摻雜不同烷基長度之離子性鹽類以改善有機電化學發光元件之載子平衡

Abstract

近年來固態電化學發光元件因具有低操作電壓、簡單的元件結構與良好的載子注入能力等優點，而備受矚目。離子性鹽類經常摻雜於電化學發光元件的主動層中，提供額外的離子以增快元件的反應速度。除了元件的離子特性之外，元件的載子平衡也會受摻雜的離子性鹽類影響而有所改變。在這項研究中，我們透過在電化學發光元件中摻雜不同烷基碳鏈長度的咪唑(imidazole)基離子性鹽類，提升了元件的亮度與外部量子效率。隨著摻雜鹽類的烷基碳鏈長度變長，有著元件電流密度下降，以及複合區位置更靠近陽極的趨勢。這些結果顯示隨著摻雜鹽類體積的增加，對主動層中電洞遷移率的衰減大於電子遷移率。當選用體積適當的鹽類摻雜時，改善了元件的載子平衡，元件效率可提升至未摻雜元件的近兩倍。這項研究展現了改善元件效率的可行策略，並對鹽類體積影響電化學發光元件載子平衡的物理機制有著深入的探討。

Recently, solid-state light-emitting electrochemical cells (LECs) have attracted much attention since they have advantages such as low operation voltages, simple device structure and balanced carrier injection. Salts are commonly added in the emissive layer of LECs to provide additional mobile ions and thus to accelerate device response. However, in addition to modified ionic property, carrier balance of LECs would also be tailored by salt additives. In this work, we improve brightness and efficiency of LECs by incorporating imidazole-based salts bearing various alkyl chain lengths. As the alkyl chain length of the added salt increases, the device current decreases and the recombination zone approaches the anode. These results reveal that hole transport in the emissive layer of LEC containing a salt with a larger size would be impeded more significantly than electron transport. When doped with a salt possessing a proper size, nearly doubled device efficiency as compared to that of the neat-film device can be obtained due to improved carrier balance. This work demonstrates a feasible strategy to improve device performance of LECs and clarifies the physical insights of the effect of salt size on carrier balance of LECs.