以綠色製程與生物基高分子開發環境友善太陽能電池

Abstract

隨著環境意識增強，有機太陽能電池由於身為乾淨能源、低成本製造，並且可以溶液製備生產，因此近年來高度地蓬勃發展。不論是提高光轉換效率，亦或是延長使用壽命，中間層對於提高元件性能都有著舉足輕重的作用，然而僅僅是少量的研究將可再生材料用於中間層。在對此綠色能源進行探討時，透過中間層界面調控機制的進一步了解，進行材料開發與特性分析，逐漸走向結合綠色製程以及生物基高分子，包含了可溶於醇類的共聚物與生物聚離胺酸，以研發環境友善的有機太陽能電池。 首先在第二章，本研究設計合成一個可溶於環境友善醇類的交聯共聚物，新材料由不同比例的聚丙烯酸丁酯和聚乙烯基三唑組成，並利用交聯反應使其帶正電，同時增加本身的強度，應用於太陽能電池的電子傳輸層，以期能達到提高效率、增強穩定性的目標。以此交聯共聚物作為元件中間層，成功將光轉換效率提高接近四倍，而在連續加熱或照光1000小時後仍能維持初始的80%效率，此結果顯示此適用於綠色製程的新材料具有製備高效率高穩定性的有機太陽能電池之潛力。 在第三章研究天然高分子聚離胺酸的鏡像異構物特色應用於太陽能電池電子傳輸層。此種生物材料可以直接從大自然中取得，不但擁有環境友善的優點，同時藉著結合兩具立體中心的化合物以造成不同程度的偶極，透過左、右旋的立體構型不同，分成純聚左旋離胺酸和聚左旋離胺酸混參聚右旋離胺酸兩個組別，生成較強極性的中間層能更有效地在相應的界面進行功函數調控，從而達到促進電荷傳輸的功能。結果證實界面材料的功函數調控機制主要由極性程度所決定，且聚離胺酸中間層成功製備出提升了4.7倍的高轉換效率有機太陽能電池。 在第四章進一步研究生物高分子聚離胺酸應用於元件中間層的修飾層，探討其對於混摻吸光主動層的正面影響，進而達到提升效率與改善穩定性的效果，並且繼續應用於開發軟性太陽能電池。聚離胺酸作為修飾層，有效地影響了其後主動層的相形貌以及分子排列，優化的混摻系統傾向面朝上的堆疊排列，如此有利於電流傳輸顯著提高了元件的性能，最佳光轉換效率為15.3%，而其對主動層形貌的影響也同時提高了熱、光穩定性。此外嘗試將聚離胺酸應用於軟性元件，使用100%生物基高分子聚乙烯呋喃酸酯為基材，結果不但表明聚離胺酸的普遍適用性與其修飾中間層之潛力，也成功開發出同時使用生物性材料修飾層與軟板的環境友善有機太陽能電池。 因此本研究開發出可溶於環境友善溶劑的交聯共聚物，不但適用於綠色製程，並且結合生物性高分子，作為中間層應用於功函數調控與表面形態最佳化，成功製作出高效率高穩定性的有機太陽能電池，通往永續經營的發展方向。

With growing environmental awareness, organic photovoltaic (OPV) devices have been highly developed lately owing to being clean energy source, low-cost manufacture, and roll-to-roll solution production. Interlayer plays an important role on promoting the device performance including enhanced light-conversion efficiency as well as extended lifetime. However, renewable materials are only slightly explored as an interlayer in OPV. By further understanding the underlying mechanisms of interlayer, bio-based materials and green process are explored to fabricate an eco-friendly OPV in this thesis, including alcohol block copolymers and bio-based poly-lysine. In chapter 2, a series of alcohol-soluble cross-linked block copolymers (BCPs) poly(nBA)n b poly(NVTri)m (named as PBAn-Trim), consisted of poly(n-butyl acrylate) (poly-(nBA)) and poly(N-vinyl-1,2,4-triazole) (poly(NVTri)) blocks were prepared and served as the electron-extraction layer (EEL) in OPVs. After taking the crosslinking reaction, the ionic functionality was largely increased by forming a triazolium cation forming more effective interfacial dipoles to adjust its WF, and the structural robustness was able to be further rectified. The PBA70-Tri30 based OPV device improved by almost four times for power conversion efficiency (PCE) and more than 80% of its initial performance was retained after being heated at 60 °C for 1000 h or exposed under continuous illumination (1 sun) for 1000 h. It suggests that PBAn-Trim is a green processing EEL of high performance OPVs with superior thermal stability and photostability. In chapter 3, bio-based poly-lysine and its enantiomers were employed as EELs in OPVs to verify their work function (WF)-tuning capabilities, including poly-L-lysine and poly-L-lysine blend poly-D-lysine. These two poly-lysine groups, with different arrangements of the amino groups that built up different surface dipoles, altered the surface energy and WF of indium tin oxide (ITO). Poly-L-lysine possessed intense ionic functionality, revealing well capability to form effective interfacial dipoles interface to facilitate the charge transport at the corresponding interface. The WF-tuning functions lied strongly in the polarity increase and thus poly-L-lysine was discovered to be an efficient green interlayer presenting a high increase of 4.7 times in PCE. In chapter 4, the green poly-lysine was further applied as an interfacial layer (IFL) of EEL and the subsequent morphology evolution of active layers was studied for enhanced efficiency and stability in OPVs. By embedding poly-lysine as IFL, it not only observed the changes of the blend film phase segregation but also enhanced the molecular packing in the preferential face-on orientation. The optimized blend film morphology facilitated the carrier extraction, thereby significantly enhanced the OPV performance with the best PCE of 12.5% and 15.3% for the PBDB-T-2Cl:IT-4F and PBDB-T-2F:Y6 blends, respectively. Moreover, the poly-lysine on changing BHJ morphologies also greatly improved thermal- and photo-stability. Besides, poly-lysine could be used to fabricate a flexible OPV on renewable polyethylene furandicarboxylate (PEF) substrate. It was proved the general applicability of poly-lysine film, besides the bio-based IFL and substrate were successfully incorporated to develop flexible OPV showing great environmentally friendly potential. In summary, the green solvent processable block copolymer and bio-resourced polymers were successfully employed as the interlayer to tune the work function or morphology, which led to high performance OPVs for sustainable development.