Towards low-temperature processing of efficient γ-CsPbI 3 perovskite solar cells.

Inorganic cesium lead iodide (CsPbI 3 ) 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 3 PSCs at lower temperatures than was previously possible by introducing the long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI 2 ) and regulating the content of lead acetate (Pb(OAc) 2 ) in the perovskite precursor solution. We find that EDAI 2 acts as an intermediate that can promote the formation of γ-CsPbI 3 , while excess Pb(OAc) 2 can further stabilize the γ-phase of CsPbI 3 perovskite. Consequently, improved crystallinity and morphology and reduced carrier recombination are observed in the CsPbI 3 films fabricated by the new method. By optimizing the hole transport layer of CsPbI 3 inverted architecture solar cells, we demonstrate efficiencies of up to 16.6%, surpassing previous reports examining γ-CsPbI 3 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 2 and Pb(OAc) 2 in stabilizing γ-CsPbI 3 PSCs.