Enhancing photovoltaic performance of GeSe thin film solar cells by photogenerated carriers redistribution via Cu doping

Germanous selenide (GeSe) is an emerging photoactive layer material due to its excellent photoelectric properties, low cost and environmental friendliness. However, severe carrier recombination in the GeSe photoactive layer remains a significant factor limiting the conversion efficiency of GeSe solar cells. In this study, the GeSe photoactive layers were doped copper chloride (CuCl 2 ) solution, enabling the distribution of Cu 2+ ions throughout the layer, primarily accumulating on the GeSe grain surface. Its impact on the carrier transport in the GeSe photoactive layer was studied by ultraviolet photoelectron spectroscopy, kelvin probe force microscopy, and transient photovoltage. The doping can not only increase the Fermi level of the GeSe, but also adjust the local built-in potential on grain boundaries, so that the charge carriers can be redistributed in the three-dimensional space. Notably, at the grain boundaries, the hole flow before doping changes to electron flow, effectively reduces the recombination probability of charge carriers, and increases the carrier lifetime from 200.23 to 374.57 μs. As a result, the conversion efficiency after processing with CuCl 2 is increased from 1.98 % to 3.01 %. This study provides a reference for understanding the carrier kinetics in GeSe solar cells to improve the photoelectric conversion performance of the device.