Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/8682
標題: 氫化非晶碳化矽超晶格薄膜太陽電池
a-SiCx:H/a-SiCy:H Superlattices Thin Film Solar Cells
作者: 張嘉洲
Chang, Chia-Chou
關鍵字: silicon quantum dot;矽量子點;superlattice,silicon thin film solar cell;超晶格;矽薄膜太陽電池
出版社: 電機工程學系所
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摘要: 
改善矽薄膜太陽電池轉換效率的有效方法,是調整矽薄膜太陽電池吸光層的能隙值製作疊層太陽電池,以增加太陽光譜吸收範圍。採用a-SiCx:H /a-SiCy:H 超晶格結構,可以由富矽子層厚度控制矽量子點形成的大小,由量子點的量子尺寸效應達成較大彈性調整能隙值的目的。
氫化非晶碳化矽薄膜及太陽電池是以13.56 MHz電漿增強化學氣相沉積系統製作。氫化非晶碳化矽薄膜製做方法主要是調變甲烷對矽烷比例( R = CH4/SiH4+CH4 ) 從30% 至95%,藉由週期性組合不同矽碳鍵結配比,以製作不同能隙值及不同緻密程度的薄膜。
當矽烷對甲烷比例從30% 變化至95%,a-Si1-xCx:H薄膜中的碳分量x從0.037上升至0.497。a-Si1-xCx:H薄膜的光學常數以橢圓偏光儀量測而得,隨著甲烷對矽烷比例升高,介電係數實部ε1與虛部ε2對應之鋒值位置往高的光子能量方向移動,而峰值強度則會下降。薄膜的能隙值提高,而折射率則會下降。上述的結果顯示薄膜中含有較多的碳,隨著碳含量的增加,使得薄膜的折射率下降,薄膜緻密性不佳。
改變甲烷對矽烷比例從R = 30% 、R = 45% 至R = 60% 製作不同碳含量比例的子層其厚度為10 Å,並以矽奈米微粒層為另一子層其厚度為50 Å,總週期數為50的nc-Si:H/a-Si1-xCx:H超晶格薄膜太陽電池。太陽電池實驗結果顯示,當R值增加即a-Si1-xCx:H子層的碳含量增加時,由於薄膜內缺陷密度增加使得太陽電池的效率、填充因子以及開路電壓會下降。因此在較低碳含量( R = 30% ) 的太陽電池具有較好的初始效率為3.98% 。改以a-Si:H薄膜作為子層所製作的a-Si:H (10 Å) / a-Si1-xCx:H (50 Å) 超晶格薄膜太陽電池,因a-Si:H子層品質良好,可以提高短路電流密度至11.12 mA/cm2,太陽電池效率可以提高至5.12%。

Stacking different energy gaps of silicon thin-film solar cells to form tandem solar cells can extend the absorption of solar spectrum for improving energy transfer efficiency. Using a-SiCx:H/a-SiCy:H superlattices structure can easily control the size of Si quantum dots formation in the Si-rich sublayers . Thus, the energy gap of the superlattice can be widely adjusted by changing the Si quantum dot size and the sublayer thickness.
All samples are deposited by 13.56 MHz plasma enhanced chemical vapor deposition (PECVD). The a-Si1-xCx:H films are fabricated by changing gas flow ratios of methane and silane (R = CH4/SiH4+CH4) from 30% to 95%. The variation of the energy gap and the density of a-SiCx:H or a-SiCy:H films can be well modified by periodical spatial distribution of various Si-C bonds of different sublayers.
By changing R ratio increasing from 30% to 95%, the carbon content x of a-Si1-xCx films increases form 0.037 to 0.497. The peak position of the real and the imaginary part of the dielectric constants of the a-Si1-xCx:H films were measured by spectroscopic ellipsometry, which are shifted to the higher energy and the peak height is increased. The results indicate that increasing the carbon contents reduce the film density and increase the degree of disorder.
The nc-Si:H/a-Si1-xCx:H superlattices thin film solar cells with 1-nm-thickness nc-Si:H sublayers and 5-nm-thickness a-Si1-xCx:H sublayers, which the carbon atoms ratio are controlled by changing R ratio from 30% to 60%. The increasing carbon atoms ratio in a-Si1-xCx:H sublayers reduces the values of energy transfer efficiency (η), fill factor (FF) and open-circuit voltage (Voc)¬ of the solar cells. The solar cell deposited with low R (= 30%) has the better performance which the η is about 3.98%. Using a-Si:H films as the sublayers, an a-Si:H (10 Å)/a-Si1-xCx:H (50 Å) superlattices solar cell was fabricated. Due to the low defect density of a-Si:H sublayers, the short-circuit current density can be increased to 11.2 mA/cm2 and the η is increased to about 5.12 %.
URI: http://hdl.handle.net/11455/8682
其他識別: U0005-2708200908043200
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