背接觸電極砷化鎵薄膜太陽能電池製作之研究

對於單接面的太陽能電池而言，砷化鎵是一種極好的材料，由於其材料特性為直接能隙可以有效率的吸光和發光，且擁有良好的輻射硬度及低溫度係數，所以砷化鎵太陽能電池被廣泛的使用在太空應用及聚焦光伏特系統中。理論上在AM1.5G的光譜下單接面砷化鎵太陽能電池的轉換效率高達33.5％。在過去40年來高效率的背接觸矽太陽能電池已經被廣泛探索且擁有許多背接觸式的設計。主要藉由將全部或部份的正面電極移至元件的後面來降低遮蔽的損失，以提升元件的效率。但不論是一般結構或是背接觸式的矽太陽能電池，由於材料本身是間接能隙且吸光係數低，所以往往需要數百微米厚的作用層來吸光，相較之下，砷化鎵只需幾微米的厚度便能吸收其吸光波段99%的光，所以砷化鎵太陽能電池更適合薄膜化及背接觸式的設計。在此研究中，我們先利用程式對背接觸電極砷化鎵太陽能電池進行特性的數值模擬，利用模擬結果去設計磊晶結構及元件的製作流程，然後我們同時結合磊晶剝離(Epitaxial Lift-off)技術將砷化鎵磊晶層從砷化鎵基板上轉移到可撓式的基板，來製作一輕薄且可撓式的薄膜太陽能電池。接著我們藉由量測I-V特性曲線及量子效率來確認太陽能電池的特性，在AM1.5G下，其轉換效率可達到20.904%，電流密度為25.420 mA/cm2。且在p電極間距及抗反射膜的優化條件下，其轉換效率達21.104%，電流密度25.732 mA/cm2。由數據顯示出薄膜太陽能電池在背接觸設計下的潛力，且若後續再針對此結構進行優化再配合上砷化鎵基板的再利用製程，將可實現一個低成本且高轉換效率的薄膜太陽能電池。

關鍵字

薄膜太陽能電池；背接觸電極；磊晶剝離

並列摘要

For single junction solar cell, GaAs is an excellent material due to its material properties such as direct bandgap can effectively absorbing and emitting light, good radiation hardness and low temperature coefficient make GaAs solar cells extensively used for space applications and concentrated photovoltaic systems. Single-junction GaAs solar cells can be as high as 33.5% under AM1.5G illumination in theory. The high efficiency back-contact silicon solar cells have been extensively explored, and many designs of back-contact type have been suggested during the last 40 years. Cells can achieve potentially higher efficiency by moving all or part of the frontside electrodes to the rear of the device to eliminate shading losses. Whether silicon solar cells were made in the conventional type or in back-contacted structure, it always needs hundreds micrometers of active layers to absorb the visible light due to its indirect bandgap and lower absorption coefficient. Compared with silicon, GaAs solar cells can absorb 99% light in the few micrometers is more suitable for thin-film devices and back-contacted design. In this study, we started to numerically simulate the performance of back-contact GaAs solar cells by using our in-house developed program, and use the results to design the epitaxial structure and process flow, then we combine the epitaxial lift-off technique to transfer the GaAs epilayer from the GaAs substrate to the flexible substrate to realize a lightweight and flexible thin-film solar cells. And we measure the current-voltage characteristics and quantum efficiency to confirm the performance of solar cells, under AM1.5G illumination, the conversion efficiency can achieve 20.904% and current density is 25.420mA/cm2. After optimization the p-electrode spacing and the anti-reflection coating, the conversion efficiency is 21.104% and current density is 25.732 mA/cm2 . This approach brings the potential of back-contacted design to thin-film solar cells. With further investigation and optimization on this structure and combine GaAs substrate re-use process to achieve a low-cost, high-efficiency thin-film solar cell.

並列關鍵字

Thin-film solar cell ； Back-contact ； Epitaxial lift-off

參考文獻

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[19] Voncken, M.; Schermer, J. J.; Bauhuis, G. J.; Mulder, P.; Larsen, P. K. Multiple Release Layer Study of the Intrinsic Lateral Etch Rate of the Epitaxial

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背接觸電極砷化鎵薄膜太陽能電池製作之研究

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