Hole-transport materials based on benzodithiophene-thiazolothiazole-containing conjugated polymers for efficient perovskite solar cells

Conjugated polymers are promising hole-transport materials (HTMs) for designing efficient and stable perovskite solar cells (PSCs). The structure of polymer backbone and position of side substituents greatly influences their electronic properties, film morphology, and hence, the charge extraction and charge transport characteristics of HTMs. Herein, we design two novel donor-acceptor conjugated polymers based on benzodithiophene (BDT) bearing triisopropylsilyl substituents and thiophene-flanked thiazolothiazole block (Tz) with different side chain position. In polymer in-BDTTz alkyl chains are placed "toward" to the Tz moiety, while in aus-BDTTz "outward" to the Tz block. Polymeric HTM in-BDTTz enables 18.7% power conversion efficiency in devices outperforming that of PSCs with aus-BDTTz and reference devices employing poly(triarylamine) (PTAA). Furthermore, PSCs with in-BDTTz as HTM demonstrates stable operation comparable to that of PTAA-based devices. These findings feature alkylsilyl-substituted benzodithiophene-based polymers as promising dopant-free hole-transport mate-rials for efficient and stable perovskite photovoltaics.