Revealing the Dynamics of the Thermal Reaction between Copper and Mixed Halide Perovskite Solar Cells
Jihoo Lim, Eun Young Choi, Moonyong Kim, Minwoo Lee, Daniel Chen, Martin A. Green, Jan Seidel, Changheon Kim, Jongsung Park, Xiaojing Hao, Jae Sung Yun
Abstract
Copper (Cu) is present not only in the electrode for inverted-structure halide perovskite solar cells (PSCs) but also in transport layers such as copper iodide (CuI), copper thiocyanate (CuSCN), and copper phthalocyanine (CuPc) alternatives to spiro-OMeTAD due to their improved thermal stability. While Cu or Cu-incorporated materials have been effectively utilized in halide perovskites, there is a lack of thorough investigation on the direct reaction between Cu and a perovskite under thermal stress. In this study, we investigated the thermal reaction between Cu and a perovskite as well as the degradation mechanism by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Kelvin probe force microscopy (KPFM). The results show that high temperatures of 100 °C induce Cu to be incorporated into the perovskite lattice by forming “Cu-rich yet organic A-site-poor” perovskites, (CuxA1–x)PbX3, near the grain boundaries, which result in device performance degradation.