Improvement of Single-Junction a-Si:H Thin-Film Solar Cells Toward 10% Efficiency
- PDF / 210,915 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 43 Downloads / 166 Views
Improvement of Single-Junction a-Si:H Thin-Film Solar Cells Toward 10% Efficiency P. H. Cheng, S. W. Liang, Y. P. Lin, H. J. Hsu, C. H. Hsu and C. C. Tsai National Chiao Tung University, Hsinchu, Taiwan
ABSTRACT The hydrogenated amorphous silicon (a-Si:H) single-junction thin-film solar cells were fabricated on SnO2:F-coated glasses by plasma-enhanced chemical vapor deposition (PECVD) system. The boron-doped amorphous silicon carbide (a-SiC:H) was served as the window layer (p-layer) and the undoped a-SiC:H was used as a buffer layer (b-layer). The optimization of the p/b/i/n thin-films in a-Si:H solar cells have been carried out and discussed. Considering the effects of light absorption, electron-hole extraction and light-induced degradation, the thicknesses of p, b, n and i layers have been optimized. The optimal a-Si:H thin-film solar cell having an efficiency of 9.46% was achieved, with VOC=906 mV, JSC=14.42 mA/cm2 and FF=72.36%.
INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) is one of the promising materials for thin-film solar cell applications [1]. The large bandgap and the high absorption coefficient make it suited for single- and multi- junction solar cells. The undoped layer (i-layer) in the a-Si:H thin-film solar cell is the key element to generate photo-current. However, the a-Si:H suffers certain degree of light-induced degradation (also known as Staebler-Wronski effect, SWE [2,3]) which leads to a reduction in efficiency. The degree of degradation can be reduced by the consideration of the absorber thickness and the film quality (e.g. microstructure parameter or conductivity).The dependence of the absorber thickness on efficiency is a trade-off between optical absorption and photo-generated carrier collection. Moreover, the doped layer (n-layer, p-layer) in the a-Si:H thin-film solar cell should consider not only the electrical properties but also the optical influences. The boron-doped amorphous silicon carbide (a-SiC:H) has been served as the window layer (p-layer) for its wider bandgap and reasonable conductivity [4]. The thickness of the window layer should be minimized to reduce optical losses while keeping sufficient built-in field for carrier extraction [5, 6]. The band offset between p-layer (~2.0 eV) and i-layer (~1.75 eV), however, induces defects at the p/i interface [7]. This defective heterojunction acts as a recombination center which limits the performance of the cells due to recombination losses [8]. A high quality buffer layer has therefore been inserted to alleviate the bandgap difference as well as the defects between p/i interfaces. In this study, experiments were carried out to improve the undoped a-Si:H and the doped aSiC:H. Effect of the thicknesses of the p/i/n layers were also investigated to optimized the cell performance. Efforts were integrated to achieve a high efficiency solar cell.
39
EXPERIMENT In this work, a-Si:H solar cells were fabricated by the radio frequency (27.12 MHz) plasma-enhanced chemical vapor deposition (PECVD) system. It is a commercial load-lo
Data Loading...
