Air-Stable Hybrid Perovskite Solar Cell by Sequential Vapor Deposition in a Single Reactor
Siphelo Ngqoloda, Christopher J. Arendse, T.F.G. Muller, P. F. Miceli, S. Guha, Louise Mostert, Clive J. Oliphant
Abstract
We demonstrate a facile two-step low-pressure vapor deposition of methylammonium lead iodide (MAPbI3) perovskite films in a single reactor. Continuous, polycrystalline lead iodide (PbI2) films were deposited in the first step and successfully converted to high quality perovskite films in the second step during exposure of PbI2 films to methylammonium iodide (MAI) vapor. A complete conversion was realized after 90 min of exposure with an average grain size of 3.70 ± 1.80 μm. The perovskite conversion starts at the PbI2 surface through the intercalation reaction of PbI2 and MAI vapor molecules and progresses toward the PbI2/substrate interface. The coverage and quality of the perovskite thin film are controlled by that of the predeposited PbI2 film. The absorbance measurements confirmed air stability of the fully converted perovskite for 21 days, ascribed to its superior morphology and grain size. Finally, a planar single-junction perovskite solar cell with no additives or additional interfacial engineering was fabricated and tested under open-air conditions, yielding a best power conversion efficiency of 11.7%. The solar cell maintains 85% of its performance up to 13 days in the open air with a relative humidity up to 80%.