聚合物反向电池的相分离机制和光伏性能研究

Organic polymer solar cells (PSCs) based on the bulk heterojunction structure have made great progress and the power conversion efficiency (PCE) of this PSCs device have reached over 10% in the recent days. However, the conventional structure has drawbacks in the stability and lifetime of device, so the efficiency and stability still need to be improved to fulfill the commercial requirements. .Inverted organic solar cells, which take coated ITO as cathode and a high work function (HWF) metal as anode, can improve the drawbacks in the stability and oxidizability when exposed in oxygen and moisture. In addition, it has been reported that the charge collections are also enhanced in the inverted geometry, owing to inherent vertical phase separation with a donor-enriched top surface and an acceptor enriched bottom surface in the active polymer of inverted solar cells device. Hence, inverted geometry contains the advantages of device stability, design flexibility and higher PCE. So far there still are some controversies because of the insufficient research of vertical phase separation related donor/acceptor phase..This project develops a model system of inverted structural PSCs device to research the mechanism and photovoltaic properties of the inverted phase separation, and to investigate impact factor of different modification layer of cathode such as preparation process, morphology and work function. The goals are to choose suitable polymer as donor materials and fullerene derivatives as acceptor materials, to investigate the mechanism of microphase separation，charge mobility and collection. All those investigation being done to achieve a high efficient performance and stability of PSCs device and then offer theoretical basis and experimental parameter for inverted organic polymer solar cells.

聚合物本体异质结光伏电池目前已经取得了巨大的进展，光电转换效率超过10％，即将进入产业化阶段，但是其稳定性和效率仍需提升。反向光伏电池采用涂有修饰层的ITO作为阴极、高功函数的金属作为阳极，解决了传统正向电池的稳定性和耐水、氧等问题；此外，在反向光伏电池的光活化层中存在着给体和受体材料的垂直相分离，能够有效地改善传统电池内部电子和空穴的传输和收集特性，有望获得高稳定性和高光电转换效率的聚合物光伏器件。然而迄今，关于反向电池中的给/受体垂直相分离研究的尚不充分，且有一定的分歧。.本项目拟研究聚合物反向电池中的垂直相分离机制和光伏特性；探索各种阴极修饰层的制备、形貌和功函数；选择合适的聚合物给体和富勒烯受体，通过各种退火方式制备反向电池器件；系统研究光活化层在电极上的相分离机制、微结构以及电子传输和收集规律，获得一种高效、稳定的聚合物光伏电池，为有机聚合物反型器件的发展提供理论依据和实验参数。

反向光伏电池采用涂有修饰层的ITO作为阴极、高功函数的金属作为阳极，解决了传统正向电池的稳定性和耐水、氧等问题；此外，反向电池活性层中存在给/受体材料的垂直相分离，能够有效地改善传统电池内部电子和空穴的传输和收集特性,获得高稳定性和高光电转换效率。通过四年研究，本项目取得了一系列有价值的创新性成果，主要包括以下4个方面：. （1）系统考察了ITO导电层的透过率与活性层中聚合物吸收光谱的关系。选择窄带隙、中等带隙以及宽带隙三种聚合物作为研究对象，发现对于窄带隙的聚合物采用方块电阻为13.2Ω/□的ITO性能最佳；而针对宽带隙和中等带隙聚合物，选择透过率更高的14.7Ω/□ITO性能更佳，为反向电池研究奠定了基础；. （2）制备了四种基于茚并芴的水/醇溶性阴极界面修饰层（PIFNB、PIFN、PIFNB-Et、PIFNO），与经典的PFN相比具有更佳的表面功函，其中以PIFNB作为阴极界面层，以PTB7和PC71BM为活性层的光伏器件光电转化效率为8.52%，比经典的PFN界面器件提高了6.5%。此外考察了PIFN、PIFNB-Et、PIFNO界面对PTB7:PC71BM反向器件的性能与垂直相分离之间的关系。. （3）系统研究了四氢呋喃蒸汽退火对二噻吩并苯-苯并噻二唑类聚合物（P3）正向和反向光伏器件性能的影响，发现与正向电池8.37%的效率相比，反向电池的效率减低了6.56%，出现了反常现象。其主要原因是，活性层垂直相中聚合物随着溶剂熏蒸向活性层底部迁移。由于聚合物在活性层中传输的是空穴，聚合物在薄膜底部的富集有利于空穴传输，从而导致正向电池性能提升而反向电池性能下降。. （4）制备了11种基于氟代喹喔啉和氟代苯并噻二唑的新型聚合物，有效的拉深了聚合物的HOMO能级，实现了器件开路电压和转换效率的同步提升。其中含有氟代喹喔啉的聚合物-PBDTT-DFTQ光电转换效率达7.76%；含有氟代苯并噻二唑的聚合物-P3 转化效率为8.47%，是该类材料正向电池的最高效率之一。. 此外，将非富勒烯受体(ITIC)掺入P3:PC71BM活性层中，拓宽了活性层的光谱响应范围，有效提升了短路电流密度，光电转换效率达到9.75%。