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, R C. Reedy, E Iwaniczko, Q Wang, B P. Nelson, Y Xu, Alan Gallagher, H M. Branz, J Crandall, J Yang, S Guha
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.
Journal of the Materials Research Society
a-Si:H, n-i-p, out-diffusion, solar cells
, Reedy, R.
, Iwaniczko, E.
, Wang, Q.
, Nelson, B.
, Xu, Y.
, Gallagher, A.
, Branz, H.
, Crandall, J.
, Yang, J.
and Guha, S.
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 February 24, 2024)