Design,synthesis And Properties Of Nonfused Acceptors Based On Thieno[3,2-b]thiophene

In the last few years,with the development of fused ring electron acceptors(FREAs)and the optimization of devices and morphology,the power conversion efficiency(PCE)of the best organic solar cell(OSC)has exceeded 20%.However,the relatively high synthesis difficulty and low yield lead to the high production cost of FREAs,which is adverse to their commercial application.In contrast,nonfused ring electron acceptors(NFREAs)with simple structure,easy synthesis,high yield,low cost and high stability have promising potential for commercialization.In this thesis,a series of nonfused acceptor materials based on thiopheno[2,3-b]thiophene were designed and synthesized,and the influence of molecular structure on photoelectric properties,molecular conformation,stacking mode and photovoltaic performance was systematically explored.The following is a summary of the research content of each chapter:Firstly,two NFREAs 2T2TT-F and 2T2 Se T-F with thiopheno[3,2-b]thiophene(TT)and selenopheno[3,2-b]thiophene(Se T)as π bridge units were designed and synthesized.Two NFREAs show similar absorption spectra in the film,but 2T2TT-F possesses a higher-lying lowest unoccupied molecular orbital(LUMO)energy level than 2T2 Se T-F.In addition,theoretical calculations show that 2T2 Se T-F exhibits a more planar molecular geometry,which is beneficial for stronger intermolecular interaction and higher crystallinity.However,morphological studies showed that PM6:2T2TT-F blends showed more favorable phase separation due to their proper compatibility,which could effectively inhibit charge recombination and obtain higher exciton dissociation efficiency and carrier mobility.Therefore,the devices based on2T2TT-F obtained a higher PCE(11.31%)than those based on 2T2 Se T-F(8.47%).Secondly,two isomeric NFREAs of 2T2STT-F and 2T2TTS-F were designed and synthesized based on 2T2TT-F,in which two alkylthio side chains were pended into the6-position of two thieno[3,2-b]thiophene(TT)units closer to the core for 2T2STT-F and the 3-position of TT closer to the end group for 2T2TTS-F,respectively.The influence of pending positions on photophysical and photovoltaic properties were studied.Compared with 2T2TTS-F,2T2STT-F possesses redshifted absorption,stronger intermolecular packing and higher molecular crystallinity,and forms large aggregates when blending with polymer PM6,leading to an inferior power conversion efficiency(PCE)of 1.31%.PM6:2T2TTS-F based devices exhibit a higher PCE of8.81%,which is mainly attributed to the appropriate morphology with more suitable phase separation and fibril network of the PM6:2T2TTS-F blend,less charge carrier recombination and efficient charge transport.