Interlayer engineering via alkaline hypophosphates for efficient and air-stable perovskite solar cells

Abstract

The energy level mismatch and unfavorable interfacial reaction between nickel oxide (NiO_x) and organic cations of the perovskite are the main factors affecting the power conversion efficiency (PCE) of inverted perovskite solar cells. Herein, interlayer engineering via dual-functional alkaline hypophosphite is introduced between the nickel oxide hole transport layer (HTL) and the perovskite layer. The introduction of alkaline hypophosphite deepens the valence band maximum of NiO_x, which better aligns the energy band of perovskite solar cells with the best energy level matching using sodium hypophosphite. In addition, the deposition of alkaline sodium hypophosphite on NiO_x reduces the proportion of Ni³⁺ and slows down the accelerated degradation of the perovskite layer caused by the reaction of excess Ni³⁺ with organic cations in the perovskite. The open-circuit voltage (V_OC) of devices treated with sodium hypophosphite increased from 1.01 to 1.08 eV with a power conversion efficiency of 19.92%. Moreover, the unencapsulated devices retained 80% efficiency for 1000 hours under ambient conditions (50–60% relative humidity), and demonstrate a feasible and effective strategy for the fabrication of efficient and air-stable inverted perovskite solar cells.