Self-assembled hole-transport material incorporating biphosphonic acid for dual-defect passivation in NiO_x-based perovskite solar cells

The efficiency and stability of nickel oxide (NiO_x)-based perovskite solar cells (PSCs) are critically hindered by defects and suboptimal charge transfer at the interface between perovskite crystals and the NiO_x layer. In this study, we introduce a self-assembled hole transport material, D-3PACz, featuring bisphosphonic acid anchoring groups, to address these challenges. D-3PACz is proved to be effective in improving the surface properties of nickel oxide, optimizing the energy level alignment and enhancing hole extraction capability. Meanwhile, the robust interaction between phosphonic acid and the perovskite layer enables D-3PACz to effectively direct the growth of perovskite crystals. These findings result in devices exhibiting reduced non-radiative recombination losses, lower defect-state densities, and enhanced hole extraction performance, culminating in a comprehensive improvement in device parameters. Excitingly, the D-3PACz based devices obtain a champion PCE of 23.8% with elevated stability. Our work presents the superiority of the proposed D-3PACz material for efficient and stable PSCs.