Chelating diamine surface modifier enhances performance and stability of lead halide perovskite solar cells

Abstract

Mono- or di-ammonium cations are commonly used to enhance the performance and stability of perovskite solar cells (PSCs) via surface defect passivation. However, their effectiveness is still limited by the little understanding of the structure–property-performance relationship of the capping layer/3D perovskite stack. In this work, two diamine spacers with similar chemical composition but different molecular geometry are tested: 4,4′-Dithiodianiline (2S) and 4,4′-Ethylenedianiline (ET). In 2S, the two amine groups are spatially close owing to a torsion in the backbone of the molecule. Instead, in ET the amine groups are at the maximum distance. The torsion allows 2S to bind to neighboring vacancy sites at the surface of the perovskite lattice, enhancing its passivation capabilities with respect to ET. The 2S spacer forms a 2D metal halide phase at the perovskite surface, which offers better charge extraction properties than the 1D phase induced by ET spacer. In solar cells incorporating 2S, these properties result in a power conversion efficiency (PCE) of 20.72 %, improved from the 18.36 % PCE of the reference and almost no loss of efficiency after 1000 h under constant illumination in inert atmosphere.