Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are studied for use as the emitter in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. Low interface recombination velocity and high open-circuit voltage are achieved by a low substrate temperature (<150°C) intrinsic a-Si:H deposition which ensures immediate amorphous silicon deposition. This is followed by deposition of n-type a-Si:H at a higher temperature (>200°C) which improves dopant activation and other properties. A prolonged atomic H pretreatment to clean the c-Si surface is actually detrimental because it creates additional defects in the c-Si lattice. However, a brief H pretreatment is beneficial and may render the intrinsic interlayer unnecessary. The n-type a-Si:H thickness must be limited to ~5 nm to minimize current loss, because the phosphorous doped a-Si:H layer has significant absorption in the usable solar spectrum. Using the optimized a-Si:H emitter, we obtain efficiency of nearly 17% on planar float-zone (FZ) silicon and 15% on planar Czochralski (CZ) silicon substrates with aluminum back-surface-field (Al-BSF) and contacts.
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The authors are indebted to Dr. Ajeet Rohatgi and Dr. Vijay Yelundur at Georgia Institute of Technology for providing the FZ-Si substrates with screen-printed Al-BSF used in the experiments. We also thank NREL colleagues Russell Bauer, Charles Teplin, Scott Ward, Anna Duda, Richard Crandall, and Pauls Stradins for valuable technical assistance and helpful discussion. This work is supported by the U.S. DOE under Contract #DE-AC36-99G010337.
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Wang, T., Iwaniczko, E., Page, M. et al. High-Performance Amorphous Silicon Emitter for Crystalline Silicon Solar Cells. MRS Online Proceedings Library 862, 235 (2004). https://doi.org/10.1557/PROC-862-A23.5