具正/背面奈米銦/銀粒子侷域性表面電漿子的單晶矽太陽能電池特性提升之研究

Performance of Plasmonics Thin Silicon Solar Cell Using In and Ag Nanoparticles on Front and Rear Side

廖俊欽(Chun-Chin Liao 廖俊欽)

指導教授 ： 何文章

國立臺北科技大學/機電學院/光電工程系所/碩士(2013年)

摘要

本論文是製作具正/背面奈米銦/銀粒子侷域性表面電漿子(Localized Surface Plasmon, LSP)的單晶矽太陽能電池及探討特性提升之研究。當太陽光入射至正/背面有表面電漿結構的矽太陽電池時，短波段的光會與正面的奈米銦粒子產生侷域性表面電漿子共振(Localized Surface Plasmon Resonance, LSPR)，增加光子轉換成光電流的轉換率；而長波段的光可與電池背面的奈米銀粒子產生侷域性表面電漿子共振，將長波段的光散射回矽半導體進行再次吸收；如此可增加太陽能電池總的輸出光電流，太陽能電池的轉換效率也隨光電流輸出增加而獲得的有效提升。
本論文先製作的裸矽太陽能電池，首先是在P型矽基板上以旋轉塗佈(Spin-On Film, SOF)的方式，在基板上旋塗一層磷擴散源後，放入快速熱退火爐形成n+- p二極體。其背面電極圖案設計為格子狀電極(Grid-Shape Electrode)，利用電子束蒸鍍機蒸鍍鋁(Al)後，再經由快速熱退火爐進行熱退火，使鋁與矽之間能形成良好的歐姆接觸；正面電極圖案設計為指叉狀電極圖案(Finger Electrode)，同樣利用電子束蒸鍍機蒸鍍鈦(Ti)/鋁(Al)，完成裸矽太陽電池(Bare Solar Cell)元件。
裸矽太陽能電池正面的表面電漿奈米結構製作，一開始先利用電子束蒸鍍二氧化鈦(TiO2)當作空間層(Space Layer)於太陽電池表面，本文分別鍍30 nm、59.5 nm 和85 nm三種不同厚度，之後放入在氫氣環境下以200 ℃，持溫30分鐘進行快速熱退火處理，使TiO2重新排列形成較緻密的空間層，然後再鍍3.8 nm銦薄膜於TiO2表面，最後試片放在氫氣環境下以200 ℃，持溫30分鐘進行快速熱退火處理形成奈米銦粒子。經過反射率(Reflectance)、外部量子效率量測(External Quantum Efficiency, EQE)和太陽光電I-V特性量測(AM1.5 I-V)，發現空間層厚度的增加，會讓正面的奈米銦粒子侷域性表面電漿共振波長紅移。本實驗獲得之結果，將3.8 nm的銦奈米粒子形成於30 nm、59.5 nm 和85 nm之TiO2上的太陽能電池，其銦奈米粒子表面電漿貢獻可使矽太陽能電池光電流密度輸出提升分別為8.29 % (25.09 mA/cm2 → 27.17 mA/cm2)、6.85 % (30.37 mA/cm2 → 32.45 mA/cm2)、3.86 % (29.01 mA/cm2 → 30.13 mA/cm2)；光電轉換效率提升分別為7.86 % (9.41 % →10.15 %)、6.35 % (12.12 % → 12.89 %)、5.56 % (11.51 % → 12.15 %)。我們可知在30 nm二氧化鈦及3.8 nm的銦奈米粒子條件下，其銦奈米粒子表面電漿貢獻對矽太陽能電池性能有較明顯的提升，其總光電流密度達27.17 mA/cm2及轉換效率達10.15 %。
最後，我們製作一背面具格子狀鋁電極(鋁遮蔽率 60 %)的裸矽太陽能電池，其背面用電子束蒸鍍30 nm的銀薄膜，並在氮氣環境下300 ℃，持溫3分鐘，退火形成奈米銀粒子。經量測結果，具背面銀奈米粒子時，因表面電漿貢獻，可使此矽太陽能電池光電流密度提升1.39 % (23.10 mA/cm2 → 23.42 mA/cm2)，轉換效率提升1.54 % (9.09 % → 9.23 %)。背面銀奈米粒子製作完成後，此矽太陽能電池的正面則蒸鍍一層30 nm的二氧化鈦及一層In 3.8 nm銦膜及退火，完成正/背面具銦/銀奈米粒子侷域性表面電漿子矽太陽能電池製作，正面銦奈米粒子表面電漿貢獻可使矽太陽能電池光電流密度提升8.51 % (27.25 mA/cm2 → 29.57 mA/cm2)，轉換效率提升9.78 % ( 10.74 % → 11.79 %)，其總光電流密度達29.57 mA/cm2及轉換效率達11.79 %。

關鍵字

單晶矽太陽能電池 ； 空間層 ； 侷域性表面電漿子 ； 銦和銀奈米粒子 ； 外部量子效率

並列摘要

In this work, the indium (In) and silver (Ag) nanoparticles forming on the front- and rear-side surface of thin silicon solar cell, respectively, to enhance photovoltaic performances due to plasmonics effects are reported. When the sunlight incident on the proposed solar cells, indium nanoparticles on the front surface can be enhanced the conversion rate of photons to photon-carriers at short wavelength band and the silver nanoparticles on the rear surface scattered the long-wavelength photons, which contributed by localized surface plasmon.

In this study, bare Si solar cell was first fabricated and characterized. The liquid phosphorus source was spun upon on a 200 um-thick P-type silicon substrate and capped with a SiO2 layer. Then heat treated by RTA at 900 oC which the phosphorus atoms can be diffused into p-silicon, forming a p-n junction. The rear side electrode was grid-shape pattern Al electrode (Al coverage of 60 %), deposited by e-beam evaporation and photolithograph processing. Subsequently,
Al electrode was annealed at 450 oC in N2 atmosphere for 5 min to make the better ohmic contact. Simililary, the front-side finger Ti/Al electrode was obtained by e-beam deposition and lift-off process.
Secondly, 30 nm, 59.5 nm and 85 nm-thick TiO2 space layer are deposited on the fabricated bare cells, respectively, by e-beam evaporation. Before indium film deposited on the TiO2 surface, the TiO2 space layer was annealed at 200 oC in H2 atmosphere for 30 minutes to form a high quality and high density TiO2 space layer. Then 3.8 nm-thick Indium (In) was deposited upon those TiO2 space layer and all samples subsequently annealed at 200 oC in H2 atmosphere for 30 min to obtain indium nanoparticles. The reflection spectrum, external quantum efficiency (EQE) response, and photovoltaic I-V were measure and compared as the cell with and without indium nanoparticles on the TiO2 layer. The results show that the plasmon resonance wavelength of indium nanoparticles was red-shifted as the thickness of TiO2 increase. Under AM1.5 illumunation, the enhancement of the short-circuit current density (Jsc) of the plasmonics solar cells with 30 nm, 59.5 nm and 85 nm-thick TiO2 space layer are 8.29 % (from 25.09 mA/cm2 to 27.17 mA/cm2), 6.85 % (from 30.37 mA/cm2 to 32.45 mA/cm2) and 3.86 % (from 29.01 mA/cm2 to 30.13 mA/cm2), respectively, compare to the cell only with corresponding TiO2 layer. Similiary, the conversion efficiency (η) can be achieved 7.86 % (from 9.41 % to 10.15 %), 6.35 % (from 12.12 % to 12.89 %) and 5.56 % (from 11.51 % to 12.15 %), respectively. Therefore, the plasmonic Si solar cell with indium nanoparticles on the 30 nm TiO2 space layer exhibited the best improving in photocurrent and conversion efficiency. Summary, the totally short-circuit current density output of 27.17 mA/cm2 and conversion efficiency of 10.15 % are obtained in the proposed cell with plasmonics on the front-side surface.

Finally, the bare Si solar cell with gride-shap pattern Al-electrode (coverage of 60%) on the rear-side was fabricated. Next, 30 nm-thick silver film was deposited on the rear-side surface and then annealed at 300 oC in N2 atmosphere for 3 min, forming Ag nanoparticles. The short-circuit current density increase of 1.39 % (from 23.10 mA/cm2 to 23.42 mA/cm2) and conversion efficiency increase of 1.54 % (from 9.09 % to 9.23 %) were obtained as the cell only with Ag nanoparticles on the rear-side surface. However, the cell of with metallic nanoparticles on both the front and rear surface, the photocurrent density increase of 8.51 % (from 27.25 mA/cm2 to 29.57 mA/cm2) and conversion efficiency enhanced by 9.78 % (from 10.74 % to 11.79 %) are presented. Therefore, the total short-circuit current density of 29.57 mA/cm2 and the conversion efficiency of 11.79 % were obtained as the thin silicon solar cell with In and Ag nanoparticles on the front and rear surface.

並列關鍵字

Single Crystal Silicon Solar Cell ； Space Layer ； Localized Surface Plasmon ； Indium and Silver Nanoparticle ； External Quantum Efficiency

參考文獻

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