Electrical Impedance Characterization of CdTe Thin Film Solar Cells with Hydrogen Iodide Back Surface Etching

Thin film CdTe solar cells were prepared using close-space sublimation followed by a standard cadmium chloride activation annealing treatment. After the activation process, some of the samples were subjected to a brief etching process using a 10% hydrogen iodide solution in methanol while the others were only rinsed with methanol. Completed solar cells from both sample types were prepared and characterized using current and capacitance-voltage scanning methods. The results show that the etching process increases the open circuit voltage by 10-20mV and the fill factor by 1-5% compared to the devices without the etching, thus increasing the efficiency from ~13% to ~15%. Capacitance-voltage measurements indicate that the bulk carrier (hole) density of the CdTe films increase by approximately a factor of three, which could partially explain the increase in device performance. The cause of the change in carrier density is still under investigation.