Tuning substrate temperature for enhanced vacuum-deposited wide-bandgap perovskite solar cells: insights from morphology, charge transport, and drift-diffusion simulations

The efficiency of vacuum-processed perovskite solar cells lags behind that of solution-processed devices, partially because of the limited spectrum of deposition parameters that can be controlled during deposition. Substrate temperature is in principle a powerful tool to control the condensation and crystallization of thin films, but has been scarcely investigated for perovskites. This study systematically investigates the effect of substrate temperature on the deposition of the wide-bandgap perovskite Cs_0.2FA_0.8Pb(I_0.8Br_0.2)₃. We observe temperature-dependent morphological changes linked to variations in the adhesion coefficient of formamidinium iodide. Optical, structural, and optoelectronic analyses reveal that increasing the substrate temperature from -20 °C to 75 °C enhances charge carrier mobility and recombination lifetime by an order of magnitude. However, these improvements do not directly translate into better device performance due to competing factors such as morphology, interface energetics, and trap densities. Using drift-diffusion simulations, we identify key performance-limiting parameters, including ion mobility and charge trapping at interfaces and in the bulk. By optimizing the organic/inorganic deposition rate at -20 °C, we achieve state-of-the-art efficient wide-bandgap perovskite solar cells with enhanced thermal stability. This study highlights substrate temperature as a crucial parameter for improving material quality and device performance in vapor-deposited perovskites.