非晶矽 / 微晶矽 疊層薄膜太陽能電池之模擬與微晶矽結晶率之探討

Abstract

In this study, a detailed electrical-optical computer modeling, based on the Atlas software, was used to investigate the effect of bandgap (Eg) and tail state distribution of intrinsic microcrystalline silicon thin film on thin film silicon solar cells. Complete tandem solar cell which consists of an a-Si:H top cell and a μc-Si:H bottom cell solar cell were simulated. In this study the bandgap and tail state distribution of the bottom cell were varied. The acceptor and donor tail state distribution of i-layer was assumed to be broader as the Eg increases in the bottom cells. WTA and WTD are used to represent the characteristic energy for acceptor-like tail state distribution, and characteristic energy for the donor-like tail state distribution, respectively. The open circuit voltage (Voc) increased with increasing Eg, but the short circuit current (Jsc) decreases when Eg is lower than 1.4eV. The lower Eg made the Voc and efficiency decease sharply, although the Jsc was kept at high value. Comparing the highest (1.6 eV) and lowest Eg (1.1 eV), the former has a better performance. Therefore, the Eg of bottom cell should not be lower than 1.3eV to avoid the decline of efficiency. In the second part of this thesis, I have studied the control of crystallinity in the growth of μc-Si:H thin films during plasma-enhanced chemical vapor deposition (PECVD) process. The crystallinity of μc-Si:H film increases with increasing film thickness. Through modulating the H2 flow in the deposition process, the crystallinity could be controlled. Base on the experimental results, the initial deposition condition is crucial for further growth. Through altering the deposition conditions and modulating the hydrogen flow, uniform crystallinity of about 50% could be achieved.