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Silicon nanocrystals embedded amorphous silicon solar cells
|關鍵字:||silicon nanocrystals;矽奈米晶粒;a-Si:H;solar cell;pulse-wave modulation of RF power;Hydrogen dilution;氫化非晶矽;太陽電池;脈波調變射頻電漿;氫氣稀釋||出版社:||電機工程學系||摘要:||
本論文以矽奈米晶粒摻入氫化非晶矽薄膜太陽電池之方法來探討並改善非晶矽太陽電池的光照衰退現象。以脈波調變射頻功率(pulse-wave modulated RF power)及高氫氣稀釋(H2 dilution)兩種方式沉積矽奈米晶粒及控制其結晶程度。脈波調變射頻功率的電漿開關比為30 ms/10 ms，氫氣稀釋比R值(R = H2/SiH4) 則分別由 R = 4、31、50變化至80。由拉曼光譜(Raman Spectrum)、高解析度穿透式顯微鏡(HRTEM) 及原子力顯微鏡(AFM)分析結果顯示薄膜由R = 4的非晶結構逐漸的轉變成具有矽奈米晶粒的非晶薄膜(nc-Si:H)。在R = 50及R = 80條件下沉積之薄膜具有奈米晶粒其結晶大小分別約為3 nm及4 nm，結晶比例則分別約為31及59%。太陽電池的製作採用Glass/ITO/p/i/n/Al。本實驗將nc-Si:H (R = 80)與a-Si:H(R = 4)作為i層堆疊的雙層膜結構(薄膜厚度分別為100nm及300nm)，與i層為單一結構的a-Si:H作為比較(薄膜厚度400nm)。在AM1光照條件下進行96小時光照衰退電性量測，結果顯示i層為nc-Si:H/a-Si:H雙層膜結構之太陽電池其開路電壓、短路電流及轉換效率分別衰減為0.1%、23%及16%，而填充因子則增加9%。 i層為單一a-Si:H結構之參考太陽電池其開路電壓、短路電流、填充因子及轉換效率分別衰減約5%、38%、8%及45%。上述結果顯示nc-Si:H的加入使得開路電壓、短路電流、填充因子及轉換效率分別改善5%、15%、17%及29%。矽奈米晶粒摻入氫化非晶矽太陽電池具較低的光照衰退比例，可以明顯改善氫化非晶矽太陽電池的衰退現象，是值得發展的薄膜太陽電池。
In this thesis, silicon nanocrystals (nc-Si) embedded into a-Si:H solar cell were fabricated to investigate and improve the photodegradation properties of a-Si:H solar cells. Pulse-wave modulated RF power and high hydrogen dilution were used to control the crystallinity of nc-Si in a-Si:H films. The plasma on/off ratio of pulse-wave modulated RF power was fixed to 30 ms/10 ms. Hydrogen dilution ratio R (R = H2/SiH4) was varied with R = 4, 31, 50 to 80.
Raman spectrum, high resolution transmission electron microscopy and atomic force microscopy measurements indicate that the grain size and crystallinity of the films are changed gradually from amorphous state (R = 4 sample) to nanocrystal structure. For R ratio increasing to R=50 and R = 80, the formation of nc-Si in the films was observed, and the size and the crystal volume ratio of the nc-Si is increased from 3 nm to 4 nm, and from 31% to 59%, respectively.
The structure of solar cell is Glass/ITO/p/i/n/Al mode. The i layer of the compared samples was fabricated by a single a-Si:H(Thickness is 400nm) film with R=4, and the i layer of the experimental samples was fabricated by the nc-Si:H(100nm)/a-Si:H (300nm)bi-layer stacked structure with R=80/R=4.
The I-V measurements on photodegradation under the conduction of AM1. After light-soaked 96 hours, The measurement indicates at bi-layer i layer sample, the values of open-circuit voltage (VOC), short-circuit current density (JSC), and conversion efficiency (η) which were decreased to 0.1%, 23%, and 16%, respectively; but fill factor (F.F.) was increased to 9%. Besides, at single i layer samples, the values of open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (F.F.), and conversion efficiency (η) were decreased about 5%, 38%, 8% and 45%, respectively.
As a result, the embedment of nc-Si:H was able to improve the values of open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (F.F.), and conversion efficiency (η) to 5%, 15%, 17%, and 29%. The solar cell with the silicon nanocrystals (nc-Si) embedded into a-Si:H thin film has lower photodegradation ratio. The degradation effect of the a-Si:H solar cell is improved obviously, the new design of solar cell is worthy of development thereof.
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