主動層 PTB7:PC71BM 製備倒置型高分子太陽能電池及其元件特性研究

Abstract

在這篇論文，我們討論PTB7:PC71BM運用在倒置型高分子太陽能電池。高分子太陽能電池有非常多的優點，包括低成本製程、具機械上的彈性、大面積滾輪製造、製程簡單和質量輕，因為這些優點，科學家致力於研究高分子太陽能電池。高分子太陽能電池的進步來自於材料上的創新以及元件結構上的工藝，最近一個新穎的高效率主動層材料被發明出來，此材料為PTB7:PC71BM，這個令人驚艷的材料有著破紀錄的效率，很多研究都投入在這個材料上。這篇論文著墨於元件結構上的創新，以期許效率可以往上進行突破，在此同時其相關的機制也被探討。 在第二章，介紹一些基本原理和機制。部分原理與無機太陽能電池是一樣的，無機太陽能電池的相關機制已經被發展完善，然而在高分子太陽能電池裡有些機制仍然不清楚，因此更多相關的細節在這個章節被拿來探討。 在第三章，探討使用氧化鋅當作電子傳輸層以及其相關的應用。電子傳輸層在倒置型高分子太陽能電池相當重要，因為ITO的功函數高的關係，所以電子傳輸層可以拿來降低陰極電極的功函數以阻止空間電荷效應和減少載子複合。此外，氧化鋅非常適合拿來當作電子傳輸層，因為它具有高導電度和高穿透度。這邊比較一些常見的主動層材料搭配氧化鋅當作電子傳輸層，除此之外，多層氧化鋅結構可以更平坦的與主動層接觸，所以搭配兩層氧化鋅薄膜其效率可以達到6.25%。另外值的一提的是氧化鋅可以拿來做多種的奈米結構，一個解決主動層擴散長度短的極佳方法為將氧化鋅柱插入主動層中，氧化鋅柱可以提供一個新的通道來傳輸載子，因此載子可以被有效的萃取，電流密度大量的提升使其效率來到7.56%。然而氧化鋅柱的長度是很重要的課題。 在第四章，PEIE和PFN被用來改變ITO和氧化鋅的功函數。報告指出PEIE有能力降低多種材料的功函數，在這章裡，PEIE被用來降低ITO和氧化鋅的功函數，因此介面上的能階調變被有效的改善，在兩層氧化鋅上塗佈PEIE有較佳的效率為6.56%。然而PFN也有相同的能力改變ITO和氧化鋅的功函數，三層氧化鋅上塗佈PFN有很明顯的提升，效率6.78%來到更高的境界。最後，電洞傳輸層和陽極電極也被優化，優化後的元件效率達到6.84%且FF有62.73%。 最後總結這篇論文，多種元件結構上的工藝被探討。這些工藝更進一步推升效率到達另一個境界，而且它們可以被用在新的高效率材料，然而必須花費更多的心力投注在提升高分子太陽能電池。

In this thesis, the inverted polymer solar cells using PTB7:PC71BM as an active layer is studied. The potential advantages of polymer solar cells are numerous, including the low-cost of the process, mechanical flexibility, the ability for large area roll-to-roll processes, easy production, and light weight. Dependent clause researches have made great efforts on studying polymer solar cells. The improvements of polymer solar cells could result in both material innovation and state-of-the-art device architecture. Recently, a novel high efficiency active layer material was invented, which is PTB7:PC71BM. This promising material gives polymer solar cells a record high efficiency. Various research has studied this material. The state-of-the-art architecture is focused on this paper to further push the efficiency to another level, also the mechanics are discussed. The basic principle and mechanics are introduced in chapter 2. Some of the concepts are the same with inorganic solar cells. The mechanics of inorganic solar cells have been fully developed. However, some of the mechanics in polymer solar cells are still dubious. Hence, more details have been discussed in this chapter. In chapter 3, using ZnO as an electron transport layer and its further applications are discussed. The electron transport layer is relatively important in inverted architecture polymer solar cells, compared to conventional architecture polymer solar cells. Due to the high work function of ITO, the electron transport layer could lower the work function of the cathode electrode, preventing space charge effect; and hence, reducing the carriers recombination. Moreover, ZnO is an outstanding candidate to serve as the electron transport layer due to its high conductivity and transmittance. Some common active layers are compared using ZnO as an electron transport layer. In addition, multi-layers ZnO thin film could provide a smooth contact with the active layer; raising the power conversion efficiency to 6.25% with two layers ZnO thin film. It is noted that ZnO could exhibit a variety of nanostructures. An excellent solution to solve the short diffusion length of the active layer is to insert ZnO nanorods into the active layer. ZnO nanorods could provide an alternative tunnel to transport carriers. As a result, the carriers could be efficiently collected. The power conversion efficiency comes to 7.56% due to the enhancement of current density. Nevertheless, the ZnO nanorods length is a critical issue. In chapter 4, PEIE and PFN are introduced and used to modify the work function of metal or metal oxide. PEIE is reported to have the ability to lower the work function of variety materials. PEIE is used in this chapter to lower the work function of ITO and ZnO; and hence, the interfacial energy alignment has a better improvement. The device with PEIE on the top of two layers ZnO thin film has a better power conversion efficiency of 6.56%. Since PFN has the same ability to modify the work function of ITO and ZnO, a great enhancement is presented in the device with PFN on the top of three layers ZnO thin film. The power conversion efficiency comes to a higher level of 6.78%. Finally, the hole transport layer and anode electrode have been optimized. The optimized device has power conversion efficiency of 6.84% and FF of 62.73%. In conclusion, various state-of-the-art architecture have been discussed. The state-of-the-art architecture further pushes the efficiency to another level. Besides, they could be used, when a novel high efficiency material is invented. Nevertheless, great effort but more needs to be done.