Influence of Film Thickness on the Electronic Band Structure and Optical Properties of P–I–N CH₃NH₃PbI_3−xCl_x Perovskite Solar Cells

The phenomenal optoelectronic properties of lead halide perovskites have spurred a remarkable worldwide effort to develop them as photovoltaic materials. The morphology and crystal structure of the films have a profound effect on the characteristics and performance of devices; however, the influence of underlying hole transport layers (HTLs) or electron transport layers (ETLs) and film thickness on the film morphology and electronic characteristics remains unclear. Herein, the characteristics of perovskite films with variable thickness are studied, including the morphological, crystal, optical properties and electronic band structure of these films using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–vis absorption spectra. The corresponding performance of perovskite solar cells (PSCs) devices is correlated with the different thicknesses of perovskite films. In addition, ultraviolet photoelectron spectroscopy (UPS) results show that for the optimized perovskite thickness (310 nm) the interfacial dipole (Δ) formed at the interface with the substrate reaches its highest value of 0.23 eV. Therefore, this strong dipole compared with other thicknesses allows the carriers to be swept out efficiently.