低溫處理與氧化鉿阻擋層對於高分子太陽電池效率及穩定性之研究

Abstract

高分子太陽能電池的效率以及劣化問題廣為被研究與改善。而本篇針對以P3HT為電子施體和碳六十衍生物(PCBM)為電子受體的異質接面(Bulk Heterojunction)高分子太陽能電池，分別利用改變製程以及元件結構來達到效率的提升以及劣化的改善。 在本研究的第一部分(第二章)，我們利用低溫製程來改善元件物理性的形態劣化。相較於室溫乾燥過程，將高分子主動層在低溫的情況下乾燥成膜，可以增加P3HT的成核行為。並且在經過190度的熱退火後，密集的P3HT結晶提供更大的結晶度，並且阻擋PCBM的大規模聚集，使雙成分有很好的分散性。此高結晶的主動層型態提供4.3%的太陽能電池效率，同時其P3HT和PCBM緊密的型態提供了更好的的熱穩定性，改善了元件內因物理型態改變減少介面的劣化問題。 而本研究第二部分(第三章)專注於元件因不穩定的ITO導電玻璃和電洞傳輸層(PEDOT)所造成的化學性劣化。電洞傳輸層(PEDOT)在吸收水氣之後會侵蝕ITO導電玻璃，釋放出銦離子。為了解決這樣的化學劣化，我們利用原子層沉積成膜技術(ALD)所長的氧化鉿(HfO2)來做為阻擋層。我們使用兩種結構討論對原件所帶來的影響:當我們將氧化鉿層嵌入電洞傳輸層中作為銦離子阻擋層，發現經過長時間的儲存實驗，此種元件結構會帶來更嚴重的劣化;但若將氧化鉿沉積在電動傳輸層與ITO導電玻璃間，卻可以降低原件的衰退，我們將此歸因於養化鉿的保護阻擋了化學反應的發生，並且以X光光電子能譜儀(XPS)的縱深分析圖作為佐證。 因此，本研究所提出的製程及元件結構改良，皆可以成功的應用在異質介面型太陽能電池，並且提升元件之壽命。

This study realizes improvements in the efficiency and stability of bulk-heterojunction polymer solar cells using two approaches: morphological manipulation of the active layer composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM), and elimination of the adverse effects caused by the out-diffusion of the indium tinoxide (ITO) anode. In terms of morphological manipulation, we developed a low-temperature drying process for the active layer that achieved significantly higher power conversion efficiency (PCE) (4.3%) and longer device lifetime (> 1250 h) than those of the standard room-temperature process. The improvements were attributed to the enhanced nucleation of the P3HT crystallites and the restricted large-scale aggregation of the P3HT/PCBM phases at the low drying temperature, which produced a densely interconnected P3HT crystal network that maximized the bulk-heterojunction area and prevented the active layer from morphological shifts with use. In terms of diffusion blocking, we demonstrated that an ultra-thin (0.9 nm) layer of HfO2 deposited by atomic layer deposition (ALD) on the ITO anode effectively eliminated the degradation caused by the out-diffusion of In ions from the anode, while it also improved the PCE of the solar cells. The effectiveness of the ALD HfO2 blocking layer was owing to the excellent surface coverage and low defect density of the ALD films, and the improvement in PCE was due to the raised electrical field by inserted HfO2.