Effect of Processing Medium and Condition on Absorption Enhancement of Femtosecond Laser Treated a-Si:H Thin Film

Abstract

ABSTRACT Hydrogenated amorphous silicon (a-Si:H) thin films have been considered for use in solar cell applications because of their significantly reduced cost compared to crystalline bulk silicon, however, their overall efficiency and stability are less than that of their bulk crystalline counterparts. Limited work has been performed on simultaneously solving the efficiency and stability issues of a-Si:H. Surface texturing and crystallization on a-Si:H thin film can be achieved through one-step femtosecond laser processing, which can potentially alleviate the disadvantages of a-Si:H in solar cell applications. In this study, submicrometer conical and pillar-shaped spikes are fabricated by irradiating a-Si:H thin films deposited on glass substrates with hundreds of 800nm-wavelength, 130fs-duration laser pulses in air and water environments, respectively. Enhanced light absorption is observed due to light trapping based on surface geometry changes, while the formation of a mixture of hydrogenated nanocrystalline silicon (nc-Si:H) and a-Si:H after crystallization suggests that the overall material stability can potentially be increased. The relationship between crystallinity, fluence and scanning speed is also discussed. Furthermore, a comparison of absorptance spectra for various surface morphologies is performed. Finally, absorptance measurements across the solar spectrum show that the combination of surface texture and crystallinity induced by femtosecond laser processing is very promising for a-Si:H thin film solar cell applications