Visualization and Investigation of Charge Transport in Mixed-Halide Perovskite via Lateral-Structured Photovoltaic Devices

Mixed-halide perovskites, CH₃NH₃PbI_{3− x}Cl_x, can be used to fabricate highly efficient perovskite solar cells; the presence of chlorine ions affects the perovskite morphology and enhances optoelectronic properties. However, the reported device performances of mixed-halide perovskites are comparable to those of triiodide perovskites, CH₃NH₃PbI₃. Thus, the benefits of the presence of Cl⁻ ions in mixed-halide perovskites are uncertain. To clarify the effects of Cl⁻ on the optoelectronic properties of perovskite devices, a suitable device structure is required. In this study, lateral-structured perovskite devices are fabricated and their electrical properties are investigated. A clear contrast is found between the optoelectronic properties of the mixed-halide and triiodide perovskite; a suitable platform is also constructed for the spectroscopic analysis. Scanning photocurrent spectroscopy is used to visualize the charge carrier diffusion in the perovskite films and it is found that the charge carrier diffusion length of the mixed-halide perovskite is longer. It is also demonstrated by using conducting atomic force microscopy that the charge carrier pathways in the mixed-halide perovskite are more efficient, which means that it has longer charge carrier recombination life-times and higher photocurrents. This lateral-structured device has an architecture that makes it suitable for the observation of charge carrier diffusion and spectroscopic analysis.