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

在本論文中，我們以Atlas軟體建立新型矽基薄膜太陽電池模擬模組，並討論各種物理參數對於元件效率的影響。單接面的氫化非晶矽和氫化微晶矽太陽能電池皆以Atlas 模擬出其電學特性，之後再將非晶矽和微晶矽電池疊層構成的雙接面太陽能電池進行模擬。當改變底層太陽能電池吸收層的能隙以及電子能態中帶尾能態的分佈時，開路電壓 (Voc) 會隨著能隙增加而上升，短路電流 (Jsc) 則是在能隙小於1.4電子伏特後，開始下降。這是因為電子和電洞佔據在侷限能態 (localized state) 上是無法有效移動，造成短路電流 (Jsc) 的下降。除此之外，我們也利用射頻電漿輔助化學氣相沉積系統 (PECVD) 製作氫化微晶矽薄膜。對於氫化微晶矽薄膜太陽能電池而言，結晶率是相當重要的議題。實驗中以利用調變氫氣流量，電漿能量還有不同的基板進行對於控制結晶率的研究。

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.