Performance And Photophysical Study Of High Efficiency Non-fullerene Solar Cells

With the rapid development of non-fullerene acceptors,the performance of nonfullerene organic solar cells was becoming more and more high,and the efficient nonfullerene system has become an important part of organic solar cells.To further improve the performance of non-fullerene organic solar cells,it was crucial to understand their charge carrier dynamics,as followed:Firstly,we compared the PBDB-TF:IT-M non-fullerene and PBDB-TF:PC71BM fullerene device function and the ultrafast photophysical properties,and how they were affected different film structures,device function and the ultrafast photophysical process induced by using a popular solvent additive 1,8-diiodooctane(DIO).We showed that ultrafast charged generation occurs in both of the material systems while efficient hole transfer for the IT-M blend only exists in the film with optimal morphology.For PBDBTF:IT-M blend film,the significantly increased charge density was observed in DIO processed film,while there was little change for the PC71 BM blend film indicating that geminate recombination was a significant loss channel in nonfullerene acceptor-based blends limiting device performance.Secondly,the effects of DIO and 1-chloronaphthalene(CN)additives on device function and the related ultrafast photophysical process were studied.It was found that both the DIO and CN can lead to an enhanced structural order in in-plane direction and increased average lifetime of excitons in neat PBDB-TF films.The blend samples prepared with both additives show increased initial exciton yields,in blend samples prepared with DIO,the formation of polymer triplet excitons through bimolecular charge recombination could be effectively suppressed compared with the pristine and CN-processed samples.The DIO-processed device was also found to have the superior fill factor due to suppressed charge carrier recombination.In summary,our findings have revealed the relationships between PBDBTF:IT-4F morphologies induced by different additives and photophysical processes as well as their effects on the photovoltaic conversion.