Two novel high gap donor polymers – PBDTTSi-TzBI and PBDTTS-TzBI, based on imide-fused benzotriazole (TzBI) with asymmetric side chains and alkylsilyl (Si) or alkylthio (S) substituted 4,8-di(thien-2-yl)benzo-[1,2-b:4,5-b′]dithiophene (BDTT) – are successfully synthesized. The effect of the side chain variation on the photophysical, morphological and photovoltaic properties of blends of these polymers with fullerene and non-fullerene acceptors is investigated. The PBDTTSi-TzBI polymer shows a deeper highest occupied molecular orbital energy level, which results in higher open-circuit voltages. Nevertheless, the polymer solar cells fabricated using PBDTTS-TzBI in combination with PC71BM afford a higher power conversion efficiency of 7.3% (vs 4.0% for PBDTTSi-TzBI:PC71BM). By using the non-fullerene acceptor ITIC, the absorption of the blends extends to 850 nm and better device efficiencies are achieved, 6.9% and 9.6% for PBDTTSi-TzBI:ITIC and BDTTS-TzBI:ITIC, respectively. The better performance of the PBDTTS-TzBI:ITIC-based devices is attributed to the strong and broad absorption and balanced charge transport, and is among the best performances reported for non-fullerene solar cells based on TzBI-containing polymer donors.
Bibliographical noteFunding Information:
ZG and AN contributed equally to this work. The authors acknowledge financial support from Hasselt University ( BOF bilateral scientific cooperation ). WM, SA, ZG, BA and AN gratefully acknowledge financial support from the International Science Program (ISP), Uppsala University , Sweden. WM, NV, KV and JM thank the Research Foundation – Flanders ( FWO – Vlaanderen ) for continuous financial support (projects G.0B67.15 N, G.0D01.18 N and G.0B27.18 N).
© 2019 Elsevier B.V.
Copyright 2019 Elsevier B.V., All rights reserved.
- High gap polymers
- Non-fullerene solar cells
- Organic photovoltaics
- Side chain optimization