Experimental Determination of Complex Optical Constants of Air-Stable Inorganic CsPbI3 Perovskite Thin Films

Air-stable inorganic cesium lead iodide (CsPbI3) perovskite thin films with a bandgap of 1.7eV are a promising candidate for tandem cell solar cells, comprising a perovskite top cell with a crystalline silicon bottom cell. The device design and simulations are important to develop high-efficiency photovoltaic devices. However, knowledge of complex optical constants of the CsPbI3 thin f ilms is mandatory to complement such tasks. Herein, air-stable inorganic CsPbI3 perovskite thin films are prepared using one-step synthesis through a spin coating method. Variable angle spectroscopic ellipsometry (VASE) is then con ducted at five angles (43.9 , 48.9 , 53.9 , 58.9 , and 63.9 ) to obtain ellipso metric data (Ψ and Δ). The thickness nonuniformity model of the perovskite thin f ilm combined with an effective medium approximation for describing rough surface is adopted to achieve excellent fitting. The complex optical constants of the CsPbI3 thin film are experimentally obtained in the wavelength range of 300–1200 nm. The present results open the door for design and simulations on high-efficiency CsPbI3/c-Si tandem solar cells.