THERMAL STABILITY OF NOVEL HOLE-SELECTIVE CONTACTS FOR SILICON WAFER SOLAR CELLS

The thermal stability of novel hole selective contacts is of key importance when integrating these films into high-efficiency silicon solar cells. In this work, we focus on the thermal stability of atomic layer deposited (ALD) WOx with and without an a-Si:H interface passivation layer. Hydrogen diffusion from a-Si:H to WOx layer was detected by both Fourier transform infrared spectroscopy and in-situ ultraviolet photoelectron spectroscopy for annealing temperatures above 180 o C. The work function decreased for higher annealing temperatures, but the decrease was slightly less for the samples with the a-Si:H interface passivation layer due to the H doping of WOx. An annealing temperature higher than 223 ºC results in insufficient workfunction for hole selectivity. In terms of surface passivation, it was found that the plasma-enhanced ALD of WOx introduced some plasma damage on the a-Si:H layer as was detected by injection-dependent effective lifetime measurement. Fortunately, this could be recovered by an annealing treatment at 220 ºC, resulting in an implied VOC of 730 mV. The results provide a promising potential of the implementation on ALD WOx for high-efficiency silicon solar cells.