Pure Iodide Multication Wide Bandgap Perovskites by Vacuum Deposition

The CsPbI₃ perovskite has a suitable bandgap (≈1.7 eV) for application in tandem solar cells. One challenge for this compound is that the semiconducting perovskite phase is not stable at room temperature, when it tends to form a yellow nonperovskite phase with a bandgap of approximately 2.8 eV. Therefore, many reports have been focused on the stabilization of the CsPbI₃ black perovskite phase through the use of additives during solution processing. Vacuum deposited CsPbI₃ has been seldom reported, as in this case, the insertion of stabilizing agents is more challenging. In this work, we demonstrate the vacuum processing of CsPbI₃ perovskite films at room temperature, obtained by incorporating dimethylammonium iodide by cosublimation with CsI and PbI₂. As-prepared films were applied in planar solar cells, leading to an average power conversion efficiency (PCE) exceeding 12%. In order to improve the device performance, we introduced a third A-site cation (methylammonium) in a four-source deposition process. This pure iodide formulation can be used in wide bandgap solar cells with a PCE up to 14.8%.