Interfacial Modification Of Water/Alcohol-Soluble Fluorene-Based Conjugated Electrolytes In The Organic Photovoltaics

In recent years, organic solar cells(OSCs) have drawn considerable attention for their advantages over their inorganic counterparts, such as low materials costs, light weight, simple preparation and flexibility. During the past decade, the power conversion efficiency(PCE) of single-junction OSCs has been exceeded 10%, gradually achieving the threshold of commercialization,which can not only be ascribed to the development of excellent light-harvest materials and the employment of highefficiency and stable device structure, but also the incorporation of interfacial modification materials between active layer and electrode. Interfacial modification plays a vital role in achieving high-performance OSCs devices by improving the compatibility between activelayer and eletrode and tuning the work function of electrode by introducing interfacial dipoles, which can facilitate the charge extraction and collection. In the dissertation, we incorporated different types of conjugated electrolytes as cathode interfacial materials in the OSCs, exploring the intrinsic mechanism of interfacial layer on the device performance.We synthesized two fluorene-based liquid-crystal conjugated polyelectrolytes(LCCPEs) PF6 Ncbp and PF6 lmicbp combined with different polar groups on the side chains to apply on the surface of ZnO to form ZnO/LCCPEs bilayer as electron transporting layers(ETL) in the inverted device. Combined with PFN, which is analogous to PF6 Ncbp but without mesogenic groups on the side chains, we find that liquid-crystal groups possess the ability of spontaneous orientation, which can induce a re-arrangement of dipole moments at the interface of ZnO, subsequently lowering energy barrier of electron transporting. In addition,LCCPEs not only favor intimate interfacial contact between inorganic layer and organic layer, but also induce activelayer to form the nanofibers morphology which is in favor of the enhancement of charge transportation and collection.We also designed three water/alcohol small conjugated electrolytes(SMCEs) 2T-(FN-Br)2,3T-(FN-Br)2 and 4T-(FNBr)2, which have the same ammonium salt polar groups but different conjugated skeleton, to explore the relevance between the π-conjugated skeleton of SMCEs and the device performance. We find that the increasing of conjugated length help to form more intimate contact, more uniform morphology of activelayer and higher electron mobility. When 4T-(FNBr)2 with the largest π-conjugation skeleton is applied as interfacial layer, devices based on PTB7:PC70BM as active layer stystem can achieve a high power conversion efficiency of 8.40%. The results provide a new avenue to develop novel interfacial materials in the future.