High-rate deposition of a-Si:H thin layers for high-performance silicon heterojunction solar cells

In this paper, we describe a technique for high-quality interface passivation of n-type crystalline silicon wafers through the growth of hydrogenated amorphous Si (a-Si:H) thin layers using conventional plasma-enhanced chemical vapor deposition. We investigated the onset of crystallization of the a-Si:H layers at various deposition rates and its effect on the surface passivation properties. Epitaxial growth occurred, even at a low substrate temperature of 90 degrees C, when the deposition rate was as low as 0 center dot 5 angstrom/s; amorphous growth occurred at temperatures up to 150 degrees C at a higher deposition rate of 4 center dot 2 angstrom/s. After optimizing the intrinsic a-Si:H layer deposition conditions and then subjecting the sample to post-annealing treatment, we achieved a very low surface recombination velocity (7 center dot 6cm/s) for a double-sided intrinsic a-Si:H coating on an n-type crystalline silicon wafer. Under the optimized conditions, we achieved an untextured heterojunction cell efficiency of 16 center dot 7%, with a high open-circuit voltage (694mV) on an n-type float-zone Si substrate. On a textured wafer, the cell efficiency was further enhanced to 19 center dot 6%. Copyright (c) 2011 John Wiley & Sons, Ltd.