离子液体在有机光电转换器件中的应用研究进展

近年来,离子液体因具有不易挥发、性质稳定、透光性好、导电率高、可设计性,以及易于在界面处形成双电层等物理化学性质,而展现出广阔的应用潜力和前景,逐渐成为国际科学研究的前沿和热点之一。其中,将离子液体应用于染料敏化太阳能电池(Dye-sensitized solar cells,DSSCs)、钙钛矿太阳能电池和有机光电探测器等有机光电转换器件的研究备受关注。 在有机光电转换器件中,离子液体在染料敏化太阳能电池方面的应用最为广泛且完善。高效DSSCs主要是基于有机溶剂的液态电解质结,但有机溶剂在带来较高光电转换效率的同时,其本身存在的易挥发汽化、光热稳定性差等缺点,导致DSSCs的器件寿命与长期稳定性受到影响,离子液体的引入能有效解决以上问题。此外,离子液体还以电子传输层以及界面修饰层的形式引入,具有高电荷迁移率、低功函数以及高稳定性等优点,能在一定程度上改善器件的短路电流、填充因子和光电转换效率等。因此,离子液体成为在DSSCs的实际应用中兼具性价比高、封装难度低、性能好、稳定性高四大优点的辅助材料。在钙钛矿太阳能电池方面,离子液体的低功函数和高电子迁移率以及一些特殊性质如钝化反应、黏度效应等,都能够实现对电子萃取率、电荷转移电阻、钙钛矿结晶情况等方面的控制以满足实际设计要求,进而有助于钙钛矿太阳能电池的光电转换效率、填充因子等性能指标不同程度的提升。在有机光电探测器方面,引入的离子液体能促使在与之接触的界面处形成双电层,双电层的形成及离子液体的高导电率使得入射光不必照射有机光电探测器上下电极的重叠区域仍旧可以产生较大的光电流输出,从而可以有效摆脱有机光电探测器对电极材料透光性要求的局限性。同时双电层的形成还将促进有机光电探测器工作层中的电荷分离,进一步提高有机光电探测器的响应率。 本文主要从染料敏化太阳能电池、钙钛矿太阳能电池、有机光电探测器三个方面,综述了离子液体在有机光电转换器件中的国内外应用研究进展,就离子液体对提升有机光电转换效率及其实现器件新功能的工作机理进行了详细分析,并对其未来的应用研究方向进行了展望,为今后进一步设计出更适合有机光电转换领域应用的离子液体提供参考。

Progress in the Application of Ionic Liquids in Organic PhotoelectricConversion Devices

In recent years, ionic liquids have shown wide application potential and prospects because of their physical and chemical properties, such as non-volatile, stability of properties, favorable transmittance, high conductivity, designability, and easy to form electric double layers at the interface. Accordingly, ionic liquids have gradually become one of the frontier and hot spots in international scientific research. Among them, the applications of ionic liquids in organic optoelectronic conversion devices, including dye-sensitized solar cells, perovskite solar cells and organic photodetectors have attracted numerous attention over the world. In the organic photoelectric conversion devices, the application of ionic liquids in dye-sensitized solar cells is the most extensive and perfect. The high efficiency of dye-sensitized solar cells is primarily depended on liquid electrolyte junctions in organic solvents. Nevertheless, the high photoelectric conversion efficiency benefited from organic solvents is usually accompanied by volatile vaporization, poor photothermal stability, which badly affected the lifetime and long-term stability of dye-sensitized solar cells devices. While the introduction of ionic liquids can effectively solve these problems. In addition, ionic liquids are introduced in the form of electron transport layers and interfacial modification layers, bringing the advantages of high charge mobility, low power function and high stability, which contribute to improving the short-circuit current, filling factor and photoelectric conversion efficiency to a certain extent. As a result, ionic liquids have been recognized as the auxiliary materials with high cost performance ratio, low encapsulation difficulty, excellent performance and good stability in practical application of dye-sensitized solar cells. In perovskite solar cells, the low power function and high electron mobility of ionic liquids and some special properties like passivation reaction, viscosity effect can realize the control of electron extraction rate, charge transfer resistance, perovskite crystallization, so as to meet the design requirements in practice, and further help to improve the photoelectric conversion efficiency and filling factor of perovskite solar cells. Regarding to organic photodetectors, the introduction of ionic liquids can result in the formation of electric double layers at the interface. The formation of electric double layers and the high conductivity of ionic liquids make it possible to produce large photocurrent outputs without the need to illuminate the overlapping region of the upper and lower electrodes of the organic photodetectors. Therefore, it can effectively get rid of the limitation of organic photodetectors on the transmittance of electrode materials, meanwhile, the formation of electric double layers will also promote the charge separation in the working layer of the organic photodetectors, thus further enhance the response rate of the organic photodetectors. In terms of dye-sensitized solar cells, perovskite solar cells and organic photodetectors, this article reviews the research progress in the application of ionic liquids in organic photoelectric conversion devices at home and abroad. The mechanism of ionic liquids for improving the efficiency of organic photoelectronic conversion and realizing the new function of the devices is analyzed and expounded in detail. The future application and research directions of ionic liquids are proposed, for the sake of providing reference for further design of ionic liquids that are more suitable for the application of organic optoelectronic conversion field in the future.