| 摘要: | 在眾多太陽能電池種類中，就屬三五族堆疊型太陽能電池效率最高，其轉換效率可以達到44%，而目前多數的堆疊型太陽能電池是以鍺基板來成長三五族材料，但成本卻較矽晶太陽能電池高，矽除了便宜外，發展也相對成熟，故以矽基板取代鍺基板是未來研究的一大方向。
本研究主要探討鍺薄膜於矽基堆疊型太陽能電池中的特性與影響，並使用模擬的方式來分析堆疊型太陽能電池中的各層特性，透過調變各層薄膜的厚度與濃度，研究其各層電池的電流匹配值。從模擬中發現，當磷化銦鎵厚度為1400奈米，砷化鎵厚度為290奈米，本質鍺薄膜在30奈米時，其電流匹配值為12.8mA，轉換效率為32.3%。
在矽基堆疊三五族太陽能電池之中，製作底層矽基太陽能電池有多種的方式，例如爐管擴散法、離子佈植法或化學氣相沉積法。而本實驗主要使用離子佈植方式製作底層矽基太陽能電池，並利用退火修復離子佈植造成的缺陷。實驗結果顯示，在900度2分鐘退火所量測到的X光繞射半高寬值為最佳，最後得到的太陽能電池轉換效率達到10.9%。
最後，探討鍺薄膜成長於矽基太陽能電池上的光性和電性，與底層矽基太陽能電池效率。結果顯示，在鍺薄膜厚度的增加下，X光繞射半高寬值有變低的趨勢，在電性方面，厚度增加下，其薄膜缺陷變多而使片電阻值增大；光性方面則是厚度越厚，在長波長的穿透率則越低。在成長完鍺薄膜後經過700度5分鐘的退火，X光繞射半高寬可達到358.56 arcsec，而成長完鍺薄膜後蝕刻對離子佈植矽基太陽能電池的轉換效率降低約0.6 %。
;III-V compound tandem solar cells that combine low and high bandgap materials tailored to the incident solar spectrum have very high conversion efficiencies (~44%). However most of the III-V tandem solar cells are grown on Ge or GaAs substrates, both are more expensive than Silicon substrate. In spite of unmatched performance of III-V solar cells, silicon not only have lower price in the market but also have mature technique. Therefore, germanium substrate replaced by silicon substrate is the main direction of research in the future.
In this study, we focused on the characteristics and influence of germanium thin film depositing on silicon solar cell. At first, we use PC1D simulation software to analyze and modulate thickness and concentration of each layer and find the current-matching value. From the simulation results, we found that when the thickness of gallium indium phosphide (GaInP) film is 1400nm, gallium arsenide (GaAs) film is 290nm and germanium (Ge) film is 30nm, we got the current-matching value is 12.8mA, conversion efficiency is 32.3%.
There are many methods to fabricate the silicon solar cell (Bottom cell), such as diffusion, ion implantation or chemical vapor deposition. We use method of ion implantation to fabricate silicon solar cell in our experiments. After ion implantation process, we use anneal to repair defects caused by ion implantation. Experimental results show that when we anneal at 900 °C for 2 minutes, the best full width at half maximum (FWHM) we can measured. The result of silicon solar cell conversion efficiency is 10.9%.
Finally, we discuss the optical and electrical properties of germanium thin films grown on silicon solar cell. The results showed that the thickness of the germanium thin film increases, the best values of FWHM we can obtain. In terms of electrical properties, as the thickness of germanium film increases, the defects and sheet resistance value increase. In terms of optical properties, as the thickness of germanium film increases, the transmittance at long wavelength decrease. After growing the germanium film at annealing 700 °C for 5 minutes, we can obtain the value of FWHM is 358.56 arcsec. When we grow the germanium film and then etching it on silicon solar cell, we measured the conversion efficiency decreased by 0.6 %. |
