開發並優化以微晶矽氧作為N型摻雜與背反射層的微晶矽薄膜太陽電池於多接面太陽電池之應用

Abstract

本研究以開發微晶矽(μc-Si:H)薄膜太陽電池為基礎並將其應用於多接面太陽電池之半導體元件，藉由整合以下三個主要的研究方案：(1)在微晶矽(μc-Si:H)薄膜吸收層之成膜過程中，藉由控制氫氣氣體稀釋比例，提升其結晶均勻度，如此可以減少非晶矽(a-S:H)孵化層之厚度，並有利於光生載子收集；(2)開發並應用高電導、高氧含量之微晶矽氧(μc-SiOx:H)材料做為一整合的n型與背反射層，以利提升吸收層之光吸收量；(3)減少氫電漿效應在透光導電層(TCO)與矽薄膜之間的氧化還原反應，以利增加透光導電層的入光量與其跟矽薄膜的介面品質。 吸收層厚度1.4微米的單接面微晶矽(μc-Si:H)薄膜太陽電池，其效率已提升至7.49%：短路電流密度(Jsc)為20.86 mA/cm2、開路電壓(Voc)為0.51 V、填充因子(FF)為70.41%。此外，非晶矽/微晶矽(a-Si:H/μc-Si:H)雙接面太陽電池使用μc-SiOx:H(n)/Ag背反射結構得到10.63%的高轉換效率：Voc=1.37 V、FF=75.18%、以及上下電池加總的Jsc=22.75 mA/cm2；相對於傳統的μc-Si:H(n)/ITO/Ag結構，雙接面太陽電池主要的效率提升來自於下電池的Jsc增加。對於三接面太陽電池而言，在有效達到光捕捉管理的前提下，a-Si:H/a-Si1-yGey:H/μc-Si:H三接面太陽電池得到8.93%的轉換效率，而a-SiOz:H/a-Si1-yGey:H/μc-Si:H三接面太陽電池則提升至9.16%的轉換效率：Voc=1.99 V、FF=69.80%、以及上中下電池加總的Jsc=22.60 mA/cm2。 總結而言，本研究證實了太陽光能量(入射光波長300-1100 nm)能被多接面太陽電池有效地利用。此外，不需要背面氧化銦錫(ITO)的濺鍍製程，全電漿輔助式化學氣相沉積(PECVD)製程的太陽電池製備方法，不僅能簡化製程步驟，還能因免除了濺鍍製程的離子轟擊過程，故能保有較佳的介面品質。

We developed and characterized the microcrystalline silicon (μc-Si:H) based thin-film solar cell for the application of multi-junction devices by integrating the three approaches: (i) improving structural homogeneity in the film growth of μc-Si:H absorber (i-layer) deposition to reduce the incubation-layer thickness and to be able to facilitate the carrier collection, (ii) developing and employing highly conductive microcrystalline silicon oxide (μc-SiOx:H) with high oxygen content as an integrated n-type and back reflecting layer to enlarge the optical absorption in the absorber, (iii) alleviating tin reduction at TCO/Si interface to improve TCO optical transmission and interface quality. The 1.4-μm-thick single-junction μc-Si:H solar cell was significantly improved and exhibited a conversion efficiency of 7.49%, with Jsc=20.86 mA/cm2, Voc=0.51 V and FF=70.41%. As for the a-Si:H/μc-Si:H tandem-junction solar cell, the cell using the μc-SiOx:H(n)/Ag back reflecting structure exhibited a conversion efficiency of 10.63% with Voc=1.37 V, FF=75.18% and a summation Jsc of 22.75 mA/cm2. Compared to the a-Si:H/μc-Si:H tandem-junction cell using the conventional μc-Si:H(n)/ITO/Ag structure, the main improvement arose from the considerably enhanced bottom-cell Jsc. Based on light management, the a-Si:H/a-Si1-yGey:H/μc-Si:H triple-junction solar cell exhibited a conversion efficiency of 8.93%, and the a-SiOz:H/a-Si1-yGey:H/μc-Si:H triple-junction solar cell exhibited a conversion efficiency of 9.16%, with Voc=1.99 V, Jsc=6.60 mA/cm2, FF=69.80% and a summation Jsc of 22.60 mA/cm2. In conclusion, this study has demonstrated that the solar energy can be utilized effectively via the enhanced broadband absorption achieved by the application of multi-junction devices. Furthermore, no need for back ITO sputtering revealed an all in-situ PECVD process would simplify the cell fabrication process and result in better interface quality due to the elimination of ion bombardment damage during ITO sputtering.