Photovoltaic Devices Using Sublimed Methylammonium Lead Iodide Perovskites: Long-Term Reproducible Processing

Abstract

Fully evaporated solar cells using methylammonium iodide (MAI)-based perovskites can reach power conversion efficiencies exceeding 20%. An important point to advance perovskite photovoltaics is to ensure reproducibility from batch to batch. Sublimation control of organic ammonium halides is critical in achieving this for evaporated perovskite solar cells. Herein, a reproducible procedure for the coevaporation of PbI2 and MAI based on an evaporator chamber setup with only two quartz crystal microbalances (QCMs) is described. One QCM monitors exclusively the PbI2 precursor (PbI2-QCM) and the second QCM monitors the total amount of MAPbI3 mass reaching the substrates (MAPbI3-QCM). It is shown that the MAI evaporation can be reliably monitored, indirectly, through the MAPbI3-QCM. In this way, the fluctuating sublimation rates usually observed due to variations of MAI purity are avoided. This allows one to obtain consistently high-performing solar cells over a period of one and a half years.