Fabrication of High-Quality CsPbI3 Perovskite Films with Phosphorus Pentachloride Additive for Highly Stable Solar Cells

Fully inorganic perovskite cesium lead triiodide (CsPbI3) has garnered much attention from researcher for photovoltaic application because of its excellent thermal stability compared with the inorganic-organic hybrid counterparts, along with the potential to serve as the top cell in tandem devices with silicon solar cell. However, the active alpha-phase cubic CsPbI3 spontaneously tends to transform into the non-perovskite delta-CsPbI3 when subjected to ambient condition. This work proposes an effective method to fabricate high-quality and stable alpha-phase cubic CsPbI3 films by introducing phosphorus pentachloride (PCl5) as an additive. PCl5 acts as colloidal binder for modulating crystallization dynamics of perovskites, resulting in high-quality film and a significantly suppressed phase transition. Finally, highly stable CsPbI3 perovskite solar cells can be achieved with a power conversion efficiency up to 17.85 %, and a long-term stability in N-2 filled glove box.