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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/6936

Title: 利用硝酸處理與雙層抗反射膜研製改善矽晶太陽能電池效能
The Study and Fabrication of Crystalline Silicon Solar-Cell Efficiencies Improved by HNO3 Treatment and Double-layer
Authors: Yung-An Lu
Contributors: NTOU:Department of Electrical Engineering
Keywords: 電漿輔助化學氣相沉積(PECVD);雙層抗反射膜;氮化矽;硝酸處理;轉換效率;環境測試
Plasma enhanced chemical vapor deposition (PECVD);Double-layer anti-reflection coating;Silicon nitride;Nitric acid treatment;Conversion efficiency;Environmental test
Date: 2009
Issue Date: 2011-06-22T09:02:07Z
Abstract: 目前國內外太陽能產業發展研究製程技術,皆是針對如何提高效率進行改進,同時亦必須考量到成本之降低。本論文研究之太陽電池的製程,是使用Plasma Enhanced Chemical Vapor Deposition (PECVD),在晶片上鍍製的抗反射層鍍膜Anti-reflection Coating (ARC)。PECVD沉積溫度為450℃,作用氣體為甲烷(silane,SiH4) 和氨氣(ammonia,NH3),經調整兩種作用氣體流量及其混合比例可以決定抗反射層鍍膜的折射係數(n)。這結果可決定鍍膜的組成,吾人經公式計算並設計出三組雙層抗反射膜DL1(n1=1.91、n2=2.05、d1=70nm、d2=53nm)、DL2(n1=1.91、n2=2.17、d1=70nm、d2=51nm)及DL3(n1=1.91、n2=2.26、d1=70nm、d2=49nm)和單層抗反射膜SL(n1=2.05、d1=100nm)的鍍製條件。在調整氣體流量比改變折射係數之實驗中,得知單層抗反射與雙層抗反射膜所需之折射係數與氣體流量比在n=1.91時為75、n=2.05時為8.1、n=2.17時為5、n=2.26時為4。太陽電池的光照面鍍製雙層抗反射層,是用來減少入射陽光的反射,提升轉換效率。從紫外光譜儀量測結果得知,雙層抗反射膜之反射率在1%以下之波段範圍較寬,導致反射率下降,增加入射光,能達成提升轉換效率效果。單晶矽鍍製單層抗反射膜與雙層抗反射膜之轉換效率分別為16.74%與17.09%。多晶矽方面鍍製單層抗反射膜與雙層抗反射膜之轉換效率分別為15.46%與15.57%。如以量子效率量測結果對應至反射率上,在短波長與長波長部份,可以發現反射量減少而增加入射光,會使得量子效率獲得改善。 為進一步提升轉換效率,本論文利用硝酸處理方式浸泡太陽能電池。在太陽能電池表面會因磷擴散造成雜質濃度必須消除,其主要目的為減少表面載子複合速率,增加載子壽命,提高轉換效率。實驗結果顯示最佳條件為浸泡兩次硝酸,每次浸泡時期間為五分鐘。從SIMS量測結果顯示,經過硝酸浸泡處理過後的太陽能電池,近表面濃度明顯下降,從量子效率之短波長部份可觀察出來。單晶矽太陽能電池未經硝酸處理與經硝酸處理的轉換效率分別為16.74%和17.34%,明顯提升0.6%。多晶矽太陽能電池未經硝酸處理與經硝酸處理的轉換效率分別為15.46%和15.66%,提升0.2%。如果太陽電池直接擴散71Ω/□之整體轉換效率並不會比經硝酸處理後還來的佳,因此可以得知硝酸處理之步驟對於轉換效率的提升有一定的作用。量子效率量測結果顯示,表面雜質濃度下降,會使表面之複合率下降,而導出更多的電子,吾人可從短波長能明顯的觀察出來。 在製作完太陽能電池後,為驗證太陽能電池對環境的容忍度,本論文對電池進行鹽水浸泡與燒烤環境測試。經過兩天之鹽水浸泡後,發現電極因氧化的關係使轉換效率大幅降低。燒烤測試溫度分別以50℃與100℃測試,轉換效率並沒有太大的影響。主要因素是為太陽能電池燒結製程溫度為700℃~750℃高溫,其燒結溫度遠高於燒烤測試溫度,因此燒烤之測試對太陽能電池效率影響不大。
Photovoltaic technology permits the transformation of solar light directly into electricity. The cell design and manufacturing process for the high efficiency crystalline silicon solar cells were finalized and their characteristics were qualified. A good anti-reflective coating (ARC) is vital for solar cell performance as it ensures a high photocurrent by minimal reflectance. In this thesis simulated and experimented single (SL) and double layer (DL) antireflective coatings based on the refractive index and conversion efficiency are presented. PC1D solar cell simulations show that an increase in short circuit current density of 36.61mA/cm2 was possible by replacing an optimized single layer with the abovementioned double layer. A different approach is to implement a SiO2/SiN stack deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD).PECVD deposition temperature at 450℃, allows for tuning refractive index (n) of deposit films by adjusting deposition parameters, where the most used is the gas flow ratio of the precursor gases. Anti-reflective layer has been deposited with n varying from 1.91 to 2.17 using a ammonia/silane gas mixture. Three sets of double-layer anti-reflection coating DL1(n1=1.91, n2=2.05, d1=70nm, d2=53nm), DL2(n1=1.91, n2=2.17, d1=70nm, d2=51nm), and DL3(n1=1.91, n2=2.26, d1=70nm, d2=49nm) and single-layer anti-reflection coating SL(n1=2.05, d1=100nm) were calculated through function. In addition, through the experiment where the refractive index (n) was altered by adjusting the gas flow, the ratio between the needed refractive index (n) for the single-layer and double-layer anti-reflection coatings and the gas flow was 75 for 1.91, 8.1 for 2.05, 5 for 2.17, and 4 for 2.26. Deposited double-layer anti-reflection coating can have enhanced incident light and accordingly enhanced conversion efficiency when the reflectivity on the surface is decreased. The reflectance spectra were used ultraviolet spectrometer measure to compare the effect on the short circuit current density, JSC, for single and double-layer anti-reflection coating solar cells which were both based on the low cost material silicon solar cell. The efficiency of single-crystal silicon (sc-Si) anti-reflection coating was 16.74% and that of double-layer anti-reflection coating was enhanced to 17.09% while that of multi-crystalline silicon (mc-Si) single-layer anti-reflection coating was 15.46% and enhanced to 15.57% for double-layer anti-reflection coating. For the reduced reflectivity of the double-layer anti-reflection coating, it improves the short and long wavelength regime performance of efficiency especially in the former. On the other hand, in this research, nitric acid was used to lower the concentration of n layer resulting from phosphorus diffusion reduce the recombination rate of surface carriers and increase the lifetime of the carriers to further enhance the conversion efficiency. Results showed that the optimal condition was when samples immersed into nitric acid twice and 5min each time. The SIMS measurements shown that after the nitric acid treatment, the concentration near the surface lowered significantly and it could be observed by the short wavelength of quantum efficiency. The improvement effect was obvious sc-Si solar cell without and with nitric acid treatment, the conversion efficiency was enhanced from 16.74% to 17.34% and the mc-Si solar cell enhanced from 15.46% to 15.66%, respectively. The experiment result shown that the overall conversion efficiency of direct diffusion of 71Ω/□ did not appear to be better than with nitric acid treatment, indicating that nitric acid treatment had a limited effect on the enhancement of the conversion efficiency. As far as the quantum efficiency is concerned, due to the reduction in the concentration of foreign substances on the surface which decrease recombination rate on the surface, more electrons were induced and it could be easily observed by the long wavelengths. In thesis we perform many environmental tests, such as heating and soaking in salt water. We use 50℃and 100℃ heating sc-Si and mc-Si which are heating from 1 to 8 hours. Because the firing temperature of the solar cell (700℃~750℃) was far higher than the temperature used during the heating test, it did not have much influence on the efficiency. It obvious the variation of conversion efficiency that solar cells soaked in salt water from 1 to 2 days, in which the solar cells electrodes are oxidation by salt. Compared with the different heating test parameters, thin solar cells which are obtained by firing process have no (conversion efficiency) lose after being heated, but soaking in salt water solar cells which are decrease evidently. Environmental tests show that our designed solar cells have more durable.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M96530035
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