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H Out-Diffusion and Device Performance in n-i-p Solar Cells Utilizing High Temperature Hot Wire a-Si:H i-Layers

  • A. H. Mahan (a1), R. C. Reedy (a1), E. Iwaniczko (a1), Q. Wang (a1), B. P. Nelson (a1), Y. Xu (a1), A. C. Gallagher (a2), H. M. Branz (a1), R. S. Crandall (a1), J. Yang (a3) and S. Guha (a3)...

Abstract

Hydrogen out-diffusion from the n/i interface region plays a major role in controlling the fill factor (FF) and resultant efficiency of n-i-p a-Si:H devices, with the i-layer deposited at high substrate temperatures by the hot wire technique. Modeling calculations show that a thin, highly defective layer at this interface, perhaps caused by significant H out-diffusion and incomplete lattice reconstruction, results in sharply lower device FF's due to the large voltage dropped across this defective layer. One approach to this problem is to introduce trace dopant tailing to ‘compensate’ these defects, but the resultant cells exhibit a poor red response. A second approach involves the addition of buffer layers designed to retard this out-diffusion. We find that an increased H content, either in the n-layer or a thin intrinsic low temperature buffer layer, does not significantly retard this out-diffusion, as observed by secondary ion mass spectrometry (SIMS) H profiles on devices. All these devices have a defect-rich i-layer region near the n/i interface and a poor device efficiency. However, if this low temperature buffer layer is thick enough, the outdiffusion is minimized, yielding nearly flat H profiles and a much improved device performance. We discuss this behavior in the context of the H chemical potentials and H diffusion coefficients in the high temperature, buffer, n-, and stainless steel (SS) substrate layers. The chemical potential differences between the layers control the direction of the H flow and the respective diffusion coefficients, which depend upon many factors such as the local electronic Fermi energy and the extent of the H depletion, determine the rate. Finally, we report a 9.8% initial active area device, fabricated at 16Å/s, using the insights obtained in this study.

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1) Mahan, A. H. and Vanecek, M., AlP Conf. Proc. 234, 211 (1991).
2) Wu, Y., Stephen, J. T., Han, D. X., Rutland, J. M., Crandall, R. S., and Mahan, A. H., Phys. Rev. Lett. 77, 2049 (1996).
3) Mahan, A. H., Williamson, D. L., and Furtak, T. E., MRS Symp. Proc. 467, 657 (1997).
4) Liu, X., White, B. E. Jr., Pohl, R. O., Iwaniczko, E., Jones, K. M., Mahan, A. H., Nelson, B. N., Crandall, R. S., and Veprek, S., Phys. Rev. Lett. 78, 4418 (1997).
5) Mahan, A. H., Carapella, J. C., and Gallagher, A. C., U.S. Patent 5,397,737 (1995).
6) Unold, T., Reedy, R. C. Jr., and Mahan, A. H., 17th ICAMS, Budapest, 1997, to appear in J. non-Cryst. Sol. (1998).
7) Mahan, A. H., Iwaniczko, E., Nelson, B. P., Reedy, R. C. Jr., Unold, T., Crandall, R. S., Guha, S., and Yang, J., AIP Conf. Proc. 394, 27 (1996).
8) Upon investigation, we found that wide variations in our gas purging procedure, from a weekend pump to a 5 min purge between the HW n- and I-W i-layer depositions, made little difference in either the SIMS P profiles or the device FF's, leading us to conclude that we had inadequate “burial” of the P on the chamber walls before the i-layer deposition, due to the geometry of the shutter used for device fabrication.
9) Kusian, W., Kruhler, W., and Bullemer, B., Proc. 19th IEEE PV Spec. Conf., 577 (1987).
10) Street, R. A., Phys Rev B, 43, 2454 (1991).
11) Carlson, D. E. and Magee, C. W., Appl. Phys. Lett. 33, 81 (1978).
12) Pemg, T.-P. and Altstetter, C. J., Acta. Metall. 34, 1771 (1986).
13) Beyer, W. and Zastrow, U., Proc. MRS Symp. 420, 497 (1996).
14) Yang, J., private communication.
15) Based upon optical pyrometer measurements, filament currents of 14A and 16A correspond to approximate filament temperatures of 1930°C and 2100°C respectively.
16) Bauer, S., Herbst, W., Schroeder, B., and Oechsner, H., Proc. 26th IEEE PV Spec. Conf., 719 (1997).
17) Jones, S. (private communication) reports an initial η of 10.6% for an a-Si:H device using the VHF-GD deposition technique, at deposition rates of Å/s.

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