Multifunctional liquid additive strategy for highly efficient and stable CsPbI2Br all-inorganic perovskite solar cells

CsPbI2Br all-inorganic perovskite has attracted considerable attention due to its high thermal stability and suitable bandgap, while the unsatisfactory crystallization quality and moisture instability significantly hinder its further application. Herein, a novel multifunctional liquid additive, 2-hydroxyethyl methacrylate (HEMA), is introduced into the CsPbI2Br precursor to ameliorate the above issues. Our results demonstrate that the functional groups of HEMA can interact with perovskite precursor, thus improving crystallization and passivating defects at the same time, and leading to a champion power conversion efficiency of up to 16.13%. Importantly, HEMA molecule in perovskite films will polymerize to a hydrophobic polymer at grain boundaries through breaking C = C bonds during the high temperature annealing process (160 °C). Moreover, this multifunctional liquid additive strategy endows perovskite films with promoted moisture tolerance by crosslinking perovskite grains and blocking moisture penetration, thus the unencapsulated device maintains 78% of its initial efficiency after aging at 30% relative humidity for 1000 h. These results demonstrate that the additive engineering with multifunctional molecule is applicable strategy for developing CsPbI2Br all-inorganic perovskite solar cells with both high efficiency and stability.