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TECHNOLOGYSOLAR


Figure 7. I-V characteristics of the 23.0% efficiency HIT solar cell


and 8. Since we achieved a 22.8% conversion efficiency with a 98-µm silicon substrate, we have been continuously trying to fabricate HIT solar cells with much thinner silicon substrates [4, 5]. As for mechanical strength, no solar cell warping has yet been seen down to a 58-µm substrate. Figure 9 shows the behavior of the normalized Isc and Voc of HIT solar cells over substrate thickness. As we predicted with a simulation, the Voc of the HIT solar cell increases at least down to a 58-µmthick silicon substrate. We actually achieved a very high Voc of 747 mV with a 58-µm substrate. On the other hand, the Isc decreases more rapidly than the Voc increases. To recover this transmission loss of Jsc with a thinner silicon substrate, the design of a strong optical confinement structure is urgently required.


Conclusion In this paper, we described Sanyo’s recent activities for improving the power generating performance and reducing the production cost of HIT solar cells. We have continuously been developing the passivation capability of a-Si/c-Si heterointerfaces, the transparency of the TCO and so on to raise the conversion efficiency. As a result, we achieved a conversion efficiency record of 23.0% with a cell area of 100.4 cm2


.


In addition, utilizing the benefits of a highly symmetrical structure and low SRV, we demonstrated a conversion efficiency of 22.8% with a cell thickness and area of 98 µm and 100.3 cm2, respectively. We also briefly mentioned other institutions’ results on heterojunction solar cells. A number of institutions have been studying the fundamental characteristics of the a-Si/c-Si heterojunction. The integration of Sanyo and other institutions’ studies is expected to bring fruitful improvements to a-Si/c-Si heterojunction solar cells.


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Figure 8. I-V characteristics of the 22.8% efficiency HIT solar cell with 98-µm thickness


Figure 9. Behaviour of parameters for HIT solar cells with a silicon substrate thinner than 100 µm. Values are normalized by that of a solar cell with a 96-µm-thick substrate.


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REFERENCES [1] Sanyo Electric Co., Ltd., News Release, May 22, 2009. (HIT is a trademark of SANYO Electric Co., Ltd.) [2] M. Taguchi, Y. Tsunomura, H. Inoue, S. Taira, T. Nakashima, T. Baba, H. Sakata, and E. Maruyama, Proc. 24th EUPVSEC, 21-25 September 2009, Hamburg Germany, pp. 1690-1693. [3] H. Sakata, T. Nakai, T. Baba, M. Taguchi, S. Tsuge, K. Uchihashi, and S. Kiyama, 28th IEEE PVSC(2000). pp. 7-12. [4] D. Fujishima, H. Inoue, Y. Tsunomura, T. Asaumi, S. Taira, T. Kinoshita, M. Taguchi, H. Sakata, and E. Maruyama, 35th IEEE PVSC, 20-25 June 2010, Honolulu, Hawaii (to be published). [5] H. Inoue, Y. Tsunomura, D. Fujishima, A. Yano, S. Taira, Y. Ishikawa, T. Nishiwaki, T. Nakashima, T. Asaumi, M. Taguchi, H. Sakata, and E. Maruyama, Proc. 2009 MRS Fall Meeting (to be published). [6] M. Schmidt, L. Korte, A. Laades, R. Stangl, Ch. Schubert, H. Angermann, E. Conrad, and K.v. Maydell, Thin Solid Films 515 (2007), pp. 7475– 7480. [6] M. Schmidt, L. Korte, A. Laades, R. Stangl, Ch. Schubert, H. Angermann, E. Conrad, and K.v. Maydell, Thin Solid Films 515 (2007), pp. 7475– 7480. [7] H. Angermann, L. Korte, J. Rappich, E. Conrad, I. Sieber, M. Schmidt, K. Hübener, and J. Hauschild, Thin Solid Films 516 (2008), pp. 6775–6781. [8] Mario Tucci, Luca Serenelli, Enrico Salza1, Luisa Pirozzi, Giampiero de Cesare, Domenico Caputo, Matteo Ceccarelli, Pierino Martufi, Simona De Iuliis, Lambert J. Geerligs, 23rd European Photovoltaic Solar Energy Conference, 1-5 September 2008, Valencia, Spain


www.solar-pv-management.com Issue IX 2010


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