Thin film amorphous and microcrystalline Si for solar cells

Electrical properties and stability of hydrogenated amorphous silicon (a-Si:H) are dominated by hydrogen movement in the film. Hydrogen movement and the Si film structures are affected by heat treatment. We have investigated the influence of anneal treatment on a-Si: H films. The a-Si: H was deposited on metal substrates. The structures investigated were i/n⁺/Mo, n/n⁺/Mo, p/p⁺/Mo, and PIN/n⁺ SS. Four types of thermal annealing were done; nitrogen atmosphere anneal, vaccum anneal, rapid thermal anneal (RTA), and excimer laser anneal. The anneal temperature ranged from 100 to 1200°C. Dark and light I-V studies show an improvement in short-circuit current and open-circuit voltage with a low temperature anneal (200-300°C). Raman scattering spectroscopy examination showed that microcrystallization initiated even at a low temperature of 600°C. It was found that the anneal time only has a small effect on crystallization but that the anneal temperature has a critical effect. The micro-crystalline silicon exhibited improved photo response after rf plasma hydrogen passivation of grain boundaries.