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International Journal of Photoenergy
Volume 2013, Article ID 364638, 6 pages
http://dx.doi.org/10.1155/2013/364638
Research Article

The Effect of Bandgap Graded Absorber on the Performance of a-Si1–xGex:H Single-Junction Cells with μc-SiOx:H N-Type Layer

Department of Photonics, National Chiao Tung University, 1001 University Road, Hsinchu 300, Taiwan

Received 27 July 2013; Revised 24 October 2013; Accepted 28 October 2013

Academic Editor: Gaetano Di Marco

Copyright © 2013 Hung-Jung Hsu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We reported the effect of bandgap grading of absorbers on the performance of a-Si1−xGex:H cells employing μc-SiOx:H n-layer. The influence of bandgap grading widths extended from the p-layer (the p/i grading) and the n-layer (the i/n grading) to the absorber on the cell performance which were systematically studied. The p/i grading reduced the interface defects and thus improved the . The reduced and FF were presumably due to the degraded hole transport by the potential gradient of p/i grading. Increasing the i/n grading width improved the carrier collection significantly. The EQE, the , and the FF were improved substantially. Bias-dependent EQE revealed that the carrier collection is efficient in the cell employing optimal i/n grading. On the other hand, increasing the i/n grading width was accompanied by the decrease in long-wavelength response which potentially constrained the i/n grading width. Compared to the cell without grading, the a-Si1−xGex:H cells with optimal p/i and i/n grading width improved the efficiency from 5.5 to 7.5%.