromine molecules in Br2-saturated aqueous solutions. Hydrobromic acid and bromine molecules function as relatively weak oxidants and produce two effects on PEDOT chains. The first effect is necessary to achieve high hole carrier concentration by releasing more electrons from PEDOT chains which gave an increase in film conductivity cosequently, the other effect is because oxidantion of molecules damages the p-conjugation of PEDOT resulting in the loss of PEDOT:PSS film conductivity to some extent. The conductivity of PEDOT:PSS film is impoved once the former effect has a much greater impact on mechanism. Otherwise the conductivity of PEDOT:PSS film decreases.3. We also investigated the effects of MWCNTs, sorbitol and bromine doping on the photovoltaic performance and stability of polymer photovoltaic devices based on blends of poly(3-hexylthiophene) and [6,6]-phenyl-C61-buytyric acid methyl ester have been investigated separately.①The device performance is limited by lower shunt resistance due to the leakage current, the current gradually increased with increasing concentration of MWCNTs and sorbitol. However, the bromine doping of film can not affect the device leakage current and shunt resistance.②The efficiency of polymer PVs have been improved by reducing the device series resistance by doping PEDOT:PSS films with MWCNTs, sorbitol and bromine. For optimized bromine concentration(6wt%), the device exhibits pronounced improvement with ISC=11.27 mA/cm2, VOC=0.60V, and FF=51.1%. The corresponding PCE is 3.16%, which is higher about 49% than PCE of device with pure PEDOT:PSS film. The addition of the sobitol(8wt%) increased both the device short-circuit current(ISC=10.31 mA/cm2) and fill factor(FF=49.1%) resulting in an increase in efficiency by about 38.2% compared to the device with pure PEDOT:PSS film, although open-circuit voltage (VOC=0.53V)decreases a little after the addition of sobitol. With 0.4mg of MWCNTs(0.04wt%) added, the ISC and FF increase to 9.52 mA/cm2 and 44.8 respectively, while Voc remains nearly constant at 0.55V. And, thus, the PCE also increases to 2.35%, which is more about 13% than PCE of device without MWCNTs doping.③Solar stability experiments show that the stability of the device doped with MWCNTs(0.04wt%) and sorbitol(8wt%) are unchanged within 20 days at room temperature under high-purity argon atmosphere with less than 1 ppm oxygen and moisture in a glove box, while there is a decrease in the efficiency of the device doped with bromine(6wt%) after 12 days at the same experimental conditions.更多还原