The optimization of π-bridge for trialkylsilyl substituted D-π-A photovoltaic polymers. (October 2021) - Du, Mengzhen
Abstract: Polymers with donor-π-acceptor (D-π-A) structure are widely used in organic solar cells (OSCs) because of their tunable optoelectronic properties. With the distinct 2D-conjugated structure and the s*(Si)–p*(C) bond interaction of the trialkylsilyl substitution, the electron-donating unit of 4, 8-bis(5-(tripropylsilyl)thiophen-2-yl)benzo[1, 2-b:4, 5-b']dithiophenes (BDTT-Si) shows large potential to construct promising photovoltaic polymers. However, the studies of π-bridge in BDTT-Si-based polymers are not sufficient, and structure-properties relationship is still unclear. Here, we designed and synthesized three polymers PE7a, PE7b and PE7c, with BDTT-Si and difluorinated benzo[d] [1, 2, 3]triazole (BTA ) as the D unit and A unit, respectively. By using thieno[3, 2-b]thiophene (TT ), TT with hexyl (C 6 -TT ) and TT with undecyl (C 11 -TT ) as the π-bridge, the solubility, crystallinity and optoelectronic properties of three polymers can be fine-tuned. When blended with the non-fullerene acceptor Y6, PE7a-c show different photovoltaic performance. The polymer PE7c realized the highest power conversion efficiency (PCE) of 11.4%, obviously higher than that (9.5%) of J71 with thiophene as π-bridge. The results indicate that the introduction of TT π-bridge with suitable alkyl chain into BDTT-Si containing polymer is an effective strategy to improve the photovoltaic performance. Graphical abstract: Image 1 Highlights: Three D-π-A type conjugated polymers PE7a, PE7b and PE7c were synthesized as donor materials in OSCs. The molecular solubility and morphology of blend films can be regulated by alkyl chains optimization on the TT π-bridge. The PCE of PE7c-based photovoltaic device reached 11.4% when blended with the non-fullerene acceptor Y6.