Abstract
A way of achieving lightly doped emitter is a combination of a heavy emitter diffusion and emitter etch back, which has an added advantage of phosphorous diffusion gettering. However, this chemical emitter etch-back process must fulfil some critical requirements, e.g. cost-effectiveness, near-conformal Si etching even after deep emitter etch back, controlled Si etch rate, post-etch clean Si surface and lowest safety issues in chemical handling and drainage. In this work, we report a new low-cost (less than 1 US Cents/wafer), single-chemical, non-acidic, high-throughput emitter etch-back process for tube-diffused emitters for crystalline Si wafers. This process uses only sodium hypochlorite solution at 80 °C as the Si etchant. This process is versatile with its applications on phosphorous and boron tube-diffused monocrystalline Si and phosphorous tube-diffused multicrystalline Si wafers. The preparation, usage and drainage of this highly diluted solution are easy and safe. The Si etching process leads to excellent spatial uniformity over large-area Si wafers (243 cm2). With deep etch back resulting in a change of sheet resistance by ~60 Ω/sq, the standard deviation value changes by only 2.7%. High surface conformity in the etch-back surface is evident from reflectance studies. Quasi-steady-state photoconductance and photoluminescence imaging are used to demonstrate improved electrical parameters of the etch-back wafers.
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Acknowledgements
The authors thank their colleagues from the Silicon Materials and Cells Cluster of the Solar Energy Research Institute of Singapore (SERIS) for their assistance in sample processing. SERIS is sponsored by the National University of Singapore (NUS) and Singapore’s National Research Foundation (NRF) through the Singapore Economic Development Board (EDB). The corresponding author also thanks Ministry of New and Renewable Energy (MNRE), Government of India for his funding for his research at National Centre for Photovoltaic Research and Education (NCPRE).
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Basu, P.K., Khanna, A. A new single-component low-cost emitter etch-back process for silicon wafer solar cells. Clean Techn Environ Policy 19, 1655–1665 (2017). https://doi.org/10.1007/s10098-017-1354-9
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DOI: https://doi.org/10.1007/s10098-017-1354-9