Heptacyclic Ladder-Type Triarylamine-Functionalized Polymers as Hole-Transporting Layers with Stirring-Controlled Aggregation for Efficient and Stable Tin Perovskite Solar Cells

Tin-based perovskite solar cells (TPSCs) are promising lead-free photovoltaics but remain limited by inefficient hole extraction, interfacial recombination, and poor operational stability. Here, we report a series of benzodipyrrole (BDP)-based conjugated polymer hole-transporting layers (HTLs) with controlled aggregation for inverted TPSCs. By integrating triarylamine-like aryl substitution into a rigid, coplanar BDP ladder backbone, a polymeric PBDP-Ph HTL with favorable energy-level alignment, high hole mobility, and improved interfacial compatibility was synthesized. Beyond molecular design, we identify stirring time of the polymer precursor solution as a critical parameter governing solution-state aggregation, film morphology, and device performance. An optimal stirring duration of 10 min yields well-dispersed polymer chains, smooth HTL films, and high-quality perovskite crystallization, thereby suppressing nonradiative recombination and enhancing charge extraction. Consequently, TPSC employing PBDP-Ph fabricated via a two-step approach delivers a power conversion efficiency of 9.1%, outperforming conventional PEDOT:PSS-based and other BDP-derived devices, while exhibiting markedly improved long-term and operational stability.