Comprehensive study of the two-step solution processes in ambient air for lead iodide perovskite solar cells

Organic-inorganic lead halide perovskite solar cells have attracted a great deal of interest because of potential low cost and high efficiency. However, in most publications, solar cells were fabricated in a highly controlled environment (glove boxes). Only a few papers reported fabrication of solar cells in air with the maximum efficiency of ~15%. We carried out comprehensive study of the two-step solution process parameters for fabrication of perovskite solar cells in ambient air including PbI₂ spin coating speed, mesoporous TiO₂ spin coating speed, hole transport material (HTM) spin coating speed, and HTM exposure to air etc. We found that the higher spin speed of PbI₂ is critical for high-quality PbI₂ film formation. The HTM exposure to air is also important to fabricate solar cells with larger current density and better fill factors.