Quasi-Two-Dimensional Perovskite Solar Cells with Efficiency Exceeding 22%

Quasi-two-dimensional (quasi-2D) perovskites have attracted attention because they have better stability than the 3D counterpart. However, power conversion efficiency of perovskite solar cells (PSCs) based on quasi-2D perovskite still lags behind those of the devices with 3D perovskites. We report here on a quasi-2D PSC employing an alternating cation perovskite of multidimensional hybrid GA(MA)_nPb_nI_3n+1 (n = 5) with a PCE over 22%, which is enabled by post-treatment with amphoteric imidazolium iodide (ImI). An optimal concentration of ImI reduces trap density and enhances charge mobility because of the improved phase purity and crystallinity, which eventually leads to a PCE of 22.26% with an open-circuit voltage of 1.19 V, a fill factor of 0.81, and a short-circuit current density of 22.99 mA/cm². Moreover, a light-soaking stability test shows that ca. 94% of initial PCE is maintained after over 1200 h. The PCE achieved in this work is a record among the reported quasi-2D PSCs.