以高分子及兩種小分子之三項主動層及以氫氧化鉀處理氧化鋅電子傳輸層改善垂直相分離來增加有機太陽能電池能量轉化效率

Enhancing Power Conversion Efficiency of Organic Photovoltaics with Ternary Blend Incorporating One Polymer and Two Small Molecules and Inducing Vertical Phase Separation with Potassium Hydroxide Treated Zinc Oxide Electron Transport Layer

鄭皓文(Hao-Wen Cheng)

指導教授 ： 韋光華

國立交通大學/工學院/材料科學與工程系所/博士(2020年)

摘要

能源在我們現代人當中扮演著非常重要的角色，化石能源一直以來是我們的能量主要供應源，相對於化石能源，有機太陽能電池擁有成本低、可撓性、半透明等多功能應用之優勢。近年，在有機太陽能電池研究中，科學研究人員主要致力於在予體及受體的分子設計、主動層形貌調整、界面與界面之間及元件結構上改善，至今，有機太陽能電池在美國再生能源國家實驗室驗證之最高光電轉換效率已經達17%。在本論文中，研究重點為在為有機太陽能電池效能提升之方法進行研究，並分為兩部份：一、目前高效率有機太陽能電池的組成多為寬帶隙的予體及窄帶隙的受體，雖然這種組合擁有較寬的吸收光譜，但是整體上的外部量子效率仍偏低；加上，由於窄帶隙的受體通常擁有較深的最低未占分子軌域能隙，導致整體元件開路電壓較低，因此我們利用一個高分子予體及兩個小分子受體形成之三項主動層來同時提高開路電壓及短路電流來提升有機太陽能電池整體光電轉化效率。二、理想中主動層應擁有漸成予體與受體垂直向濃度分布，高予體濃度位於陽極界面及高受體濃度位於陰極界面，然而，大多數予體與受體在成膜的過程中使得予體與受體是均勻塗佈及分散在主動層中，這導致電荷在被抽取的過程中產生相對多的複合機率，因此，我們利用鉀離子殘留的氧化鋅電子傳輸層表面來誘導主動層中之垂直相分離，並利用密度泛函理論計算出小分子受體與鉀離子殘留之氧化鋅表面束縛能為高分子予體與鉀離子殘留之氧化鋅表面束縛能的兩倍，使進一步得到與理想主動層相近之垂直向分布，提升電子在元件中被抽取的能力，以提升整體有機太陽能能量轉換效率。

關鍵字

有機太陽能電池 ； 能源材料 ； 綠色能源 ； 有機半導體 ； 太陽能電池元件

並列摘要

Organic photovoltaics (OPVs) have many advantages such as low-cost fabrication, flexibility and semitransparency, leading to many applications. In the recent years, researchers focused on the donor/acceptor molecules designs, morphologies of the active layers, and the improvement of the device structures. So far, the certified power conversion efficiency (PCE) in National Renewable Energy Laboratory have reached 17%. In this dissertation, my research focused on the device engineering of OPVs and will be divided into two parts as following: (i) a wide bandgap polymer donor and a narrow bandgap non-fullerene acceptor based OPVs show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand the absorbance spectra from ultraviolet to near infrared region, the overall external quantum efficiency of device suffers low values. The other one is the low open-circuit voltage (VOC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital of the narrow bandgap. Therefore, we utilize the versatile third component as the second acceptor to elevate VOC and short-circuit current to improve power conversion efficiency of OPVs and (ii) an ideal BHJ structure would possess gradient distributions with high donor-rich near anode and acceptor-rich near cathode for efficient charge extraction. The random mixing of donor and acceptor in BHJ, however, often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we describe a new approach—treating the surface of the zinc oxide (ZnO) electron transport layer with potassium hydroxide—for inducing vertical phase separation of an active layer incorporating the small-molecule acceptor. Density functional theory calculations suggested that the difference in the binding energy for the acceptor and the polymer with the K-presenting ZnO interface is twice of that for the acceptor and the polymer with the untreated ZnO surface, such that it would induce more aggregation of the acceptor toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. The improved vertical phase separation leads to efficient charge extraction ability and enhancement in PCEs.

並列關鍵字

Organic solar cells ； Organic photovoltaics ； Energy materials ； Green energy ； organic semiconductors ； solar cells devices

參考文獻

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