Achieving efficient polymer solar cells based on benzodithiophene–thiazole-containing wide band gap polymer donors by changing the linkage patterns of two thiazoles

Abstract

The combination of building blocks is very important when controlling molecular device performance. To study this issue, in this work, we designed and synthesized two wide band gap polymers (PBTz and PTzTz), which are composed of 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophen and different combinations of two thiazoles, bithiazole (BTz) and thiazolothiazole (TzTz). Both polymers showed good thermal stabilities and good solubilities in chlorinated organic solvents. PTzTz exhibited a wider absorption spectrum and a redshifted maximum absorption wavelength compared to PBTz, while PTzTz showed a higher highest occupied molecular orbital (HOMO) level of −5.42 eV compared to PBTz (−5.44 eV). When a non-fullerene (NF) electron acceptor (IT-4F) was used as the electron acceptor to fabricate polymer solar cells, the PBTz:IT-4F-based device showed a power conversion efficiency (PCE) of 8.76%, while the PTzTz:IT-4F-based device showed a better PCE of 10.63%. BHJ morphology analysis confirmed that the PTzTz:IT-4F blend film had better phase-separation and charge transport compared to the PBTz:IT-4F blend film. This work implies that the TzTz unit is a better unit to make polymer donors for NF PSCs.