開發寬能隙氫化非晶矽氧薄膜應用於單接面及雙接面非晶矽薄膜太陽能電池

Abstract

本論文為開發寬能隙氫化非晶矽氧之材料並應用於矽基薄膜太陽能電池。在本研究中，氫化非晶矽氧薄膜與太陽能電池藉由電漿輔助化學氣相沉積技術製作而成。開發氫化非晶矽氧材料可為兩大部分。第一部分為開發未摻雜氫化非晶矽氧薄膜之研究。此部分將會藉由二氧化碳當作氧原子來源氣體，因此氧原子可以進入薄膜中。而在薄膜中的氧擴大了材料的能隙，但使光電導隨之減少，其可歸因於缺陷增多而導致電導降低。為解決膜中缺陷隨氧含量的提升而增加，可藉由改變基板溫度以及氫流量比以獲得較好的薄膜品質。將優化後的薄膜做為吸收層應用於非晶矽氧單接面電池，其在250 nm吸收層之厚度可獲得轉換效率為4.92%、開路電壓為910 mV、短路電流為8.55 mA/cm2及一填充因子為63.25%。此外，我們將氧加入n型氫化非晶矽薄膜中，增加其能隙，預期減少摻雜層之吸收損失，其結果顯示，相較於n型非晶矽，短路電流可提升至9.60 mA/cm2。而第二部分，將會藉由乙硼烷當作提供硼原子的來源氣體，使硼原子可以進入膜中，進而使得活化能降低，進而提升太陽能電池之內建電場。此外，並發現藉由改變氫流量比可獲得最佳非晶薄膜品質。最佳化後的p型非晶矽氧薄膜特性為能隙2.28 eV，活化能0.64 eV，電導為6.35×10-7 S/cm。將優化後的p型非晶矽氧薄膜應用於氫化非晶矽單接面電池之視窗層，以期減少摻雜層之光損失。相較於氫流量比為2.7的p型非晶矽氧，氫流量比為150的p型非晶矽氧應用於氫化非晶矽電池中之視窗層有較高的轉換效率，其轉換效率為6.65%、開路電壓為0.89 V、短路電流為13.57 mA/cm2、填充因子為55%。接著藉由加入一層p型非晶矽碳層於p/b介面以期減少接面缺陷而幫助載子傳輸及提升填充因子。優化後的p型非晶矽氧及p型非晶矽碳雙層結構做為窗戶層於氫化非晶矽電池中，其視窗層厚度分別為6 nm與8 nm，轉換效率為7.37%、開路電壓為0.89 V、短路電流為13.73 mA/cm2、填充因子為60.24%。最後，將優化後的p型和n型非晶矽氧層應用於非晶矽/非晶矽鍺雙接面太陽能電池之上電池中，預期減少摻雜層之吸收損失，使入射光有效的被利用進而轉換成光電流。其結果顯示，使用摻雜非晶矽氧層於上電池中，總電流提升從18.34至18.63 mA/cm2，，轉換效率提升從8.19%到8.90%，其中開路電壓提升從1.55到1.57V，短路電流提升從8.21到8.38 mA/cm2，填充因子提升從64.4到67.7%。此結果顯示，將寬能隙氫化非晶矽氧做為摻雜層應用於非晶矽/非晶矽鍺雙接面太陽能電池之上電池中，能有效減少吸收損失並提高太陽能電池之轉換效率。

The wide-bandgap hydrogenated amorphous silicon suboxide (a-SiOx:H) for amorphous silicon-based solar cell application has been investigated. The silicon-based solar cells was deposited by plasma-enhanced chemical vapor deposition (PECVD) technique. First of all, the undoped a-SiOx:H layer was studied. By adding CO2 as the source gas, the oxygen atoms can be incorporated into the film. The oxygen incorporation widened the bandgap so that wide-bandgap material was obtained, but reduced the photo conductivity which can be referred to the increase in defects in the film. We further adjusted the substrate temperature and hydrogen dilution for high-quality a-SiOx:H absorber. Application of the optimized a-SiOx:H absorber obtained the cell efficiency of 4.92% with the VOC of 910 mV, the JSC 8.55 mA/cm2 and the FF of 63.25%. Besides, employment of a-SiOx:H(n) in a-SiOx:H single-junction solar cell enhanced the JSC to 9.60 mA/cm2. As compared to the a-Si:H cell with a-SiOx:H(p) deposited at H2-to-SiH4 flow ratio of 2.7, the a-Si:H cell with a-SiOx:H(p) deposited at H2-to-SiH4 flow ratio of 150 had higher efficiency. In addition, the double p-layers were needed to reduced interface defect. Employment of 6-nm-thick a-SiOx:H(p)/ 8-nm-thick a-SiCx:H(p) as window layer in a-Si:H single-junction solar cell enhanced the cell efficiency to 7.37% with the JSC of 13.73 mA/cm2, the FF of 60.24 and VOC of 0.89 V. Finally, in a-Si:H/a-Si1-xGex:H tandem cell employment of the 6-nm-thick a-SiOx:H(p)/ 8-nm-thick a-SiCx:H(p) and a-SiOx:H(n) as window layer and n-layer of top cell enhanced the cell efficiency from 8.19 to 8.90% by increasing the JSC from 8.21 to 8.38, the FF from 64.37 to 67.68 and the VOC from 1.55 to 1.57 eV. Besides, the total JEQE was increased from 18.34 to 18.63 mA/cm2, which revealed that employment of wide-bandgap a-SiOx:H(p) and a-SiOx:H(n) in top cell reduced absorption loss in doped layer.