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

Fully inorganic perovskite cesium lead triiodide (CsPbI ) 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 α-phase cubic CsPbI spontaneously tends to transform into the non-perovskite δ-CsPbI when subjected to ambient condition. This work proposes an effective method to fabricate high-quality and stable α-phase cubic CsPbI films by introducing phosphorus pentachloride (PCl ) as an additive. PCl acts as colloidal binder for modulating crystallization dynamics of perovskites, resulting in high-quality film and a significantly suppressed phase transition. Finally, highly stable CsPbI perovskite solar cells can be achieved with a power conversion efficiency up to 17.85 %, and a long-term stability in N filled glove box.