發n型微晶矽氧於非晶矽/非晶矽鍺串疊型薄膜太陽能電池作為中間反射層的研究

Abstract

在此研究，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，由於氫化非晶矽鍺具有低能隙可吸收長波長光譜的特性，所以非晶矽鍺太陽能電池適用於多接面太陽能電池的中間或底部電池。另一方面，氫化微晶矽氧材料隨著薄膜中氧含量的上升，可減少吸收並使得折射率降低，故可當成中間反射層於串疊型太陽能電池中，以增加反射到頂部的光及穿透更多光到底部而達到較好的電流匹配使短路電流提升，藉以更有效率的利用太陽能光譜而提升電池轉換效率。。由此可知中間反射層的需求條件為寬能隙、低折射率以及可接受的電導率，而其中氫化微晶氧化矽的氧含量及電導率為首要考量的因素。本研究著重在非晶矽/非晶矽鍺之雙接面太陽能電池的研究，最後此實驗中間反射層的優化能隙為2.09電子伏特，其導電率約為10-1 S/cm。此外，非晶矽鍺之雙接面太陽能電池亦有使用穿隧複合接面。最後實驗電池的開路電壓、短路電流密度、填充系數、轉換效率被提升至1.6 V、8.23 mA/cm2、70.3%及9.26%。

In this thesis, the thin-film tandem solar cells were prepared by a 27.12 MHz radio-frequency plasma-enhanced chemical vapor deposition (PECVD) system. The bandgap of the amorphous silicon germanium (a-Si1-XGeX:H) can be adjusted by Ge-incorporation. In addition, the a-Si1-XGeX:H material is suitable for the middle or the bottom absorber due to its higher optical absorption in long wavelength region. The a-Si:H / a-Si1-XGeX:H tandem cell was employed due to better utilization of solar spectrum. In order to improve the performance of a-Si:H / a-Si1-XGeX:H tandem solar cell, we introduced a n-type microcrystalline silicon oxide (μc-SiOX:H(n)) intermediate reflecting layer (IRL) between the top and bottom cells to reflect the light back to a-Si:H top cell and reduce the optical loss in a-Si1-XGeX:H bottom cell. Thus, the requirements of μc-SiOX:H(n) as IRL were larger bandgap, lower refractive index and acceptable conductivity. The oxygen content and the conductivity of μc-SiOX:H(n) were the critical factors to affect cell performance. The IRL was optimized to be wider bandgap and acceptable conductivity. In our results, the optimized bandgap of μc-SiOX:H(n) was 2.09 eV and the acceptable conductivity was approximately 10-1 S/cm. In addition, tunneling recombination junction (TRJ) layer was also employed in a-Si:H / a-Si1-XGeX:H tandem cells. As a result, we used μc-SiOX:H(n) layers as IRL to obtain optimum cell efficiencies. Finally, the open circuit voltage (VOC), short circuit current density (JSC), fill factor (F.F.) and conversion efficiency (η) of a-Si:H / a- Si1-XGeX:H tandem cell with the optimized μc-SiOX:H(n) IRL were improved to 1.6 V, 8.23 mA/cm2, 70.3% and 9.26%, respectively.