Low degradation and fast annealing effects of amorphous silicon multilayer processed through alternate hydrogen dilution

Abstract

Alternately hydrogen diluted a-Si:H multilayers are shown to be a promising concept for the fabrication of stable a-Si:H solar cells or other a-Si:H based devices. The alternately hydrogen diluted amorphous silicon multilayers were obtained by toggling both the H2/SiH4 dilution ratio and the total flow rate of the gases under continuous UV light irradiation into the reaction chamber of a photochemical vapor deposition system. The films were characterized by Fourier transformed infrared spectroscopy, spectroscopic ellipsometry, cross-sectional transmission electron microscopy, and atomic force microscopy. We applied these multilayers as the active layer of p–i–n type thin film solar cells. The multilayer solar cells are compared to solar cells incorporating a-Si:H made from pure SiH4 gas and to solar cells incorporating a-Si:H made at a constant hydrogen dilution ratio containing nearly the same hydrogen amount as the multilayer. We report on the light-soaking and annealing behavior of the solar cells. The multilayer solar cell has an exceptionally high recovery rate at low temperatures, which makes the solar cell degradation behavior highly sensitive to the cell temperature during degradation. Following the relation, DH∝1/τ, where DH and τ are the diffusion coefficient for hydrogen and time constant for annealing, respectively, the layered structure in the multilayer possibly elevates DH, which accounts for rapid stabilization and annealing.