Interfacial engineering and film-forming mechanism of perovskite films revealed by synchrotron-based GIXRD at SSRF for high-performance solar cells

Organic-inorganic hybrid perovskites as promising light-harvesting materials have been the focus of scientific research and development of photovoltaics recently. Especially, metal halide perovskites currently become one of the most competitive candidates for the fabrication of solar cells with record certified efficiency over 25%. Despite the high efficiency, many fundamental questions remain unclear and need to be addressed at both the material and device levels, such as weaker stability, poorer reproducibility, easier degradation influenced by water, oxygen, thermal factors, and so on. Based on recent reports, interfacial engineering plays a crucial role in controlling the behavior of the charge carriers and in growing high quality, defect-free perovskite crystals, therefore helping to enhance device performance and operational stability. However, little attention has been paid to the interface interaction mechanism among carrier transport layers and perovskite active layer. It is extremely urgent to explore the perovskite interfaces in details and to find out how its interface structure is relative to the efficiency and hysteresis in perovskites solar cells. Based on the Shanghai Synchrotron Radiation Facility (SSRF), we have established an advanced perovskite photovoltaic device preparation and in-line test system, developed a series of unique surface diffraction analysis methods based on ex situ and in situ grazing incidence X-ray diffraction (GIXRD), and reported a large number of novel synchrotron radiation results on crystallization of the perovskite photovoltaics films. Our main investigations are aimed to deeply insitu study the perovskite film growth dynamics using synchrotron radiation GIXRD technology in combination with a customized mini online glove box (c(H2O,O-2)<1 ppm) and temperature-humidity control equipment, and so on., which should provide solid theoretical background and point to the useful direction for designing and fabricating high-performance perovskites solar cells. Moreover, a multifunctional joint characterization technology that in-situ GIXRD simultaneously combines with conventional characterization methods at synchrotron radiation beamline station must be put on the agenda in future research, which greatly promotes much more comprehensive and intuitive understanding of the nucleation, microcrystallization, and degradation mechanisms of perovskite heterojunction films, and therefore further optimizing their chemical synthesis strategies at the molecular level for functional materials. (C) 2020 The Author(s). Published by Elsevier Ltd.