TY - GEN A1 - Gawlińska-Nęcek, Katarzyna A1 - Kot, Małgorzata A1 - Starowicz, Zbigniew A1 - Jarzębska, Anna A1 - Panek, Piotr A1 - Flege, Jan Ingo T1 - Instability of Formamidinium Lead Iodide (FAPI) Deposited on a Copper Oxide Hole Transporting Layer (HTL) T2 - ACS Applied Materials & Interfaces N2 - Copper oxide appears to be a promising candidate for a hole transport layer (HTL) in emerging perovskite solar cells. Reasons for this are its good optical and electrical properties, cost-effectiveness, and high stability. However, is this really the case? In this study, we demonstrate that copper oxide, synthesized by a spray-coating method, is unstable in contact with formamidinium lead triiodide (FAPI) perovskite, leading to its decomposition. Using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–vis) spectrophotometry, we find that the entire copper oxide diffuses into and reacts with the FAPI film completely. The reaction products are an inactive yellow δ-FAPI phase, copper iodide (CuI), and an additional new phase of copper formate hydroxide (CH2CuO3) that has not been reported previously in the literature. KW - formamidinium lead iodide KW - perovskites KW - instability KW - Cu2O KW - hole transporting layer KW - phase transition Y1 - 2024 U6 - https://doi.org/10.1021/acsami.4c03440 SN - 1944-8244 VL - 16 IS - 21 SP - 27936 EP - 27943 PB - American Chemical Society (ACS) ER -