A thieno[3,4-b]thiophene-based small-molecule donor with a π-extended dithienobenzodithiophene core for efficient solution-processed organic solar cells

Abstract

A small molecule donor STB-4 with dithieno[2,3-d′:2′,3′-d′]benzo[1,2-b:4′,5′-b′]dithiophene (DTBDT) as the central moiety was designed and synthesized for solution-processed bulk-heterojunction solar cells. An optimized power conversion efficiency of 8.17% with an open-circuit voltage of 0.904 V, a short-circuit current of 13.33 mA cm⁻², and a fill factor FF of 0.67 was achieved after solvent annealing (SVA). According to the detailed morphology investigations, we found that SVA refined the phase-separated morphologies of the blends, allowing the domains to become well defined with anappropriate size that is beneficial for device performance.