Minimizing Voltage Deficit in Methylammonium-Free Perovskite Solar Cells Via Surface Reconstruction

Methylammonium-free perovskite solar cells have attracted a great deal of attention owing to the optimal bandgap towards the Shockley-Queisser optimum and the improved thermal stability of FAPbI3 based perovskite. Nevertheless, MA-free devices suffer from a large voltage deficit further limiting the improvement of performance. Herein, a surface reconstruction strategy to constituted 2D/3D heterojunction via imidazole hydrobromide post-treatment is proposed. The formation 2D/3D heterostructure endows the MA-free perovskite film with decent energy-level alignment and reduced non-radiative recombination, which enhances the quasi-Fermi level splitting further to minimize the voltage deficit in the device. Consequently, this strategy leads to a significantly increased power conversion efficiency of 23.25% for FA0.9Cs0.1PbI3 perovskite solar cells, along with an optimal voltage deficit of 0.384 V. This work may trigger the development of surface reconstruction that constitutes suitable interface to the perovskite film to maximize the open-circuit voltage and thus the power conversion efficiency of perovskite solar cells.