Halide perovskite materials have garnered significant attention for their potential in diverse applications such as solar cells, photodetectors, lasers and photocatalysis. CsPbBr₃, an all-inorganic metal halide perovskite, exemplifies this potential with its impressive stability against moisture and light [1]. With a direct band gap of 2.3 eV, large atomic number and high light-electron conversion efficiency, CsPbBr₃ is particularly suitable for high-energy radiation detection [2]. The material’s versatility extends to photovoltaics [3] and multicolour LEDs [4] through partial or total substitution of the bromide anion with iodide and/ or chloride. Device performance in polycrystalline films, which are typically produced via solution-based or vapour deposition methods, is greatly affected by the density of grain boundaries. In general a negative effect is attributed to grain boundaries due to an increased number of recombination sites, pathways for ion migration and openings for perovskite degrading species like oxygen [5]. Conversely, Luchkin et al. reports grain boundaries to be the primary location for photocarrier generation and transport, which can enhance device performance [6]. Therefore, controlling the deposition process to manage grain morphology and relating to the film performance is essential for the device optimization.   

In this study, we employ the hardly explored close space sublimation (CSS), a fast and scalable physical vapour deposition technique, to fabricate polycrystalline CsPbBr3 films [7]. Understanding the growth of CsPbBr₃ can serve as a model for other perovskite materials, contributing to advancements in thin film solar cells and light emitting applications. This solvent free synthesis route enables rapid growth rates up to 6 µm/min with a high material utilization of 98%. Single-phase CsPbBr₃ films are achieved across a wide range of deposition parameters. By separately adjusting the deposition conditions (substrate and source temperature, pressure), we access different growth regimes, enabling tunable grain sizes in the films without additional treatment.

Our study focuses on characterizing films with thicknesses of 1 – 10 µm and varying grain sizes. Using electrical and optical characterization methods like current – voltage characteristics, conductive atomic force microscopy, scanning electron microscopy, Raman and photoluminescence spectroscopy we correlate the optoelectronic properties with film morphology and grain structure. Taking advantage of the grain tunability offered by CSS, we aim at exploring the effect of grain size on the optoelectronic properties of CsPbBr₃, which is crucial for the optimization of perovskite-based device performances.