Towards low-temperature processing of efficient γ-CsPbI perovskite solar cells.

Inorganic cesium lead iodide (CsPbI) perovskite solar cells (PSCs) have attracted enormous attention due to their excellent thermal stability and optical bandgap (∼1.73 eV), well-suited for tandem device applications. However, achieving high-performance photovoltaic devices processed at low temperatures is still challenging. Here we reported a new method for the fabrication of high-efficiency and stable γ-CsPbI PSCs at lower temperatures than was previously possible by introducing the long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI) and regulating the content of lead acetate (Pb(OAc)) in the perovskite precursor solution. We find that EDAI acts as an intermediate that can promote the formation of γ-CsPbI, while excess Pb(OAc) can further stabilize the γ-phase of CsPbI perovskite. Consequently, improved crystallinity and morphology and reduced carrier recombination are observed in the CsPbI films fabricated by the new method. By optimizing the hole transport layer of CsPbI inverted architecture solar cells, we demonstrate efficiencies of up to 16.6%, surpassing previous reports examining γ-CsPbI in inverted PSCs. Notably, the encapsulated solar cells maintain 97% of their initial efficiency at room temperature and under dim light for 25 days, demonstrating the synergistic effect of EDAI and Pb(OAc) in stabilizing γ-CsPbI PSCs.