Donor-Side-Dependent Electronic Regulation in D1−π–D2 Hole Transport Molecules: Balancing Energy Alignment and Interfacial Charge Transfer in Perovskite Solar Cells

Designing hole-transport materials (HTMs) with excellent stability, outstanding carrier mobility, and favorable interface properties is crucial for advancing perovskite solar cells (PSCs) toward large-scale commercialization. In this work, based on the experimental molecules DTPA and DPTPA, four derivative molecules (DPTPA-1, DPTPA-2, DN-1, and DN-2) were designed by incorporating electron-withdrawing thiophene and pyrrole groups into the π-bridge. We systematically investigated which placement of the electron-withdrawing group, closer to the stronger donor of two triphenylamines (T-TPA) or the weaker donor of diphenylamine (DPA), could more effectively enhance performance. Our results show that DPTPA-2, which introduces thiophene on the weaker donor (DPA) side, and DN-2, which incorporates pyrrole groups, significantly enhance molecular planarity, optimize the HOMO energy level, and improve hole mobility and solubility compared to DTPA and DPTPA. Furthermore, these DPA-side modified molecules exhibit higher adsorption energies and more stable interfaces with the perovskite layer. Although DPTPA-1 and DN-1 modified with T-TPA exhibit slightly lower mobility and adsorption energy, they still achieve the highest charge-transfer amount into the perovskite. Overall, introducing thiophene and pyrrole groups at the DPA end can effectively enhance molecular mobility and adsorption energy to perovskite, while incorporating thiophene and pyrrole groups at the T-TPA end increases the charge transfer amount of HTMs into the perovskite material.