Minimizing interfacial energy losses via fluorination strategy toward high-performance air-fabricated perovskite solar cells

Sub-bandgap state-induced radiative recombination and trap-assisted nonradiative recombination at the interface between the perovskite layer and hole transport layer in n-i-p perovskite solar cells (PSCs) significantly limit further improvements in power conversion efficiency (PCE) and stability. In this work, we introduce a simple yet effective fluorination strategy to mitigate these recombination losses by simultaneously achieving defect passivation, tensile strain release, and modulation of interfacial energy band alignment. The incorporation of fluorine (F) groups not only enhances defect passivation through strong chemical bonding but also improves the moisture resistance of perovskite films and devices. We reveal the critical influence of the number and position of F groups on the benzene ring in determining device photovoltaic performance. PSCs modified with 3,5-difluoro-benzamidine hydrochloride (3,5-DFBH) demonstrate a remarkable PCE of 24.57 %, coupled with enhanced long-term stability. These PSCs, among the highest-performing devices fabricated in ambient air, maintained over 90 % of their initial power conversion efficiency (PCE) after 2700 h of storage at 10 % to 20 % relative humidity, and withstood 1700 h of exposure to heat at 65 °C. This work provides a viable pathway to simultaneously improve both the photovoltaic performance and stability of PSCs by mitigating sub-bandgap and trap-assisted recombination through fluorination.