Optimization of indium tin oxide by pulsed DC power on single junction amorphous silicon solar cells

We investigated the optimal deposition conditions of a thin indium tin oxide (ITO) film on an amorphous silicon (a-Si) single-junction solar cell using pulsed DC magnetron sputtering. Thin ITO films were deposited while power, deposition time, pressure, gas flow and temperature were varied to find such conditions. The efficiency of a-Si solar cells with ITO films was 6.65% at the optimal conditions - a pulsed DC power of 40 W, a deposition time of 460 s, a pressure of 0.53 Pa, gas flow of 16 sccm and 151 °C. On the other hand, an a-SiGe tandem solar cell with the ITO films made at the optimal conditions yields an efficiency of 7.20%. We have also examined the surface morphology of ITO coated a-Si solar cells, using atomic force microscopy. Interestingly, a change in power does not alter the surface morphology at small length scales, whereas at large scales, the lower power sample had a lower surface roughness than the samples made with higher powers. We also find that for the range of deposition conditions examined, the value of the roughness exponent does not change with α ≃ 2/3 and a thin layer of ITO does not modify the surface morphology significantly.