Stabilizing perovskite solar cells at 85 °C via additive engineering and MXene interlayers

Abstract

An amorphous carbon-rich conductive phase formed at 85 °C and 1 sun operation, causing carrier shunt losses in perovskite solar cells, is mitigated by additives at grain boundaries. MXene-interlayer prevents delamination during thermal expansion. The commercialization of Perovskite Solar Cells (PSCs) is currently a reality. The detection of early instabilities, especially at high temperatures is vital for the successful widespread implementation of the technology. Commercial devices must sustain temperatures as high as 85 °C in order to surpass standardized tests and certification for the final PV product. However, in situ and operando stability analysis and detailed structural and electronic properties of full devices are still rarely found in the literature. In this work, we carried out in situ operational stability testing at 85 °C, complemented by in situ X-ray diffraction, impedance spectroscopy, photoluminescence, current–voltage measurements and electron microscopy. Our results demonstrate a large lattice expansion in the halide perovskite which provokes a clear voltage drop in the PSC. While no changes in lattice constants were observed over time at 85 °C, we noticed a reversible formation of an amorphous “carbon rich” surface shell material surrounding the perovskite grains. This material is linked to a decrease in shunt resistance, and the increase of ionic conductivity. The latter triggered the gradual photovoltaic performance loss observed in our PSC at high temperature. Additionally, we demonstrate the possibility to delay this PSC degradation by employing stability-enhancing methods such as additive engineering and the application of functionalized 2D Ti 3 C 2 MXene interlayers to the PSC. Our work showcases the value of complementing stability tests with advanced characterization, significantly showcasing the value of in operando structural studies.