Effect of aggregation behavior on photovoltaic performances in benzodithiophene-thiazolothiazole-based wide band-gap conjugated polymers with side chain position changes
Two conjugated donor polymers (PBTz-1 and PBTz-2) based on benzo[1,2-b:4,5-b']dithiophene and thiazolothiazole (TzTz) with different side chains (2-hexyldocyl) positions were designed and synthesized. Both polymers had the similar optical and electrochemical bandgaps as well as deep HOMO levels, but significantly different aggregation behaviors in solutions and photovoltaic performances in NF PSCs. In combination with the absorption spectra, atomic force microscopy and X-ray diffraction measurements, we found that PBTz-1 exhibited stronger aggregation in solution and crystallization in film than that of PBTz-2. When they were blended with non-fullerene acceptor (IT-4F), their blend films show big difference in organizations and morphologies. In PSCs, the power conversion efficiency (PCE) of PBTz-1:IT-4F-based PSC was only 6.2%, while the PCE of PBTz-2:IT-4F-based PSC was up to 12.4%.