有機太陽能電池中之奈米結構之應用與分析

在有限的石化資源以及綠色能源意識抬頭下，太陽能領域已經受到了很大的關注。而在太陽能領域中，有機高分子太陽能電池具備了製程簡單、可大面積生產、溶液製程、可撓曲性、設備低廉…等多方位的優點，因此也是最有潛力的太陽能電池，許多關於高效率的有機高分子太陽能電池已經被報導出來。根據之前研究文獻表示，對於提昇低能隙高分子材料與PC71BM系統的轉換效率已經有不少方法，如常見的慢乾法、不同比例混合溶劑、改變施體受體比例、添加劑的搭配及濃度。但是這些方法必須針對不同材料特性作對應的控制和變動，換句話說，這些方式並不是互相通用的。為了可以有通用的方式來增進倒置結構的有機太陽能電池表現，在本研究中，我們成長氧化鋅奈米柱於元件中建立柱狀結構，為了繼續保有有機高分子太陽能電池的優點，我們使用製程簡單、可大面積生產、低成本的水熱法來生長氧化鋅奈米柱。在過去的報導中，太陽能電池元件所產生的激子因為有擴散長度的問題，使得主動層厚度受到限制，因此，我們使用氧化鋅奈米柱取代原本只是薄膜的氧化鋅電子傳輸層成為柱狀的電子傳輸通道，在主動層滲入氧化鋅奈米柱柱狀結構後，縮短了主動層和氧化鋅之間的距離，由於減少了電子電洞對複合的機會並可更有效率地將電子傳導至電極以致於元件表現受到提昇。為了使主動層可以和氧化鋅之間有良好的接觸以發揮其傳輸電子的功效，我們藉由不同的生長時間、生長液濃度控制氧化鋅奈米柱形貌，使得主動層得以順利滲入於柱狀結構，並且也使用不同的有機主動層系統應用在此一氧化鋅奈米柱平台，開創出一個具有通用性的方式來增進元件表現。本論文第一部分先將低能隙高分子材料應用在氧化鋅奈米柱平台上，我們是使用的是PBDTTT-C/PC71BM系統。由於低能隙高分子主動層厚度較P3HT系統薄，氧化鋅奈米柱的長度需要更精準的控制，我們使用不同時間控制奈米柱形貌，使有機主動層可以正常工作，且元件效率可以從4.67％增加至6.07％。第二部分由於我們發現到奈米柱間距是影響元件表現的重要因素，無機奈米柱和有機主動層的接觸非常重要。因此，我們調整生長液濃度改變奈米柱間距，使得其形貌可以更匹配有機主動層，在調整控制奈米柱形貌之後，我們再度應用另一有機主動層材料PBDTTT-C-T/PC71BM，並使其效率從5.40％提升至7.34％。最後，為了將氧化鋅奈米柱效益更能發揮，我們研究如何在保持奈米柱的間距下，可以成長出更長的奈米柱。我們使用二次長柱，以第一次長柱控制間距，第二次長柱控制長度，此方法有效的讓主動層厚度增加，可以轉換更多光電流。我們利用此方法應用在PBDTTT-C-T/PC71BM以及PTB7/PC71BM兩種系統，使元件效率分別可以到達7.8％以及8％。

關鍵字

太陽能電池；高分子；形貌；氧化鋅奈米柱；倒置結構；奈米

並列摘要

Under the circumstances of finite petrochemical resource and the uprising awareness of green energy, solar energy has grabbed tremendous attention. In the field of solar energy, polymer solar cell has the best potential among other solar cells by taking its various advantages such as, easily manufactured, flexible, low cost, solution process and large-scale manufacturing available. The high power conversion efficiency(PCE) of polymer solar cell has been reported. According to the previous studies, there were plenty of methods which have been adopted to enhance the PCE of low bandgap polymer material and PC71BM system, such as slow drying, different ratio of donor and accepter, additive solvent and adjusting its concentration. However, these methods need to be modified according to the variance in material characteristic. In other words, the above-identified methods is not universal. In this experiment, in order to enhance the performance of inverted structural polymer solar cell by a universal method, we grew ZnO NR in the device and built up the nano structure. Besides, for keeping the advantage of organic solar cell, we take the hydrothermal treatment which is low cost, large-scale fabrication and easily processed to grow ZnO NR and as well as to control the morphology of the nanorod. In the past reviews, there was some limitation on the thickness of active layer because of its’ diffusion length of carriers. Therefore, we substituted the ZnO NR for ZnO film, electron transport layer, as the electron transport channel. After the active layer filled into the space of ZnO NR, it shortened the distance between the active layer and ZnO. When the possibility of electron-hole recombination are reduced and the electron is transported more efficiently to the electrode, the performance of the device would be enhance. In order to advance the contact between active layer and ZnO and perform better on transferring electron, we adopted different growth time and different concentration of growth solution to control the morphology of ZnO NR which enables the active layer to fill into the space between the ZnO NR. Also, we applied different systems of organic active layer on this ZnO NR platform to come up a universal method to enhance the performance of the device. First, we applied the ZnO nanorod array on low bandgap organic material system, PBDTTT-C/PC71BM. Because the thickness of active layer of low bandgap material is thinner than P3HT system, the growth and morphology of ZnO nanorod array are difficult to control. We control the ZnO nanorod array by different growth time. With the proper morphology of ZnO nanorod array, the organic active layer can work on this treatment and the PCE is improved from 4.67% to 6.07%. In the second part, we found that the space between the ZnO nanorods and contact with organic layer are very important issue with the performance of the device. Therefore, we controlled and enlarged the space by different growth solution concentration of ZnO nanorod to fit the organic active layer. After the morphology of ZnO nanorod array is optimized, the performance of the device with other organic system PBDTTT-C-T/PC71BM is increased from 5.40% to 7.34%. Then, in order to make the ZnO nanorod array work more effectively, we researched how to have the longer length of ZnO nanorod with stable space between nanorod. Through twice ZnO nanorod growth, the first time growth is control of space and the second is control of the nanorod length, we make the better morphology of ZnO nanorod array than single growth. As a result, with more photocurrent, the performance of organic system PBDTTT-C-T/PC71BM and PTB7/PC71BM are improved to 7.8% and 8%