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.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Basu P, Boreland M, Shanmugam V, Sarangi D (2012) Non-acidic isotropic etch- back method for silicon wafer solar cells, US Prov. Patent. No.61/644730
Basu P, Hameiri Z, Sarangi D, Cunnusamy J, Carmona E, Boreland M (2013a) 18.7% Efficient inline-diffused screen-printed silicon wafer solar cells with deep homogeneous emitter etch-back. Sol Energy Mater Sol Cells 117:412–420
Basu P, Sarangi D, Boreland M (2013b) Single-component damage-etch process for improved texturization of monocrystalline silicon wafer solar cells. IEEE JPV 3:1222–1228
Basu P, Law F, Vinodh S, Kumar A, Richter P, Bottari F, Hoex B (2015) 0.4% absolute efficiency increase for inline-diffused screen-printed multicrystalline silicon wafer solar cells by non-acidic deep emitter etch-back. Sol Energy Mater Sol Cells 137:193–201
Basu P, Li J, Shanmugam V, Khanna A (2016) Heavy phosphorous tube-diffusion and non acidic deep chemical etch-back assisted efficiency enhancement of industrial multicrystalline silicon wafer solar cells. RSC Adv 6:35928–35935
Book F, Braun S, Herguth A, Dastgheib-Shirazi A, Raabe B, Hahn G (2010) The etchback selective emitter technology and its application to multicrystalline silicon. In: Proceedings of 35th IEEE photovoltaic specialists conference (IEEE PVSC), Honolulu, pp 1309–1314
Dastgheib-Shirazi A, Haverkamp H, Raabe B, Book F, Hahn G (2008) Selective emitter for industrial solar cell production: a wet chemical approach using a single side diffusion process. In: Proceedings of 23rd European photovoltaic solar energy conference (EU PVSEC), Valencia, pp 1197–1199
Duttagupta S, Lin F, Shetty K, Aberle A, Hoex B (2013) Excellent boron emitter passivation for high-efficiency Si wafer solar cells using AlOx/SiNx dielectric stacks deposited in an industrial inline plasma reactor. Prog Photovolt Res Appl 21:760–764
Ebong A, Cooper I, Rounsaville B, Tate K, Rohatgi A, Bunkenburg B, Cathey J, Kim S, Ruf D (2010) High efficiency in-line diffused emitter (ILDE) solar cells on mono-crystalline CZ silicon. Prog Photovolt Res Appl 18:590–595
Gilles D, Schroter W, Bergholz W (1990) Impact of the electronic structure on the solubility and diffusion of 3d transition elements in silicon. Phys Rev B 41(9):5770–5782
Goetzberger A, Shockley W (1960) Metal precipitates in silicon p–n junctions. J Appl Phys 31:1821–1824
Grove A, Leistiko O, Sah C (1964) Redistribution of acceptor and donor impurities during thermal oxidation of silicon. J Appl Phys 35:2695–2701
Haverkamp H, Shirazi A, Raabe B, Book F, Hahn G (2008) Minimizing the electrical losses on the front side: development a selective emitter process from a single diffusion. In: Proceedings of 33rd IEEE photovoltaic specialists conference (IEEE PVSC), San Diego, pp 430–433
Hilali M (2005) Understanding and development of manufacturable screen-printed contacts on high sheet-resistance emitters for low-cost silicon solar cells. Georgia Institute of Technology, PhD Thesis
Kane D, Swanson R (1985) Measurement of the emitter saturation current by a contactless photoconductivity method. In: Proceedings of 18th IEEE photovoltaic specialists conference (IEEE PVSC), Las Vegas, pp 578–583
Khanna A, Basu P, Filipovic A, Shanmugam V, Schmiga C, Aberle A, Mueller T (2015) Influence of random pyramid surface texture on silver screen-printed contact formation for monocrystalline silicon wafer solar cells. Sol Energy Mater Sol Cells 132:589–596
Liang Z, Zeng F, Song H, Shen H (2013) Effect of porous Si and an etch-back process on the performance of a selective emitter solar cell. Sol Energy Mater Sol Cells 109:26–32
Raabe B, Book F, Dastgheib-Shirazi A, Hahn G (2010) The development of etch-back processes for industrial silicon solar cells. In: Proceedings 25th European photovoltaic solar energy conference (EU PVSEC), Valencia, pp 1174–1178
Rothhardt P, Keding R, Wolf A, Biro D (2013) Co-diffusion from solid sources for bifacial n-type solar cells. Phys Status Solidi (RRL) 7:623–626
Shabani M, Yamashita T, Morita E (2008) Study of gettering mechanisms in silicon: competitive gettering between phosphorus diffusion gettering and other gettering sites. Solid State Phenom 131–133:399–404
Song K, Kim B, Lee H, Lee Y, Park C, Balaji N, Ju M, Choi J, Yi J (2012) Selective emitter using a screen printed etch barrier in crystalline silicon solar cell. Nanoscale Res Lett 7:410–417
Stassen A, Koppes M, Komatsu Y, Weeber A, Hoogboom J, Oosterholt J, Ritmeijer S, Groenewoud L (2009) Further improvements in surface modification of mc silicon solar cells: comparison of different post-PSG cleans suitable for in-line emitters. In: Proc. 24th European photovoltaic solar energy conference (EU PVSEC), Hamburg, PP 1657–1659
Syre M, Karazhanov S, Olaisen B, Holt A, Svensson B (2011) Evaluation of possible mechanisms behind P gettering of iron. J Appl Phys 110:024912
Voyer C, Biro D, Wagner K, Benick J, Preu R (2006) Fabrication of textured solar cells using sprayed phosphoric acid as the dopant source for the in-line diffusion. In: Proceedings 21st European photovoltaic solar energy conference (EU PVSEC), Dresden, pp 1157–1160
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).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
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
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10098-017-1354-9