A New Perspective on the Role of A‐Site Cations in Perovskite Solar Cells

Abstract

As the race toward higher efficiency for inorganic/organic hybrid perovskite solar cells (PSCs) is becoming highly competitive, a design scheme to maximize carrier transport toward higher power efficiency has been urgently demanded. In this study, a hidden role of A-site cations of PSCs in carrier transport, which has been largely neglected is unraveled, i.e., tuning the Frohlich electron-phonon (e-ph) coupling of longitudinal optical (LO) phonon by A-site cations. The key for steering Frohlich polaron is to control the interaction strength and the number of proton (or lithium) coordination to halide ions. The coordination to I- alleviates electron-phonon scattering by either decreasing the Born effective charge or absorbing the LO motion of I. This novel principle discloses low electron-phonon coupling in several promising organic cations including hydroxyl-ammonium cation (NH3OH+), hydrazinium cation (NH3NH2+) and possibly Li+ solvating methylamine (Li+center dot center dot center dot NH2CH3), on a par with methyl-ammonium cations. A new perspective on the role of A-site cations could help in improving power efficiency and accelerating the application of PSCs.