Large-grained formamidinium-based films via a 2D–3D conversion mechanism for high-performance perovskite solar cells without anti-solvent

Abstract

High quality and uniform dense perovskite films are essential to exciton dissociation and charge transportation in perovskite solar cells (PSCs). Although MA_1−xFA_xPbI₃ planar films can be fabricated by a solution process with chlorobenzene anti-solvent, the fabrication still suffers from problems such as environmental pollution, high cost and low reproducibility. In this work, we present a HI and MACl assisted 2D–3D conversion mechanism (HI-MACl ACM), defined as an anti-solvent-free method, to fabricate pure phase MA_1−xFA_xPbI₃ and enhance the quality of perovskite films. The intermediate 2D HMA_1−xFA_xPbI₃Cl derived from HI-MACl ACM eventually transforms to 3D MA_1−xFA_xPbI₃ perovskite. This 2D structure also has an impact on retarding nucleation. The obtained films were composed of highly crystallized and large grains (over 1000 nm), which minimized grain boundaries and trap sites, giving a power conversion efficiency above 18.86% in PSCs.