Preparation And Photovaltaic Properties Of Electon Acceptors With Fluorene And1,1-Dicyanomethylene-3-Indanone Groups

As a promising environment-friendly and renewable energy conversion technology,polymer solar cells?PSCs?have attracted extensive attention.Considerable attention has been paid in non-fullerene?NF?acceptors for PSCs due to their advantages,such as good light absorption and the highly tunable properties by chemical modifications and potential for low-cost synthesis.Non-fullerene?NF?acceptors can be arbitrarily divided into three constituting components:the conjugated backbone,the side chains,and the substituents,and the photovoltaic properties are determined by the three aspects.So far,the influence of side chain and molecular configuration on polymer donors in polymer:fullerene blends has been studyed widely,while little is known about the influence of them on the performance of non-fullerene acceptors in polymer:non-fullerene acceptor blend PSCs.Based on an easily accessible conjugated backbone of dicyanomethylene indanone-thiophene-fluorene-thiophene-dicyanometnylene indanone?DICTF?,the bland of PTB7-Th:DICTF exhibited a high PCE of 7.93%,which is comparable to that of the device based on PTB7-Th:PC₇₁BM.We selected DICTF as the structural platform for non-fullerene molecular acceptors,two non-fullerene molecule acceptor materials were synthesized with different said chain and molecular configuration.We explored the influence of side chain and molecule configuration on the performance of non-fullerene acceptors in polymer:non-fullerene acceptor blends PSCs.The main contents are as follows.?1?By replacing the alkyl side chains with the TEGs,two non-fullerene molecule acceptor materials?DICTF-C10 and DICTF-TEG?were synthesized with the same conjugated backbone to that of DICTF.The effect of the two types of side chains on the photovoltaic properties of the two non-fullerene acceptors was disclosed.It was found that replacing decyl chains with TEG chains can improve the?-?stacking interaction of conjugated backbones of the acceptors in solid state as expected,while also led to unfavorable film morphology of the active blends and deteriorated device performance,which is completely different from reported results that introducing TEG chains into conjugated polymer donors can improve device performance with optimized molecular packing in polymer:fullerene blends.This comparative study demonstrates that empirical side chain engineering by the introduction of OEG chains into conjugated backbones does not always straightly translate into performance enhancement in resulted BHJ devices.?2?A non-fullerene molecule acceptor?V-DICTF-C10?with a V shape of conjugated backbone was synthesized to further explore the influence of different conjugated backbone configuration on the photoelectric properties of non-fullerene organic solar cells.The small molecule DICTF-C10 is linear configuration,while V-DICTF-C10 is V configuration.By comparing the optical properties,the electrochemical properties and the photovoltaic performance of the two small molecule acceptors,we found that changes in the conjugated backbone configuration have a great influence on the molecular morphology and the molecular stacking of non-fullerene acceptors.The optimized BHJ films give a more unfavourable molecular morphology for PTB7-Th:V-DICTF-C10,the blend film of PTB7-Th:V-DICTF-C10 exhibited lower and more unbalanced hole and electron mobility.Unfavourable molecular and morphology resulting in the lower J_sc and FF in the PTB7-Th:V-DICTF-C10 device.Finally,the PTB7-Th:V-DICTF-C10 devices displayed a maximum PCE of only 2.19%.