Backbone Conformation Tuning of Carboxylate-Functionalized Wide Band Gap Polymers for Efficient Non-Fullerene Organic Solar Cells

Abstract

Two carboxylate-functionalized wide band gap polymers, 2TC-TT-BDTFT and 2T-TTC-BDTFT, which feature a fluorinated benzodithiophene (BDTFT)-alt-2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene (2T-TT) backbone having different carboxylate attaching positions, were designed and synthesized. By variation of the substitution position of carboxylate groups on the 2T-TT unit, the backbone conformation of the designed building blocks 2TC-TT and 2T-TTC and their corresponding donor–acceptor polymers was fine-tuned as demonstrated by single crystal study and DFT calculation, thus yielding a large device performance difference in organic solar cells. As a result of the relatively higher planarity of the 2T-TTC unit in which the two carboxylate groups were attached on the inner thieno[3,2-b]thiophene moiety, the 2T-TTC-BDTFT polymer exhibited a red-shifted UV–vis absorption, stronger aggregation, and improved charge transport property than its polymer analogue 2TC-TT-BDTFT, in which the two outer thiophene rings were fun...