Fabrication of thin-film polycrystalline silicon solar cells by silane-gas-free process using aluminum-induced crystallization

The authors have proposed a silane-gas-free fabrication process for thin-film polycrystalline Si solar cells. The process includes formation of a polycrystalline Si seed layer by aluminum-induced crystallization (AIC), crystallization of a Si film formed by physical vapor deposition (PVD) techniques for a base layer, aluminum diffusion from the AIC-grown Si (AIC-Si) layer to the base layer and pn-junction formation by the spin-on-glass technique. The crystal grains grew to a size of similar to20 mum in diameter through crystallization of the electron-beam-evaporated Si film on the AIC-Si layer, and the carrier lifetime was about 0.6 mus. In the solar cell fabricated by this process, the AIC-Si layer acts as a back-surface-field (BSF) layer, and the energy band is also inclined in its base layer so that the minority carriers can be pushed back to the depletion layer. These features indicate the possibility of fabricating low-cost and high-efficiency thin-film polycrystalline Si solar cells. The issues that must be pursued to realize high efficiency are reduction of oxygen atom inclusions during Si film deposition, passivation of the grain boundaries and development of a deposition technique for Si films having intermediate packing densities between those of electron-beam-evaporated films and sputter-deposited films, to prevent crack formation when the Si films are crystallized.