High Efficiency Amorphous and Microcrystalline Silicon Based Double-Junction Solar Cells Made with Very-High-Frequency Glow Discharge

70290 The microcrystalline silicon (mc-Si) solar cell is a potential candidate for substituting the amorphous silicon-germanium (a-SiGe) alloy bottom cell in the amorphous silicon (a-Si) alloy based multijunction solar cell. The advantages include no light-induced degradation and no expensive GeH4 source gas. However, the deposition rate of the intrinsic mc-Si layer must be increased (since a thicker mc-Si film is required compared to a-SiGe material) without affecting the material quality. In this project, a modified, very-high-frequency (MVHF) glow discharge process will be used to deposit high efficiency, small-area a-Si/mc-Si double-junction solar cells at high deposition rates. Then, the technology will be scaled up to fabricate a-Si/mc-Si double-junction cells in a roll-to-roll production pilot plant. Phase I will: (1) optimize the MVHF glow discharge parameters to deposit mc-Si intrinsic layers at high deposition rate of 10-15 ¿/s for solar cell application, (2) optimize deposition parameters for double-junction a-Si/mc-Si cells in order to obtain high cell efficiency and superior light stability, and (3) develop the hardware technology to deposit a-Si and mc-Si films over a large area 14¿x28¿ with good uniformity using the MVHF process. Commercial Applications and Other Benefits as described by the awardee: A commercially viable technology for the deposition of mc-Si film-based solar cells at a high deposition rate should lead to superior stable solar cell efficiency that in turn will result in higher rated commercial products. The superior stable efficiency of the product coupled with cost savings from eliminating GeH4 as a process gas should have a significant impact on the $/Watt value that would be passed on to the customer.