Locking Surface Dimensionality for Endurable Interface in Perovskite Photovoltaics

ABSTRACT Surface passivation with organic ammoniums improves perovskite solar cell performance by forming 2D/quasi‐2D structures or adsorbing onto surfaces. However, complexity from mixed phases can trigger phase transitions, compromising stability. The control of surface dimensionality after organic ammonium passivation presents significant importance to device stability. In this study, we developed a poly‐fluorination strategy for surface treatment in perovskite solar cells, which enabled a high and durable interfacial phase purity after surface passivation. The locked surface dimensionality of perovskite was achieved through robust interaction between the poly‐fluorinated ammoniums and the perovskite surface, along with the steric hindrance imparted by fluorine atoms, reducing its reactivity and penetration capabilities. The high hydrophobicity of the poly‐fluorinated surface also aids in moisture resistance of the perovskite layer. The champion device achieved a power conversion efficiency (PCE) of 25.2% with certified 24.6%, with 90% of its initial PCE retained after approximately 1200 h under continuous 1‐sun illumination, and over 14,400 h storage stability and superior stability under high‐temperature operation.