Comparative study on the effects of alkylsilyl and alkylthio side chains on the performance of fullerene and non-fullerene polymer solar cells

Authors：Genene, Zewdneh; Negash, Asfaw^*; Abdulahi, Birhan A.; Eachambadi, Raghavendran Thiruvallur; Liu, Zhen; Van den Brande, Niko; D'Haen, Jan; Wang, Ergang; Vandewal, Koen; Maes, Wouter^*; Manca, Jean; Mammo, Wendimagegn; Admassie, Shimelis

Source：Organic Electronics: physics, materials, applications , 2020, 77: 105572.

DOI：10.1016/j.orgel.2019.105572

• High gap polymers
• Organic photovoltaics
• Side chain optimization
• Alkylthio
• Alkylsilyl
• Non-fullerene solar cells

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 (5) 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.

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