具全方向抗反射奈米線結構之高效率背接面PEDOT:PSS/n-Si混合式太陽能電池

Abstract

目前的PEDOT:PSS/n-Si混合式太陽能電池中，因有機層置於照光面會吸收部分光源，而在效率方面受到限制，且正接面(Front-junction)太陽能電池的背面，也大多無法有效地進行鈍化處理。本論文將PEDOT:PSS至於背光面形成背接面(Back-junction)，搭配表面電場(Front surface field)與SiNx抗反射層，可在沒有任何表面粗糙結構情況下達到超過11 %的轉換效率，改善前述問題。而為了增加光吸收，本論文在電池表面製作金字塔與奈米線結構，使轉換效率分別達到13.9 %與14.5 %。此外，相較表面為金字塔結構的元件，本論文也發現表面為奈米線結構的元件具有全方向的光捕捉特性(Omni-directional light-trapping characteristics)，使得在不同入射光角度(0-60°)情況下，可以維持其效率。 另一方面，本論文亦將電極同時置於背光面，使照光面沒有任何金屬遮蔽效應而增加了載子收集，但短路電流並沒有如預期地增加。研究結果顯示，這是因製作的電池結構缺少提供側向電流擴散的電場所導致。

Current poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/n-Si solar cells have limited efficiency because the heterojunction was located on the front of the cells that resulting in a parasitic light absorption within the organic material layer. And the rear surface of those front-junction solar cells was usually poorly passivated. To improve aforementioned shortcomings, we fabricated back-junction PEDOT:PSS/n-Si with front-surface field and SiNx anti-reflection layer but no front surface textures, which demonstrated a power conversion efficiency of over 11 %. By incorporating either a random pyramid or a nanowire anti-reflection structure to the front of the cell surface to enhance light absorption, the power conversion efficiencies were further enhanced to 13.9 % and 14.5 %, respectively. Moreover, cells with nanowire anti-reflection structure showed omni-directional light-trapping characteristics over the random pyramid structure and were able to maintain the power conversion efficiency even at an incident angle as large as 60 degrees. On the other hand, we also fabricated back-junction PEDOT:PSS/n-Si with back contact cross-finger type electrodes. Thus the front side of the devices would eliminate the shading loss and enhance carrier collection. However, the photovoltaic parameters of the cells were not improved as expected. It was attributed to the lacking of lateral diffusion driving force for carrier collection at the cross-finger type electrodes.