Electron-deficient 4-nitrophthalonitrile passivated efficient perovskite solar cells with efficiency exceeding 22%

Perovskite solar cells (PSCs) have achieved tremendous success in advancing high power conversion efficiencies. However, defect-induced recombination at grain boundaries (GBs) and the surface of polycrystalline perovskites seriously hinder the further performance enhancement and environmental stability of PSCs. Here, a simple passivating molecule, 4-nitrophthalonitrile (4NPN) with σ–π accepting nitro (–NO2) and cyano groups (–CN), was employed to passivate the charged defects in perovskites. The addition of electron-deficient 4NPN into the perovskite layer of PSCs could not only enhance VOC and the FF, leading to high PCE over 22% but also improved environmental stability. These improvements were attributed to the effective passivation of the defects in the perovskite film by the strongly polarized nitro/cyano groups. In addition, the electron-deficient 4NPN could slightly adjust the energy level of the perovskite facilitating more efficient hole transfer. This work demonstrates the role of strong electron-withdrawing nitro/cyano groups in passivating the vacancy-defects of perovskites and 4NPN as a simple passivator conducive to obtaining high-performance PSCs.