Pure 2H phase MoSe 2 nanosheets promote the formation of a porous PbI 2 film and modulate residual stress for highly efficient and stable perovskite solar cells

2D MoSe 2 nanosheets added to PbI 2 precursor solution in the process of preparing perovskite solar cells (PSCs) to improve conversion of PbI 2 and crystallinity of perovskite films as well as reduce residual stress. Optimal power conversion efficiency of 22.80% is achieved.