應用於矽薄膜太陽能電池之高能隙及高導電率n型微晶矽氧化物作為背反射層的開發與研究

Abstract

本研究主要開發矽薄膜太陽能電池之高能隙及高導電率n型微晶矽氧化物作為背反射層。薄膜太陽能電池是由27.12 MHz的電漿輔助化學氣相沉積系統所製作。一般作為背反射層的條件為低折射率以及可接受的電導率，為了符合這些條件，我們改變二氧化碳與矽烷的比值、氫氣與矽烷加上氫氣的比值、沉積時的電漿功率以及腔體壓力來調整n型微晶矽氧化物中的氧含量。此外，我們將優化過的n型微晶矽氧化物應用在單層微晶矽太陽能電池上，並與不同的背反射結構做比較。在實驗中可以發現使用n型微晶矽氧化物取代原本的n型微晶矽與透明氧化導電層作為背反射結構在長波長有較高的量子效率，使用此種結構同時簡化了製程並達到較高的效率。將此種結構應用於多接面的太陽能電池，也有相同的效果。使用優化過後的n型微晶矽氧化物，可以達到雙接面太陽能電池最佳轉換效率為10.63 %，開路電壓為1.36 V、短路電流為10.36 mA/cm2以及填充因子為75.18 %，而三接面太陽能電池可以達到轉換效率為8.93 %，開路電壓為1.98 V、短路電流為6.31 mA/cm2以及填充因子為71.52 %。

In this thesis, large bandgap and highly conductive N-type μc-SiOX as the back reflecting (BR) layer for silicon (Si) thin-film solar cells has been investigated. The Si thin-film solar cells were prepared by the 27.12 MHz radio-frequency plasma-enhanced chemical vapor deposition (PECVD) system. The requirements of μc-SiOX:H(n) as the BR layer was low refractive index and acceptable conductivity. To meet the requirements of a back reflecting layer, the methods to adjust the oxygen content of μc-SiOX:H(n) such as varying CO2-to-SiH4 flow ratio, H2 dilution, RF power and pressure of PECVD process were executed. We also applied the optimized μc-SiOX:H(n) to the μc-Si:H single-junction solar cells. In addition, the different back reflectors applied to the μc-Si:H solar cells were compared. By using μc-SiOX:H(n) as a replacement for both an n-layer and ITO, higher quantum efficiency (QE) and cell efficiency at the long wavelength were obtained. Meanwhile, the process can be simplified. We applied this BR not only to the single-junction solar cells but also the tandem and triple-junction solar cells. Similar trend of higher QE at the long wavelength was found in multi-junction solar cells. With optimized μc-SiOX:H(n), we obtained the optimal efficiency of 10.63 % in a-Si:H/μc-Si:H tandem solar cell, with short-circuit current density (JSC) = 10.36 mA/cm2, open-circuit voltage (VOC) = 1.36 V and Fill factor (FF) = 75.18%. The cell efficiency of 8.93 % was obtained in a-Si:H/a-Si1-YGeY:H/μc-Si:H triple-junction solar cell, with JSC = 6.31 mA/cm2, VOC = 1.98 V and FF = 71.52 %.