Using time-resolved in situ X-ray photoelectron spectroscopy, we identify and suppress rapid degradation mechanisms for cesium-stabilized formamidinium lead iodide perovskite materials used in state-of-the-art photovoltaics. Accelerated degradation under high light intensity and heating reveals a photocatalytic reaction pathway responsible for rapid decomposition in iodide-rich compositions and a slower pathway for more stoichiometric samples. Using Avrami−Erofe'ev kinetic analysis, we find that the fast process is consistent with a 2D crystallization and growth mechanism fueled by excess halide salt at grain boundaries and surfaces. Moreover, the rate of decomposition varies dramatically with the wavelength of light used to illuminate the thin films. Our results reveal the photodegradation mechanisms of PbI 2 and excess iodide and provide a path to increasing perovskite stability under photoexcitation.

Nickel-rich cathode materials are quickly becoming the next commercial cathode for electric vehicles; however, their long-term cycle life retention and air stability remain a barrier to the use of these lower-cost, higher-energy density materials. Surface reactivity and mechanical degradation, especially at high voltages, remain two issues that impede these material’s commercialization. While surface treatments have shown great promise in reducing surface reactivity, mechanical degradation or “cathode cracking” persists yet. In the present work, LiNi0.9Mn0.05Al0.05O2 (NMA) cathode materials are first pulverized into their primary particle constituents and then coated with lithium phosphate via solution-based chemistry with varying concentrations of phosphoric acid. The cathodes are characterized using energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, and electrochemical cycling. After 100 cycles, the pulverized NMA cathodes coated using the lowest concentration of phosphoric acid show delayed voltage decay and double the discharge capacity compared to the pristine material in full cells during high-voltage cycling.