Journal of the Korea Institute of Information and Communication Engineering (한국정보통신학회논문지)

The Korea Institute of Information and Commucation Engineering (한국정보통신학회)
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A study on the capacitance-voltage characteristics of the CdZnS/CdTe heterojunction

CdZnS/CdTe 이종접합의 커패시턴스-전압 특성에 관한 연구

  • Received : 2011.05.11
  • Accepted : 2011.05.16
  • Published : 2011.06.30
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Abstract

In this work, we fabricated the CdZnS/CdTe heterojunction and investigated the C-V characteristics to determine the depletion width and the charge density distribution. A parallel experiment on CdS/CdTe heterojunction was also carried out for comparison. The depletion region width, for CdZnS/CdTe heterojunction, was nearly constant, regardless of bias voltage. However, the depletion region was wider than that of CdS/CdTe heterojunction due to high resistivity of CdZnS film. The interface charge density of CdZnS/CdTe heterojunction was increased linearly with the bias voltage and showed lower values than those for CdS/CdTe junction. The open circuit voltage of CdZnS/CdTe heterojunction solar cells increased with zinc mole ratio due to reducing of the electron affinity difference between CdZnS and CdTe films. However, the increase of series resistance due to the high resistivity of Cd1-xZnxS films results in reducing conversion efficiency.

본 연구에서는 CdZnS와 CdTe로 구성되는 이종접합 소자를 제작하고 커패시턴스-전압 특성을 조사하였다. CdS/CdTe 접합의 경우, 역방향 바이어스가 증가함에 따라 공핍층의 폭이 커져 커패시턴스 값이 약간 감소하였으나 CdZnS/CdTe 접합에서는 CdTe 박막 내에서의 공핍층 폭이 바이어스에 크게 영향을 받지 않아 커패시턴스 값이 역방향 바이어스에 따라 거의 변화가 없었다. 바이어스 전압을 인가하지 않은 상태에서의 공핍층 폭은 높은 CdZnS 박막의 비저항 및 낮은 캐리어 농도로 인해 CdS/CdTe 접합보다 CdZnS/CdTe 접합에서 보다 큰 값을 나타내었다. CdZnS/CdTe 태양전지의 개방전압은 Zn의 비율이 커짐에 따라 CdZnS 박막과 CdTe 박막의 전자 친화력 차이의 감소로 인하여 크게 증가하였으나, Zn 비율이 0.35 이상인 경우 오히려 감소함을 알 수 있었다. 또한 CdZnS 박막의 높은 비저항이 태양전지의 직렬저항을 상승시켜 전지의 변환 효율은 오히려 감소함을 알 수 있었다.

Keywords

References

  1. Ting L. Chu and Shirley S. Chu, "Recent Progress in Thin-Film Cadmium Telluride Solar Cells", Progress in photovoltaics research and application, vol. 1, pp.31-42, 1993, https://doi.org/10.1002/pip.4670010105
  2. G. H. Bauer, "Thin Film Solar Cell Materials", Applied Surface Science, vol. 70/71, pp.650-659, 1993. https://doi.org/10.1016/0169-4332(93)90596-4
  3. K. W. Mitchell, A. L. Fahrenbruch, and R. H. Bube, "Photovoltaic determination of optical‐absorption coefficient in CdTe", J. Appl. Phys., vol. 48, pp.829-830, 1977. https://doi.org/10.1063/1.323636
  4. Wu, X., Keane, J.C., Dhere, R.G., DeHart, C., Albin, D.S., Duda, A., Gessert, T.A., Asher, S., Levi, D.H., Sheldon P., "16.5%-Efficient CdS/CdTe polycrystalline thin-film solar cell", In: Proceedings of the 17th European Photovoltaic Solar Energy Conf., Munich, Germany, vol. II, pp. 995, 2001.
  5. Repins, M.A. Contreras, B. Egaas, C. DeHart, J. Schart, C.L. Perkins, B. To and R. Noufi, "Accelerated Publication 19.9%-efficient ZnO/CdS/ CuInGaSe2 solar cell with 81.2% fill factor", Prog. Photovolics, vol. 16, pp. 235-239, 2008. https://doi.org/10.1002/pip.822
  6. Jae-Hyeong Lee, Woo-Chang Song, Jun-Sin Yi, Kea-Joon Yang, Wun-Dong Han, Joon Hwang, "Growth and properties of the Cd1-xZnxS thin films for solar cell applications", Thin Solid Films, vol. 431-432, pp.349-353, 2003. https://doi.org/10.1016/S0040-6090(03)00526-1
  7. A. L. Fahrenbruch, V. Vasilchenko, F. Buch, K. Mitchell, and R. H. Bube, "II-VI photovoltaic heterojunctions for solar energy conversion", Appl. Phys. Lett., vol. 25, no. 10, pp.605-608, 1974. https://doi.org/10.1063/1.1655329
  8. R. A. Mickelsen, W. S. Chen, Y. R. Hsiao, and V. E. Lowe, "Polycrystalline Thin-Film CuInSe2/CdZnS Solar Cells", IEEE Trans. Electron Devices, vol. ED-31, no. 5, pp.542-546, 1984.
  9. A. R. Riben and. D. L. Feucht, "nGe-pGaAs heterojunctions,". Solid State Electron., vol. 9, pp. 1055-1065, 1966 https://doi.org/10.1016/0038-1101(66)90129-8
  10. F.L. Castillo-Alvarado, J.A. Inoue-Chavez, O. Vigil-Galan, E. Sanchez-Meza, E. Lopez-Chavez, G. Contreras-Puente, "C-V calculations in CdS/CdTe thin films solar cells", Thin Solid Films, vol. 518, pp.1796-1798, 2010. https://doi.org/10.1016/j.tsf.2009.09.035
  11. K. L. Chopra and S. R. Das, Thin Film Solar Cells, Plenum Press, New York, Chap. 4, 1983.
  12. H. D. Kim, "Preparation and photovoltaic properties of sintered CdS/CdTe solar cells with TCO films", Ph. D. thesis, Kaist, 1995.