Unveiling the Role of Solvent‐Hole Transport Layer Interactions in the Performance of Perovskite Solar Cells

Rational screening of solvents that improve wettability without compromising the integrity of organic hole transport layers (HTLs) remains challenging, primarily because of limited understanding of solvent‐HTL interactions. Here, poly [bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) is employed as a model system to systematically explore how solvent‐PTAA interactions govern HTL wettability and the microstructure of metal halide perovskite (HP) films. Solvents with a dielectric constant ( ε r ) > 15 are poor solvents, while their interactions with PTAA critically determine its wettability and the quality of HP films. Alcohols form weak n → π * interactions with PTAA, yielding only marginal improvements. In contrast, the widely used N, N‐Dimethylformamide (DMF) induces strong n → π * interactions that fracture the PTAA layer, leading to a defective interface. Remarkably, acetone provides an optimal interaction strength between carbonyl groups (C = O) of the solvent and the aromatic rings of PTAA, which enhances wettability while preserving HTL integrity by forming a polarity‐compatible interface with the HP precursor solution. This universal enhancement in quality of both three‐dimensional (3D) and low‐dimensional (LD) HPs boosts the power conversion efficiencies (PCEs) of corresponding solar cells (SCs) to 22.85% and 17.45% with increases of ∼12% and ∼25%, respectively, over DMF‐treated counterparts. This work offers a molecular‐level insight into solvent‐HTL interactions for advancing HPSCs.