CH₃NH₃Cl-Assisted One-Step Solution Growth of CH₃NH₃PbI₃: Structure, Charge-Carrier Dynamics, and Photovoltaic Properties of Perovskite Solar Cells

We demonstrate a novel one-step solution approach to prepare perovskite CH₃NH₃PbI₃ films by adding CH₃NH₃Cl (or MACl) to the standard CH₃NH₃PbI₃ precursor (equimolar mixture of CH₃NH₃I and PbI₂) solution. The use of MACl strongly affects the crystallization process of forming pure CH₃NH₃PbI₃, leading not only to enhanced absorption of CH₃NH₃PbI₃ but also to significantly improved coverage of CH₃NH₃PbI₃ on a planar substrate. Compared to the standard one-step solution approach for CH₃NH₃PbI₃, using MACl improves the performance of CH₃NH₃PbI₃ solar cells from about 2% to 12% for the planar cell structure and from about 8% to 10% for the mesostructured device architecture. Although we find no significant effect of using MACl on charge transport and recombination in mesostructured perovskite cells, the recombination resistance for planar cells increases by 1–2 orders of magnitude by using MACl. These results suggest that this new one-step solution approach is promising for controlling CH₃NH₃PbI₃ growth to achieve high-performance perovskite solar cells.