Impact of the Cd2+ treatment on the electrical properties of Cu2ZnSnSe4 and Cu(In,Ga)Se2 solar cells

The present contribution aims at determining the impact of modifying the properties of the absorber/buffer layer interface on the electrical performance of Cu2ZnSnSe4 (CZTSe) thin-film solar cells, by using a Cd2+ partial electrolyte (Cd PE) treatment of the absorber before the buffer layer deposition. In this work, CZTSe/CdS solar cells with and without Cd PE treatment were compared with their respective Cu(In,Ga)Se-2 (CIGSe)/CdS references. The Cd PE treatment was performed in a chemical bath for 7min at 70 degrees C using a basic solution of cadmium acetate. X-ray photoemission spectroscopy measurements have revealed the presence of Cd at the absorber surface after the treatment. The solar cells were characterized using current density-voltage (J-V), external quantum efficiency, and drive-level capacitance profiling measurements. For the CZTSe-based devices, the fill factor increased from 57.7% to 64.0% when using the Cd PE treatment, leading to the improvement of the efficiency () from 8.3% to 9.0% for the best solar cells. Similar observations were made on the CIGSe solar cell reference. This effect comes from a considerable reduction of the series resistance (R-S) of the dark and light J-V, as determined using the one-diode model. The crossover effect between dark and light J-V curves is also significantly reduced by Cd PE treatment. Copyright (c) 2015 John Wiley & Sons, Ltd.