| Summary: | 博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 100 === For current status of global solar energy, the photovoltaic world market is dominated by crystalline silicon solar cells which account for nearly 90% of world PV cell and module production. Thin film solar cells are believed to be candidates for significant production volume in the future because of their potential to reach the very low cost target of 〈US$ 1/watt. Silicon is an abundant material. Thus, low cost silicon thin-film solar cells have a good chance of gaining a significant market share. However, a significant increase in efficiency improvement is a crucial and key task for silicon thin film solar cells in the near future.
In order to improve the efficiency, we use several technologies to effectively improve the optical properties and electrical performance for the thin film solar cells. By inserting a thin p-type hydrogenated microcrystalline silicon (p-μc-Si:H) layer between transparent conductive oxide (TCO) and p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) layer, the photovoltaic performances of amorphous silicon solar cells can be improved due to reduction of the surface potential barrier. The results show that higher efficiency can be produced by incorporating the p-μc-Si:H layer into the solar cell so as to improve the open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF). Besides, we study the effects of deposition temperatures and electrode distances in the i-a-Si:H layer of a-Si:H solar cells with regard to enhanced the Jsc and thereby conversion efficiency. It is demonstrated that the absorption coefficient in an i-a-Si:H layer can be increased to provide higher Jsc under fixed thickness. Results show that the optimized parameters improve the Jsc of a-Si:H solar cells from 16.06 to 16.52 mA/cm2, yielding an excellent conversion efficiency of 10.86%.
Furthermore, an anti-reflection (AR) layer has been fabricated and applied in micromorph tandem (a-Si:H/μc-Si:H) solar cells. The porous AR layers are produced on glass substrates by plasma enhanced chemical vapor deposition using a CF4 and O2 gas mixture. The tandem solar cells with the AR layer show the increased Jsc of the solar cells due to increased light transmittance from air/glass interface. With the AR layer, the Jsc of the tandem cell increases by 0.29 mA/cm2. Meanwhile, the solar cell efficiency increases from 11.15% to 11.55% (3.5% in relative) which allows us to develop more efficient a-Si:H based solar cells. Finally, this study has reported the development of a-Si:H/μc-Si:H solar cells with GZO/p-μc-Si:H structure, high absorption coefficient of top i-a-Si:H layer and AR layer. However, the Jsc_top must be raised at least 12.9 mA/cm2 for current matching in the tandem cells. By using high deposition temperature and electrode distance parameters when depositing the i-a-Si:H layer, a best-result solar cell achieved an excellent conversion efficiency = 13.17%, Voc = 1366 mV, Jsc = 13.1 mA/cm2 and FF = 0.736.
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