Unlocking high hole mobility in D-A-D hole transport materials via asymmetric donor engineering for perovskite solar cells

In perovskite solar cells (PSCs), the molecular architecture of hole-transport materials (HTMs) determines several key performance metrics, including interfacial energy alignment, optical response, and hole mobility. In this study, taking the promising HTM HiBT as a benchmark, we employed an asymmetric donor-engineering strategy to design a novel D ₁ -A-D ₂ small molecule ( HiBT-3 ). A systematic computational investigation combining density functional theory (DFT) and Marcus theory was carried out to evaluate its geometric and electronic structures, excited-state properties, and charge transport. The results show that the asymmetric donor engineering endows the new molecule with improved structural planarity relative to experimental HiBT, which is favorable for enhanced molecular stacking. Its frontier orbital levels align well with the valence-band edge of typical perovskites, ensuring efficient hole extraction. Notably, the theoretical hole mobility ( μ _h ) of HiBT-3 is significantly increased compared with the benchmark molecule, attributable to optimized transfer integrals. Furthermore, thermodynamic parameters suggest that HiBT-3 exhibits improved structural stability. Consequently, HiBT-3 emerges as a promising candidate for high-efficiency PSCs, validating asymmetric donor substitution as an effective strategy for HTM design.