Triarylamine-Modified Phenothiazine Small Molecules as Hole-Transporting Materials in Wide-Band-Gap Perovskite Solar...

Perovskite solar cells (PSCs) offer exceptional tunability of optoelectronic properties, enabling wide-band-gap absorbers that are highly attractive for semitransparent devices in building-integrated photovoltaics (BIPV). However, challenges associated with stability, scalability, and materials' cost continue to limit their practical deployment, highlighting the pivotal role of hole transport materials (HTMs) in achieving high efficiency and durable device operation. Herein, we report the rational design and synthesis of three novel small-molecule HTMs based on phenothiazine-triarylamine cores, prepared via concise synthetic routes with moderate-to-high yields. The electron-rich, nonplanar phenothiazine scaffold enables suppressed aggregation and favorable energy-level alignment, rendering these materials particularly suitable for wide-band-gap and semitransparent PSCs. When implemented in FAPbBr₃-based semitransparent devices, two candidates (SM1 and SM2) achieve power conversion efficiencies comparable to those of the state-of-the-art poly(triarylamine) (PTAA) (PCE = 6.26% and 6.09% for SM1 and SM2, respectively, vs 6.39% for PTAA). Notably, their enhanced optical transparency leads to comparable light-utilization efficiency (LUE) (4.05 and 3.99 for SM1 and SM2, respectively, vs 4.07 for PTAA), with outstanding and superior bifaciality factors (84% and 82% for SM1 and SM2, respectively, vs 81% for PTAA), providing a distinct advantage beyond conventional opaque-PV efficiency metrics. These findings position phenothiazine-based HTMs as promising, cost-effective alternatives to PTAA for scalable semitransparent perovskite solar cells.