Design of multifunctional phosphonic acid molecule for highly efficient and stable inverted perovskite solar cells
Inverted perovskite solar cells (PSCs) suffer from defect-mediated nonradiative recombination and inefficient charge extraction, particularly at the buried interface and grain boundaries (GBs), which limit power conversion efficiency (PCE) and operational stability. This study introduces a multifunctional phosphonic acid molecule, (2-(3,6-bis(trifluoromethoxy)-9H-carbazol-9-yl)ethyl)phosphonic acid (M28), as an additive in the perovskite precursor solution. M28 spontaneously segregates toward the buried interface and GBs, fulfilling three roles: (1) slowing crystallization to enlarge grains and improve film quality, (2) passivating defects to suppress charge recombination, and (3) inducing p-type doping to create an extra electric field that promotes hole transport. Devices incorporating M28 achieve a champion PCE of 25.96% and retain 80% of initial efficiency after 1500 h of maximum power point tracking. This work demonstrates the efficacy of multifunctional phosphonic acid additives in addressing buried-interface and GB defects, offering a viable route to high-performance, stable inverted PSCs.