A New Perspective on the Role of A-site Cation in Perovskite Solar Cells

TL;DR

This paper reveals that A-site cations in perovskite solar cells influence carrier transport by modulating electron-phonon interactions, offering a new approach to enhance efficiency.

Contribution

It introduces a novel understanding of how A-site cations affect electron-phonon coupling, guiding the design of more efficient perovskite solar cells.

Findings

Lower electron-phonon coupling with specific organic cations.

Coordination to halide ions reduces scattering.

Potential for improved power efficiency in PSCs.

Abstract

As the race towards higher efficiency for inorganic/organic hybrid perovskite solar cells (PSCs) is becoming highly competitive, a design scheme to maximize carrier transport towards higher power efficiency has been urgently demanded. Here, we unravel a hidden role of A-site cation of PSCs in carrier transport which has been largely neglected, 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 ion. 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 lower electron-phonon coupling by several promising organic cations including hydroxyl-ammonium cation (NH$_3$OH$^+$) and possibly Li$^+$ solvating methylamine (Li$^+$NH$_2$CH$_3$) than methyl-ammonium cation. A new perspective on the role of A-site cation could help in improving power efficiency and accelerating the application of PSCs.