Multifunctional fluorinated ammonium salt for high-performance all-inorganic CsPbI2Br perovskite solar cells with efficiency of 16.29%

Abstract

All-inorganic CsPbI2Br material has attracted considerable attention due to its good balance between phase stability and absorption capacity. However, the power conversion efficiency (PCE) and device stability of CsPbI2Br-based perovskite solar cells (PSCs) still lag far behind those of their counterparts, mainly deriving from the notoriously poor moisture stability under humid environment and large serious charge recombination. Herein, a typical phenethylammonium chlorine (PEACl) and its fluorinated derivative 4-fluoro-phenethylammonium chlorine (F-PEACl) are individually incorporated to modify the surface of CsPbI2Br film to ameliorate the above issues. Benefiting from the comprehensive passivation effect of ammonium halogen, the trap states of treated CsPbI2Br are vastly suppressed. In particular, fluorination significantly increased the dipole moment and hydrophobic property of F-PEACl. Thus, the present CsPbI2Br PSC achieves a champion PCE of 16.29% with high open-circuit voltage of 1.272 V, while the reference device and PEACl-treated device yield PCEs of 14.30% and 15.64%, respectively. More importantly, the PSC with F-PEACl capping layer retains 87.2% of its initial PCE after 1000 h storage under 20% RH ambient without encapsulation. Our results reveal the underlying mechanism of performance improvement by surface passivation strategy and provide an effective approach to further boost the CsPbI2Br PSC efficiency and stability.