研究生: |
謝瑞益 Hsieh, Jui-Yi |
---|---|
論文名稱: |
玻璃基板上利用PECVD金屬誘發橫向結晶(MILC)低溫成長非晶矽/奈米矽/二氧化鈦薄膜太陽能電池之研究 A Study of α-Si:H/nc-Si/TiO2 Thin Film Solar Cell with PECVD Metal Induced Lateral Crystallization (MILC) Technology |
指導教授: |
蔡宗祐
Tsai, Tzong-Yow 方炎坤 Fang, Yean-Kuen |
學位類別: |
碩士 Master |
系所名稱: |
電機資訊學院 - 微電子工程研究所 Institute of Microelectronics |
論文出版年: | 2009 |
畢業學年度: | 97 |
語文別: | 中文 |
論文頁數: | 102 |
中文關鍵詞: | 太陽電池 、金屬銹發橫向結晶 |
外文關鍵詞: | solar cell, MILC |
相關次數: | 點閱:66 下載:2 |
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傳統PN或PIN結構之非晶矽太陽能電池,容易造成光線直接穿透及P/I接面處容易出現大量的電子電洞對復合,而導致轉換效率降低。針對此缺點,本論文提出一種新穎的太陽能電池結構:TiO2/nc-Si/α-Si:H/ITO/glass來克服。本結構利用金屬(金)誘發橫向結晶(Metal Induced Lateral Crystallization, MILC)技術在玻璃基板上銹發成長奈米矽薄膜,再利用奈米矽薄膜有較高的載子移動率及其表面的粗糙化(texture)結構,來增加光線在元件內行徑的次數,以提高光子在主動層內被吸收的機率。此外,利用二氧化鈦薄膜(TiO2)可吸收UV光的特性,來提高元件對太陽光的吸收頻譜範圍;並以其高能隙(Eg>3.5eV)的特性來降低電子電洞對複合的機會,以提升轉換效率。
首先,吾人採用電漿助長化學氣相沈積系統(PECVD)在ITO玻璃上成長氫化非晶矽薄膜,且在400℃溫度下,以金屬銹發橫向結晶技術(MILC)結晶出奈米矽薄膜。接著使用射頻磁控式電漿鍍膜法成長二氧化鈦薄膜,最後使用蒸著法鍍上指叉狀鋁金屬作為電極,如此完成整個元件的製作。
本研究採用場發射掃描式電子顯微鏡(FE-SEM)、原子力顯微鏡(AFM)、拉曼光譜儀(Raman Spectroscopy)、歐傑電子光譜儀(AES)、傅立葉光譜儀(FTIR)、光譜儀(Spectra Pro-500)等儀器來分析各層薄膜結構及光電特性,並利用HP4145B量測各層不同薄膜厚度對電流增益、Jsc、Voc、Fill Factor、efficiency等重要參數的影響。
吾人比較TiO2/nc-Si/α-Si:H/ITO/glass及nc-Si/α-Si:H/ITO/glass不同結構光/暗電流,結果發現加入二氧化鈦的確可使光/暗電流增益從原先的1.5倍變成61.2倍。如此證實了TiO2的功用。最後利用TiO2/nc-Si/α-Si:H/ITO/glass結構成長出太陽電池元件,經過標準光源AM1.5(100mW/cm2)照射後所量測出來其初步特性為:Voc=0.8V、Isc=4.52mA、FF=0.59、η=2.13%。吾人相信,如再最佳化上層之指叉狀金屬電極,一定可再提高轉換效率至4~5%以上。
In the traditional solar cell with PN or PIN structures, the light is easy to pass through these devices. There are many recombinations of electron-hole pair at the P/I interface, thus it reduced the conversion efficiency. Therefore, a new structure of TiO2/nc-Si/α-Si:H/ITO/glass was developed to overcome the shortage. The thesis used metal (Au) induced lateral crystallization (MILC) of hydrogenated amorphous silicon (α-Si:H) thin film to obtain nanocrystalline Si thin film (nc-Si) on the glass substrate. The nc-Si thin film possesses higher carrier mobility and texture structure on the surface. Scattering of injected photons happened at these textured interfaces to enhance the absorption photons in the active layer, and thus it increased the conversion efficiency. The solar absorption spectrum extended from visible to UV range because the TiO2 material. The TiO2 can reduce the recombination probability of electron-hole pair for its large energy gap (Eg>3.5eV), so that it can further promote conversion efficiency.
First, the PECVD method was employed to deposit the α-Si:H film on the ITO glass substrate. The nc-Si films were obtained by the MILC method below 400℃. Next, the radio-frequency sputtering system was used to deposit TiO2 film on the nc-Si film. The Al electrode of finger type was finally obtained by the evaporation. The physical and photoelectric properties of the nc-Si and TiO2 films were measured by FE-SEM, AFM, Raman Spectroscopy, AES, FTIR, and Spectra Pro-500. In addition, HP4145B was employed for measuring current gain, Jsc, Voc, Fill Factor and efficiency.
Furthermore, the photo/dark current ratios of the device structures with and without TiO2 layer on the top of nc-Si films were measured. The current gain could be promoted from 1.5 to 61.2 with the TiO2. Thus it verified to the extension of the solar absorption spectrum to the UV range, and the reduction of recombination probability of electron-hole pair of TiO2 function.
Finally, the initial performance of the new structure solar cell was measured with AM1.5(100mW/cm2). The initial properties are: conversion efficiency =2.13%, Isc=4.52mA, Voc=0.8V, and FF =0.59. It is expected that the conversion efficiency of 4~5% can be achieved by optimizing the contact electrode.
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