低成本倒置有機太陽能電池載子傳輸效益改善與分析

能源議題近年來廣泛受到重視，太陽能電池具有用之不竭以及乾淨環保優勢，是解決人類未來能源問題的重要方向。在各種太陽能電池當中，有機高分子太陽能電池被視為可取代矽基板材料的下世代技術，該系統相較於矽基板太陽能電池有更好的成本效益，除此之外也有輕量化、可製作在可撓基板等優點，本研究針對高分子太陽能電池技術進行改良，以增進元件光電轉換效率。本論文以低能隙倒置結構高分子太陽能電池為基礎，透過一系列改良其載子傳輸效益的方法，不論是傳輸效率的改善還是載子生成量的增加，來達成低成本高效率的研究目標。其中在PBDTTT-C-T:PC71BM系統中，探討低能隙高分子太陽能電池以溶液製程控制形貌的方法，利用簡單的溶液製程改良方式來改善有機異質混層結構的高分子與富勒烯衍生物的分佈，形成理想的電子施體與受體交錯情形與提升激子產生介面區域。並且探討適當的旋轉塗佈速率來強化載子產生與收集，形成兼具吸收與載子傳輸優點的主動層厚度。成功改善有機太陽能電池的主動層材料分佈型態，並且最佳元件轉換效率達到5.27%。使用此法改良形貌增進效率，方法不僅簡單，也可被應用於多數倒置低能隙材料有機太陽電池系統。由於有機材料載子遷移距離短，因此有機主動層內部載子不易傳導出來。因此研究中也建立深入主動層中萃取載子的方法。成功地藉由調整水熱法生長氧化鋅奈米柱的成長環境的生長液配方，系統性地控制了氧化鋅奈米柱陣列的形貌，包括柱長、柱徑、柱間距與柱密度。並且統和這些因子，計算出長柱所增加的理論總表面積。氧化鋅奈米柱有增加主動層有效利用區域的效益，透過控制氧化鋅奈米柱和主動層接觸的總表面積以及柱間距，以及探討柱間距對於主動層滲入氧化鋅奈米柱的影響，可以大幅增加元件短路電流和轉換效率。對於PBDTTT-C-T:PC71BM倒置結構太陽能電池，適當的長柱形貌能大幅提升有機主動層中載子利用的效率，使太陽能電池元件短路電流達到16.8mA/cm2的高電流密度表現，而元件光電轉換效率能提升到7.26%。另外此方法因為是作電子傳輸層的形貌改善，因此和有機主動層內部的材料分佈控制能夠獨立操作，而對於元件表現的影響也能夠加成。因此這個方法對不同有機物材料具通用性。使得材料研發與元件製程的研究能夠各自獨立開發而不衝突，達到良好的合作。本研究證實這些方法的確也能成功提升另一系統PTB7:PC71BM的元件表現。但為了繼續提高元件效率，有機太陽能電池還有元件吸收量不足的問題需要改善。本研究成功利用添加金奈米粒子於有機太陽能電池主動層中來增加吸收表現。並整合主動層材料分佈型態與氧化鋅奈米柱陣列作法的作法，選擇適當粒徑的金奈米粒子分散於主動層溶液中並滲入氧化鋅奈米柱陣列裡，同時增加元件吸收與載子傳輸的效果。在調整適當的金奈米粒子濃度後，可以盡可能降低漏電流與能階問題的負面影響。另外提出複合兩種金奈米粒子粒徑應用的作法，來更加發揮表面電漿效應提升元件吸收，同時避免大粒徑卡在奈米柱表面的問題，在適當的大粒徑金奈米粒子旋鍍轉速控制後，能達到元件高短路電流的效果並保持良好的開路電壓和填充因子。最後是控制此元件製作架構下的電洞傳輸層氧化鉬厚度來最佳化元件表現。經過所有最佳條件處理，PTB7:PC71BM系統倒置有機太陽能電池可以達到7.86%的高光電轉換效率。另外，將本論文章節研究之方法和另一位同學之技術結合後，證實能將元件表現提升到超過8%，是奈米結構太陽能電池的一大突破。

關鍵字

高分子太陽能電池；溶液製程；倒置結構；低能隙材料；形貌控制；混合溶劑；添加劑；氧化鋅奈米柱；載子傳輸；金屬表面電漿效應

並列摘要

Solar energy, with its features of inexhaustibility and cleanness, is the most promising technology for solving the energy crisis and achieving sustainable development in the future. Among the various kinds of solar cells, organically based solar cells are regarded as the next generation of technology that will replace silicon-based cells because of the advantages of low cost, light weight, and mechanical flexibility. In the study, polymer solar cell technology has been improved to enhance its conversion efficiency. In this dissertation, it is mainly focus on solution processed inverted polymer solar cell systems. To reach the research target of low-cost and high efficiency, several approaches of carrier transport and carrier generation have been investigated. In the study of PBDTTT-C-T:PC71BM low-bandgap system, solution processed active layer morphology control methods have been developed. Some simple solution processed methods including mixed solvent and additives, have been used to improve the distribution of polymer and fullerene derivatives in heterojunctional active layer, forming ideal electron donor and acceptor morphology and increasing excitons generation area. Besides, proper active layer spin speed has been discussed to improve carrier generation and collection. These methods improve the morphology successfully and enhance the device conversion efficiency to reach 5.27%. Because of the short carrier diffusion length, carriers in the active layer are hard to be collected. As a result, ZnO nanorod array has been applied to provide a large number of carrier extraction channels deeply inside the active layer. We found a method of effectively controlling the ZnO nanorod array morphology. The ZnO nanorod array morphology parameters, including length, diameter, spacing, and density, were able to be controlled by adjusting the ratio of zinc nitrate and hexamethylenetetramine (HMT) in a growth-promoting solution to create different environments for hydrothermal growth. We also found that the contact area between ZnO nanorods and the active layer could be maximized with this ZnO nanorod array morphology control method, and the condition of the active ink infiltration could be improved. As a result, PBDTTT-C-T:PC71BM low-bandgap solar cells perform high short circuit current 16.8mA/cm2, and the device efficiency improved to 7.26%. The device improving process of PBT7:PC71BM system shows that these methods can be applied to other low-bandgap system successfully. However, to reach higher device efficiency, the problem of insufficient absorption needs to be ameliorated. In this dissertation, the approached of applying Au nanoparticles in nanostuctural polymer solar cells has been developed. The localizd surface plasmonic resonance and particle scattering effect promote active layer absorption, generating more carriers. The proper size-choosed Au nanoparticles combined with ZnO nanorod array to increase absorption and carrier extraction simultaneously. On the other hand, the new concept of combination of adding two sized Au nanoparticles in active layer has been deveploed, therefore, absorption increase resulting high short circuit current and fill factor. By proper controlling spin-coating speed of large sized Au nanoparticle, the device performance has a breakthough of ZnO nanorod polymer solar cell. Finally, the thickness of hole transport layer molybdenum oxide has been experimented to optimize PTB7:PC71BM system solar cells. The optimized device, which follows the rule of low-costs, has over 8% conversion efficiency. These approaches promote the development of inverted organic solar cells to a new milestone.

並列關鍵字

polymer solar cells ； solution process ； inverted structure ； low-bandgap ； morphology control ； mixed solvent ； additives ； ZnO nanorods ； carrier transport ； localized surface plasmonic resonance ； particle scattering

參考文獻

第一章

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低成本倒置有機太陽能電池載子傳輸效益改善與分析

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