Enhanced electrical characteristics of a-Si thin films by hydrogen passivation with Nd³⁺:YAG laser treatment in underwater for photovoltaic applications

Post deposition underwater treatment with a nanosecond Nd3+:YAG laser is proposed and demonstrated for the passivation of electrical defects in 400–1000 nm-thick a-Si thin films needed for solar cells. The proposed pulsed laser beam-overlap technique also allows simultaneous annealing and texturing. Atomic hydrogen, oxygen, and hydroxyl radicals activated by the breakdown of water by laser heating passivate the dangling bonds in the crystal grains, improving the solar cell performance. The presence of hydrogen observed after water annealing using X-ray photo electron spectroscopy (XPS), Raman spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) shows that the passivation improvement is caused by diffusion of atomic hydrogen. After underwater annealing, relative improvement in the life time of minority carriers was measured to be approximately 13% and the efficiency of n-aSi/p-cSi solar cells is found to be increased (~2 to 3%) when compared to that in air.