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-performing photovoltaic devices processed at low temperatures is still challenging. Here we reported a new method to fabricate 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 up to 16.6% efficiencies, surpassing previous reports examining γ-CsPbI₃ in inverted PSCs. Notably, the encapsulated solar cells maintain 97% of their initial efficiency at room temperature and dim light for 25 days, demonstrating the synergistic effect of EDAI2 and Pb(OAc)2 on stabilizing γ-CsPbI₃ PSCs.