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

Published

April 1, 1998

Author(s)

A. H. Mahan, R C. Reedy, E Iwaniczko, Q Wang, B P. Nelson, Y Xu, Alan Gallagher, H M. Branz, J Crandall, J Yang, S Guha

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 compansate' 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 out-diffusion 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 respectivediffusion 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 16 s, using the insights obtained in this study.

Citation

Journal of the Materials Research Society

Volume

507

Pub Type

Journals

Keywords

a-Si:H, n-i-p, out-diffusion, solar cells

Citation

Mahan, A. , Reedy, R. , Iwaniczko, E. , Wang, Q. , Nelson, B. , Xu, Y. , Gallagher, A. , Branz, H. , Crandall, J. , Yang, J. and Guha, S. (1998), H-Out-Diffusion and Device Performance In n-i-p Solar Cells Utilizing High Temperature Hot Wire a si: H i-Layers, Journal of the Materials Research Society (Accessed July 27, 2024)