高效率敏化之太陽能光電元件

Abstract

近年來，具優越物理與化學特性之量子點材料發展迅速。其受到量子侷限效應影響，藉由調控量子點粒徑大小可得到不同發光波長。於過去研究中，相當多量子點材料應用於光電元件上，例如：發光二極體、背光顯示器、光偵測器與生醫光電等。於本研究中，我們成功設計一個新穎與高效率之混合型敏化太陽能電池，主要利用量子點獨特之吸光-發光特性，應用於單晶矽與砷化鎵太陽能電池表面上，可降低元件表面反射率、增加元件紫外光線收集機率與改善元件表面上載子傳輸特性。 於第一部份研究中，我們成功利用量子點改善單晶矽奈米柱陣列太陽能電池轉換效率，透過膠體微影術與離子反應蝕刻技術製作單晶矽奈米柱陣列，再結合量子點形成太陽能電池，於標準模擬太陽光條件照射下，結果顯示較高之功率轉換效率，相較於無量子點太陽能電池提升約為33％。由實驗分析結果顯示，其元件效率提升主要的機制為光子向下轉換機制、抗反射機制與表面載子傳輸之改善，此些特性皆為量子點層之作用。 於第二部份研究中，為驗證量子點材料是否可應用於其它型態之太陽能電池上，故我們量子點應用於傳統的砷化鎵太陽能電池表面上，使元件成為新穎混合型敏化的太陽能電池結構。藉由應用量子點於砷化鎵太陽能電池表面，於長波段區域可獲得有效抗反射機制，以及於短波長下獲得光子下轉換機制，原因可歸納為量子點於短波長下具較強之吸收並且同時轉換出可見光波段給太陽能電池所吸收，故相較於傳統無量子點之砷化鎵太陽能電池，光電轉換效率可提升18.9%。 於第三部份研究中，(由於過多量子點於使用下會造成自聚集現象，進而影響光子下轉換機制)我們有效減少過多量子點於使用下所造成自聚集現象，進而提升光子的下轉換機制。故我們使用可饒式矽氧樹脂薄膜製作出雙層量子點層並且成功應用於砷化鎵太陽能電池上。其中，將透過旋轉塗佈方式製作出之矽氧樹脂薄膜，之後引入量子點內形成層堆疊之雙層量子點層。而雙層量子點砷化鎵太陽能電池相較於傳統無量子點之砷化鎵太陽能電池可提高轉換效率高達22%。最後，由於量子點材料具可提升任何型態之太陽能電池轉換效率，未來極具潛力成為下一世紀新穎混合型敏化太陽能電池元件。

Quantum dots (QDs) material in recent years has rapidly developed because of exhibiting superior physics and chemicals properties. Significantly, QDs has the unique and the size-dependent absorption with emission properties due to quantum confinement effect. Therefore, in the past, there are many applications of QDs in optoelectronic devices, such as light-emitting diodes, backlight modules, photo-detectors, and bio-photonics. In this work, we successfully designed a novel and highly efficient hybrid solar cells. By applying the QDs material in traditional Si-based and GaAs-based solar cells to improve the surface reflection, light harvesting in ultraviolet region, and surface carrier collection properties. First part, we improved the power efficiency of the crystalline silicon (c-Si) solar cell with nanopillar arrays (NPAs) by deployment of QDs. The NPAs was fabricated by the colloidal lithography and reactive-ion etching techniques. Under a simulated one-sun condition, the device with QDs shows a 33% improvement of power conversion efficiency, compared with the one without QDs. It is noteworthy that the enhancement of efficiency could be attributed to the luminescent down-shifting, the antireflection, and the improved surface electrical property. Second part, to find out whether this hybrid type fabrication can be applied to other solar cell; we demonstrate a hybrid design of traditional GaAs-based solar cell combined with QDs. With anti-reflective feature at long wavelength and luminescent down-shifting at UV regime, the QDs effectively enhance the overall power conversion efficiency by as high as 18.9% compared to traditional GaAs-based device. Third part, we effectively alleviate the self-assembly phenomenon in high dosage of QDs and enhanced the luminescent down-shifting effect. This study demonstrates the high performance of GaAs solar cells with dual-layer QDs carried by flexible polydimethylsiloxane (PDMS) film. The flexible PDMS film was fabricated using the spin-coating technique, and was then used to embed dual-layer QDs. The proposed scheme enhances power conversion efficiency by 22%, compared to a GaAs solar cell without CdS QDs. Finally, this study shows the potential possibility method using QDs material in solar cells, which could increase the power conversion efficiency for any kind of solar cells, and should be considered for the design of next-generation solar cells.