Effect of hydrogen on surface texturing and crystallization of aSi:H thin film irradiated by excimer laser

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 a one-step laser processing, which can potentially alleviate the disadvantages of a-Si:H in solar cell applications. In this study, hydrogenated and dehydrogenated amorphous silicon thin films deposited on glass substrates were irradiated by KrF excimer laser pulses and the effect of hydrogen on surface morphologies and microstructures are discussed. The sharp micrometer spikes are only fabricated on a-Si:H surfaces, and the large-grained and fine-grained regions caused by two crystallization processes are also induced by hydrogen. Enhanced light absorptance is observed due to light trapping based on surface geometry changes of a-Si:H films, while the formation of a mixture of nanocrystalline silicon and remained a-Si:H after crystallization suggests that the overall material stability can potentially be increased. The relationship between crystallinity, fluence and number of pulses is also investigated. Furthermore, a step-by-step crystallization process is introduced to protect the hydrogen diffusing out in order to reduce the defect density, and the relationship between residue hydrogen concentration, fluence and step width is discussed. Finally, the combined effects show that the one-step process of surface texturing and step-by-step crystallization induced by excimer laser processing is very promising for a-Si:H thin film solar cell applications