Texturization and rounded process of silicon wafers for heterojunction with intrinsic thin-layer solar cells

Abstract

Heterojunction with intrinsic thin-layer (HIT) solar cells are sensitive to interface state density. Traditional texture process for silicon solar cells is not suitable for HIT one. Thus, sodium hydroxide (NaOH), isopropanol (IPA) and mixed additive were tentatively introduced for the texturization of HIT solar cells in this study. Then, a mixture including nitric acid (HNO₃), hydrofluoric acid (HF) and glacial acetic acid (CH₃COOH) was employed to round pyramid structure. The morphology of textured surface and the influence of etching time on surface reflectance were studied, and the relationship between etching time and surface reflectance, vertex angle of pyramid structure was analyzed. It was found that the mixture consisting of 1.1 wt% NaOH, 3 vol% IPA and 0.3 vol% additives with etching time of 22.5 min is the best for HIT solar cells under the condition of 80°C. Uniform pyramid structure was observed and the base width of pyramid was about 2–4 µm. The average surface reflectance was 11.68%. Finally the effect of different processes on the performance of HIT solar cells was investigated. It was shown that these texturization and rounding techniques used in this study can increase short circuit current (J_sc), but they have little influence on fill factor (FF) and open circuit voltage (V_oc) of HIT solar cells.

Keywords

texturization / reflectance / pyramid / heterojunction with intrinsic thin-layer (HIT) solar cells

References

[1] Green M A. Solar Cells : Operating Principles, Technology and System Applications. New Jersey: Prentice-Hall Inc., 1982

[2] De Wolf S, Descoeudres A, Holman Z C, Ballif C. High-efficiency silicon heterojunction solar cells: a review. Green, 2012, 2(1): 7–24

[3] Fuhs W, Niemann K, Stuke J. Heterojunctions of amorphous silicon and silicon single crystals. In: Proceedings of AIP Conference, New York: AIP Publishing, 1974, 20: 345–350

[4] Taguchi M, Tanaka M, Matsuyama T, Tsuda S, Nakano S, Kishi Y, Kuwano Y. Improvement of the conversion efficiency of polycrystalline silicon thin film solar cell. In: Proceedings of Technical Digest of the 5th International Photovoltaic Science and Engineering Conference, Kyoto: International PVSEC. 1990, 689–692

[5] Taguchi M, Yano A, Tohoda S, Matsuyama K, Nakamura Y, Nishiwaki T, Fujita K, Maruyama E. 24.7% record efficiency HIT solar cell on thin silicon wafer. IEEE Journal of Photovoltaics, 2013, PP(99): 1–4

[6] Barrio R, González N, Cárabe J, Gandía J J. Optimisation of NaOH texturisation process of silicon wafers for heterojunction solar-cells applications. Solar Energy, 2012, 86(3): 845–854

[7] Tian J T, Feng S M, Wang K X, Xu H T, Yang S Q, Liu F, Huang J H, Pei Y. The influence of new additive in alkaline solution on the shape of pyramid on the monocrystal Si surface. Acta Physica Sinica, 2012, 61(6): 066803-1–066803-5 (in Chinese)

[8] Kashkoush I, Chen G, Nemeth D. Characterization of C-Si texturization in wet KOH/IPA and its effect on cell efficiency. In: Proceedings of 26th European Photovoltaic Solar Energy Conference and Exhibition. Hamburg: EU PVSEC, 2011, 2020–2023

[9] Gangopadhyay U, Kim K H, Dhungel S K, Manna U, Basu P K, Banerjee M, Saha H, Yi J. A novel low cost texturization method for large area commercial mono-crystalline silicon solar cells. Solar Energy Materials and Solar Cells, 2006, 90(20): 3557–3567

[10] Yang Z P, Yang Y, Li X D, Xu Y, Wang W J. Effect of sodium silicate on texture of single crystalline silicon wafer for solar cell. Journal of the Chinese Ceramic Society, 2005, 33(12): 1472–1476 (in Chinese)

[11] Fan Y J, Han P D, Liang P, Xing Y P, Ye Z, Hu S X. Differences in etching characteristics of TMAH and KOH on preparing inverted pyramids for silicon solar cells. Applied Surface Science, 2013, 264(1): 761–766

[12] Montesdeoca-Santana A, Jiménez-Rodríguez E, González-Díaz B, Borchert D, Guerrero-Lemus R. Ultra-low concentration Na₂CO₃/NaHCO₃ solution for texturization of crystalline silicon solar cells. Progress in Photovoltaics: Research and Applications, 2012, 20(2): 191–196

[13] Chen G, Kashkoush I. Effect of pre-cleaning on texturization of c-Si wafers in a KOH/IPA mixture. ECS Transactions, 2010, 25(15): 3–10

[14] Gosálvez M A, Nieminen R M. Surface morphology during anisotropic wet chemical etching of crystalline silicon. New Journal of Physics, 2003, 5(1): 100-1–100-28

[15] Fesquet L, Olibet S, Damon-Lacoste J, De Wolf S, Hessler-Wyser A, Monachon C, Ballif C. Modification of textured silicon wafer surface morphology for fabrication of heterojunction solar cell with open circuit voltage over 700 mV. In: Proceedings of 34th IEEE Photovoltaic Specialists Conference. Philadelphia: IEEE, 2009, 754–758

[16] Damon-Lacoste J, Cabarrocas P R. Toward a better physical understanding of a-Si:H/c-Si heterojunction solar cells. Journal of Applied Physics, 2009, 105(6): 063712-1–063712-7

[17] Sopori B L, Pryor R A. Optical characteristics of textured /100/ oriented silicon surfaces–application to solar cells. In: Proceedings of 15th IEEE Photovoltaic Specialist Conference. Kissimmee: IEEE, 1981, 466–472

[18] Palik E D, Bermudez V M, Glembocki O J. Ellipsometric study of orientation-dependent etching of silicon in apueous KOH. ECS Transactions, 1985, 132(4): 871–884

[19] Hua X S, Zhang Y J, Wang H W. The effect of texture unit shape on silicon surface on the absorption properties. Solar Energy Materials and Solar Cells, 2010, 94(2): 258–262

[20] Park H, Kwon S, Lee J S, Lim H J, Yoon S, Kim D. Improvement on surface texturing of single crystalline silicon for solar cells by saw-damage etching using an acidic solution. Solar Energy Materials and Solar Cells, 2009, 93(10): 1773–1778

[21] Kovacs G T A, Maluf N I, Petersen K E. Bulk micromachining of silicon. Proceedings of the IEEE, 1998, 86(8): 1536–1551

[22] Kulkarni M S, Erk H F. Acid-based etching of silicon wafers: mass-transfer and kinetic effects. Journal of the Electrochemical Society, 2000, 147(1): 176–188

[23] Park H, Lee J S, Kwon S, Yoon S, Kim D. Effect of surface morphology on screen printed solar cells. Current Applied Physics, 2010, 10(1): 113–118

Acknowledgements

This work was supported by Ministry of Education of China (No. 62501040202) and the Special Fund for the Development of Strategic Emerging Industries of Shenzhen, China (No. JCYJ20120831110939098). We thank all members of the thin films group at the Photonics and Information System Integration Institute and Hisunpv Technology Co., Ltd for their support of this work and helpful discussion. We also acknowledge the Analytical and Testing Center of Huazhong University of Science and Technology for SEM spectra measurements and Wuhan National Laboratory for Optoelectronics for the reflectance spectra measurement.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg