Cadmium ion soaking treatment and defect characterizations of hydrazine processed CISS photovoltaic cells

Solution-processed CuInS_xSe_2-x (CISS) solar cells are becoming an important research field. In addition to the promising device performance, this unique process will enable low cost and high throughput fabrication methods. We have previously demonstrated a hydrazine based CuInS_xSe_2-x solar cell fabrication approach with a maximum heating temperature of 390°C. In the present work, we introduce a cadmium ion soaking step into the fabrication process. This step significantly improves the open circuit voltage of the devices as well as the diode reverse saturation current and series resistance. We have studied the defect behavior in cadmium ion treated devices with several characterization techniques, including admittance spectroscopy, capacitance-voltage profiling and drive level capacitance profiling. We find that the cadmium ion soaking process can increase the charge carrier concentration in the bulk of the absorber, and reduce the activation energy of the most significant defect level present within the material.