Tailoring particle size of PbI 2 towards efficient perovskite solar cells under ambient air conditions.

PbI 2 films as templates are essential to the quality of perovskite (PVK) film in a two-step sequential deposition process. Herein, we demonstrate that PbI 2 microcrystal powder (P-PbI 2 ) of micrometer size is beneficial for preparing higher-quality PbI 2 films in contrast to millimeter-sized PbI 2 crystals (C-PbI 2 ) under low relative humidity (RH) conditions. Surprisingly, C-PbI 2 allowed the growth of denser films than P-PbI 2 under heavy RH conditions. Ultimately, P-PbI 2 gave PVK solar cells (PSCs) a best power conversion efficiency (PCE) of 23.30% under a low RH of 30 ± 5%, and C-PbI 2 derived an impressive PCE of 21.09% when fabricated under conditions with RH = 50 ± 5%. This work provides ideas for the selection of lead iodide for the fabrication of PSCs under air conditions.