Multifunctional phosphonic acid additive enables efficient and stable inverted perovskite solar cells

Achieving efficient defect passivation is crucial for enhancing both the performance and stability of perovskite solar cells (PSCs). In this study, we demonstrate that incorporating [4-(3,6-dibromo-9H-carbazol-9-yl)butyl]phosphonic acid (Br-4PACz) as a multifunctional additive into inverted PSCs significantly improves device metrics. The phosphonic acid group in Br-4PACz effectively passivates undercoordinated Pb2+ ions, thereby reducing defects and improving perovskite film quality. Furthermore, Br-4PACz optimizes energy level alignment, promoting efficient charge extraction and suppressing non-radiative recombination. As a result, the Br-4PACz-modified inverted MAPbI3 device exhibits a remarkable increase in Voc from 1.00 V to 1.10 V and in power conversion efficiency from 16.9% to 19.3%, along with enhanced moisture stability. This work underscores phosphonic acid-based molecular engineering as a promising approach for developing high-performance stable inverted PSCs.