Metastability in hydrogenated nanocrystalline silicon solar cells
- PDF / 266,099 Bytes
- 10 Pages / 585 x 783 pts Page_size
- 25 Downloads / 236 Views
Metastability in hydrogenated nanocrystalline silicon solar cells Guozhen Yue,a) Baojie Yan, Gautam Ganguly, Jeffrey Yang, and Subhendu Guha United Solar Ovonic LLC, Troy, Michigan 48084 (Received 18 October 2006; accepted 1 February 2007)
Light-induced metastability in hydrogenated nanocrystalline silicon (nc-Si:H) single-junction solar cells was studied systematically. First, we observed no light-induced degradation when the photon energy was lower than the band gap of the amorphous phase; degradation occurred when the energy was higher than the band gap in the amorphous phase. The light-induced degradation could be annealed away at an elevated temperature. We concluded that the light-induced defect generation occurred mainly in the amorphous phase. Second, forward current injection did not degrade the nc-Si:H cell performance. However, a reverse bias during light soaking enhanced the degradation. Third, the nc-Si:H cells made with an optimized hydrogen dilution profile showed minimal degradation although these cells had a high amorphous volume fraction. This indicated that the amorphous volume fraction was not the only factor determining the degradation. Other factors also played important roles in the nc-Si:H stability.
I. INTRODUCTION
Light-induced defect generation in hydrogenated amorphous silicon (a-Si:H) due to the Staebler–Wronski effect1 has been a subject of intense study because it degrades the performance of a-Si:H-based solar cells. Although significant effort has been made toward understanding the mechanism and reducing the amount of light-induced degradation, it remains as an unresolved issue. It is believed that the defect creation is caused by recombination of the excess electron-hole pairs generated by photo-excitation or forward-bias current injection. Applying a reverse bias to a cell during lightsoaking reduces the recombination probability of the electron-hole pairs and thus reduces the degradation in a-Si:H based solar cells. In recent years, hydrogenated nanocrystalline silicon (nc-Si:H) has attracted remarkable attention due to its ability to absorb long wavelength photons and its better stability under prolonged light soaking. nc-Si:H is an
a)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as the Outstanding Meeting Paper for the 2006 MRS Spring Meeting Symposium A Proceedings, Vol. 910. DOI: 10.1557/JMR.2007.0144 1128 J. Mater. Res., Vol. 22, No. 5, May 2007 http://journals.cambridge.org Downloaded: 17 Mar 2015
inhomogeneous material composed of an amorphous phase, crystalline grains, and grain boundaries with a wide range of crystalline volume fraction. It also exhibits preferential orientation, and an anisotropic transport may be expected. Its metastability behavior, therefore, shows a substantial complexity and controversy, even more than its a-Si:H counterpart. Previously, it was reported that no light-induced degradation is observed in nc-Si:H cells.2,3 Recently, it was found that certain nc-Si:H cells show light-induced degradat
Data Loading...
