Stabilizing all-inorganic CsPbI3 perovskite films with polyacrylonitrile for photovoltaic solar cells

Abstract

A solution-processed CsPbI₃ perovskite film usually suffers from nonuniform crystallization owing to its inorganic components, leading to its poor surface morphology and various defects on the surface and grain boundaries. Herein, polyacrylonitrile (PAN) was employed as a defect passivator for CsPbI₃ perovskite films. The nitrile (CN) groups on the side chains of the PAN chain skeleton could passivate an undercoordinated Pb ion with a partial positive charge by donating their lone pair of electrons from the N atom, decreasing the density of defect states and enhancing the energy barrier of phase transition. In addition, the incorporation of PAN triggered the nucleation of the perovskite precursor, leading to the formation of a dense CsPbI₃ perovskite film with high coverage. Moreover, the robust PAN in the perovskite film enhanced the thermal and water resistance properties of the perovskite film. As a result, the unencapsulated CsPbI₃ perovskite cells exhibited superior thermal and humidity stability with 16.21% power conversion efficiency. This work provides a liable polymer passivator to further improve both the efficiency and stability of CsPbI₃-based solar cells.