Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/7285
標題: 以高壓空乏法製作氫化微晶矽薄膜太陽電池
Fabrication of hydrogenated microcrystalline silicon thin-film solar cells by high pressure depletion method
作者: 李季樺
Li, Chi-Hua
關鍵字: hydrogenated microcrystalline silicon;氫化微晶矽;solar cell;太陽電池
出版社: 電機工程學系所
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摘要: 
本論文使用40.68 MHz超高頻電漿增強化學氣相沉積系統,改變i層功率密度、沉積壓力及p層氣體摻雜比例製作氫化微晶矽(μc-Si:H)薄膜。藉由拉曼光譜儀、X光繞射儀、掃描式電子顯微鏡、電流-電壓量測儀及量子效率測量儀,分析太陽電池的結構及電學特性變化。
p型μc-Si:H薄膜以改變摻雜氣體比例 (B2H6 / SiH4 = 0.25%~1% )製作。由結果顯示當p層摻雜氣體比例為0.25%時,結晶比例高,易誘發後續i層薄膜析出結晶,孵化層較薄,相反的當p層為非晶矽結構,抑制i層析出結晶,p/i介面載子傳導不佳,使得太陽電池特性下降。適當的p型微晶矽結構有助於i層的結晶成長及品質改善。
固定p層摻雜氣體比例為0.5%,改變i層沉積壓力由3至7 torr製作的太陽電池之實驗結果顯示當沉積壓力上升時,結晶比例逐漸下降,由SEM剖面結構可看出低壓時柱狀結晶截面小,較多的柱狀結晶造成較多的晶核邊界,使載子復合,降低長波長區段之電流響應。升高壓力可減少晶核邊界缺陷,使電性獲得改善。
固定p層摻雜氣體比例為0.25%,改變i層沉積壓力5~8 torr製作太陽電池。壓力於5、6及7 torr 時太陽電池結晶結構呈現垂直柱狀,而沉積壓力增加至7.5 torr時孵化層變厚,結晶結構呈現倒圓錐狀,最後於8 torr時為全非晶矽結構。電流-電壓結果顯示當沉積壓力於5、6及7 torr時,具有高的電流密度為典型微晶相的特徵,壓力於7.5 torr時,薄膜結構為微晶轉非晶的混合相,電流密度介於中間值,為微晶與非晶混和相所造成之結果,而壓力為8 torr時,具有明顯低的電流密度,此為非晶相的特徵。壓力5 ~ 7.5 torr時之太陽電池具有一定比例的微晶矽結構,故具有較低的開路電壓約為0.45 V,沉積壓力為8 torr的太陽電池僅具有非晶矽結構,開路電壓明顯上升至0.84 V。這些結果指出,沉積壓力於7 ~ 7.5 torr為微晶至非晶轉介區,介於轉介區邊界的7 torr太陽電池有最佳的薄膜特性及轉換效率。良好的氫化微晶矽太陽電池必須控制在微晶轉非晶的轉介區邊界,一般發生在較高壓的條件。

In this thesis, 40.68 MHz very-high-frequency plasma-enhanced chemical vapor deposition is used to fabricate μc-Si:H thin-film solar cells with changing the i-layer power density, deposition pressure and doping gas flow ratio of p-layer. The structural and electrical properties of solar cells are investigated by Raman spectrometer, x-ray diffraction, scanning electron microscope, current-voltage measurement and quantum efficiency measurement.
P-type μc-Si:H thin films are fabricated by varying doping gas flow ratio of B2H6/SiH4 = 0.25%~1%. The results indicate that the ratio at 0.25% of p-layer has highest crystalline volume ratio (XC) which easy to induce the crystallization of i-layer so the incubation layer is thinner. On the contrary, the p-layer structure of amorphous phase suppresses the crystallization of i-layer, result in poor carrier conduction in p/i interface, and makes the solar cells properties deteriorate. Appropriate structure of microcrystalline P-type film can contribute to the growth and quality improvement of i-layer with microcrystalline phase.
For the doping gas flow ratio of p-layer fixed at 0.5%, a series of solar cells are fabricated by changing deposition pressure of i-layer from 3 to 7 torr. The results indicate that increasing pressure decrease the crystalline volume ratio of the cells. Low-pressure deposition induces many columnar crystals with small cross section. There are many grain boundaries to make carrier recombination which reducing current response in long wavelength region. High-pressure deposition can reduce the grain boundary defects, then the electrical properties of solar cells can be improved.

For the p-layer doping gas flow ratio fixed at 0.25%, a series of solar cells is fabricated by changing deposition pressure of i-layers from 5 to 8 torr. The results demonstrate that the solar cells are columnar structure for deposition pressure from 5 to 7 torr, further increasing the thickness of incubation layer the cone-shape crystalline structures are formed when pressure at 7.5 torr, and then the structure is whole amorphous phase for the 8 torr condition. Current-voltage measurement results show that the deposition pressure on the 5, 6 and 7 torr, the cells have the high current density which is typical characteristics of microcrystalline phase. The structure of 7.5-torr cell is mixed-phase of microcrystalline and amorphous phase that the current density has the middle value. The 8-torr cell is fully amorphous and has the lower current density which is the typical characteristic of amorphous phase. There have a certain percentage of microcrystalline phase for the solar cells deposited at 5 ~ 7.5 torr, therefore it has a lower open-circuit voltage of about 0.45 V. The open-circuit voltage of the amorphous phase of the 8-torr cell is increased to 0.84 V. These results illustrate that transition region from microcrystalline to amorphous occurred from 7 to 7.5 torr. The solar cell deposited at 7 torr is at boundary of transition region, and has the best performance and conversion efficiency. Good μc-Si:H solar cells must be fabricated at the boundary of transition region from microcrystalline to amorphous, which is generally controlled at high pressure condition.
URI: http://hdl.handle.net/11455/7285
其他識別: U0005-2908201110300600
Appears in Collections:電機工程學系所

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