Synergistic surface modulation with isotropic 2D GA2PbI4 and Lewis base enhances efficiency and stability of perovskite solar cells

Abstract

The commonly used post-treatment agents of large-cation ammonium salts for perovskite solar cells (PSCs) exhibit significant effectiveness but still encounter limitations, as a large spacing distance within the resulting two-dimensional (2D) perovskite could impede the vertical charge transport. Herein, we introduce a multifunctional agent of guanidinium acetate (GAAc), which exhibits a synergistic effect arising from the cation and anion on regulating the perovskite's defects. Specifically, the GA⁺ cation transforms into a 2D perovskite of GA₂PbI₄, which forms a type I heterojunction with the original 3D perovskite. In contrast to the traditional anisotropic layered 2D perovskite with a preferred out-of-plane orientation, GA₂PbI₄ showed an isotropic orientation, which contributes to more efficient carrier transport in the vertical direction. Additionally, the lone electron pairs of Ac⁻ can coordinate with Pb²⁺. The synergistic effect of the cation and anion suppresses the non-radiative charge recombination and improves the ion migration activation energy of perovskites. As a result, the GAAc-treated device achieved a remarkable power conversion efficiency (PCE) of 25.22%. When scaling up to an active area of 1 cm², the devices still achieved a PCE of 24.18%. Moreover, the optimized device showed a T₈₀ operational lifetime of 2073 hours at the maximum power point tracking.