Polymer Solar Cells

Harnessing sustainable and clean solar energy is one of the most effective way to alleviate the energy crisis and environmental contamination.Among them,photoelectric conversion is an important means of solar energy utilization.In recent years,organic solar cells have been extensively researched due to their flexibility,light weight,ease of processing,and adjustability.Many materials have been investigated for the preparation of high-performance organic solar cells.Among them,polymer materials play a very important role in both fullerene and non-fullerene solar cells.In this project,we focus on the molecular design of polymer acceptor materials and the optimization of spin coating processes for active layers of devices.First,we systematically investigated the effect of halogenation strategy of polymer acceptors on photovoltaic performance.We copolymerized the electron-deficient unit BNIDT embedded with the B?N bond with three electron-rich units which are benzodithiophene(BDT),fluorinated BDT,and chlorinated BDT named BN-BDT,BN-BDT-F and BN-BDT-Cl.Then,using PBDB-T as the donor,an all-polymer solar cells(all-PSC)were prepared.The efficiencies of all-PSCs were significantly promoted from nonhalogenated BN-BDT(1.60%)to fluorinated BN-BDT-F(3.71%)and further elevated to chlorinated BN-BDT-Cl(4.23%).Device characteristics show that the photovoltaic performance of non-halogenated polymer acceptors can be significantly improved by fluorination and further improved by chlorination.This is the first comprehensive study to compare the performance of non-halogenated,fluorinated and chlorinated compounds in polymer acceptors.In order to further improve the efficiency of such polymer acceptors,we developed two new conjugated polymers named BN-T and BN-2fT by copolymerizing BNIDT with thiophene and 3,4-difluorothiophene,respectively.The results show that these polymers have a wide absorption spectrum covering 350-800 nm,low energy levels,and bipolar thin film-transistor characteristics.We also prepared all-polymer solar cells with PBDB-T as the donor and BN-T/BN-2fT as the acceptor.The champion device with BN-2fT as the acceptor afforded a PCE of 8.78% and a fill factor of 70.4%.This set a new record for the efficiencies of polymer acceptors containing B?N bonds and provided new ideas for the development of new highly efficient polymer acceptors.Finally,considering the importance of the active layer spin-coating process to device performance,we systematically studied the application of a typical wide band gap donor polymer,PBDT-PhI,in non-fullerene solar cells.After fully screening of the acceptors,the performance of the PBDT-PhI/ITCT system was found the best.Furthermore,the active layer morphologies of the devices were fine-tuned by selecting different spin coating solvents.Finally,the CB/CF mixed solvent strategy was used to effectively increase the charge dissociation rate of the active layer and reduce the composite loss.Because of this method,significantly improved photoelectric conversion efficiency(PCE)of 10.17% based on the PBDT-PhI/ITCT system has been achieved.