Towards low-temperature processing of efficient γ-CsPbI₃ perovskite solar cells

Inorganic cesium lead iodide (CsPbI₃) 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-CsPbI₃ PSCs at lower temperatures than was previously possible by introducing the long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI₂) and regulating the content of lead acetate (Pb(OAc)₂) in the perovskite precursor solution. We find that EDAI₂ acts as an intermediate that can promote the formation of γ-CsPbI₃, while excess Pb(OAc)₂ can further stabilize the γ-phase of CsPbI₃ perovskite. Consequently, improved crystallinity and morphology and reduced carrier recombination are observed in the CsPbI₃ films fabricated by the new method. By optimizing the hole transport layer of CsPbI₃ inverted architecture solar cells, we demonstrate efficiencies of up to 16.6%, surpassing previous reports examining γ-CsPbI₃ 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 EDAI₂ and Pb(OAc)₂ in stabilizing γ-CsPbI₃ PSCs.