Researchers from Peking University, Tsinghua University, Beijing Institute of Technology and Ecole Polytechnique Fédérale de Lausanne (EPFL) have tackled a reproducibility challenge in black-phase formamidinium lead iodide (α-FAPbI3) perovskites. They explained that while this is the desired phase for photovoltaic applications, water can trigger formation of photoinactive impurity phases such as δ-FAPbI3. The team found that the classic solvent system for perovskite fabrication exacerbates this reproducibility issue.
Growth of the photoactive black phase of formamidinium lead iodide (α-FAPbI3) usually requires dimethyl sulfoxide solvent, but the hygroscopic nature of this chemical also promotes water-induced degradation to the photoinactive phase. the scientists showed that a larger chlorinated organic molecule can form a hydrophobic capping layer that enables perovskite crystallization under humid conditions by protecting growing crystallites from water.
Solar cells were fabricated across a relative humidity range of 20-60% and reached power conversion efficiencies of 23.4% at 80% relative humidity.
An unencapsulated device retained 96% of its initial performance in humid air after 500 hours of illumination at maximum power point operation.
