Failure Mechanisms of Fluorine-Doped Tin Oxide Thin Films in Glass and Reliability Tests

Fluorine-doped tin oxide (FTO) is a transparent conductive oxide that is used in solar cells and energy devices. In this study, environmental tests and corresponding failure analyses were conducted to identify the failure mechanisms of FTO. An FTO thin film was prepared via spray pyrolysis deposition (SPD). Environmental tests were conducted in high-temperature and high-humidity environments, similar to field conditions. The degradation behavior and failure mechanisms were investigated using Hall-coefficient measurements, X-ray powder diffraction (XRD) analysis, and field-emission scanning electron microscopy (FE-SEM), before and after exposure to the test environments. A decrease in the carrier concentrations and electron mobilities of the FTO samples was observed after the tests. The analysis of the results revealed a decrease in the F concentration after the tests, resulting in a decrease in the carrier concentration. Moreover, the electron mobility decreased owing to the reduction in periodicity of the crystal attributed to F vacancies. Therefore, high-temperature and high-humidity conditions significantly decreased the durability of FTO. Future studies should consider the degradation of F in such environments and determine ways to prevent it.