基于梯度结构空穴注入层的高效率紫外有机发光器件研究

The research topic of organic light-emitting device extends from visible to near ultraviolet range. The highest occupied molecular orbit (HOMO) level of ultraviolet organic light-emitting material doesn’t match with the work function of indium-tin-oxide (ITO) anode, the hole-injection barrier-height is as high as 2 eV, which results in poor hole-electron balance and counteracts the enhancement of luminous efficiency. It is considered as the bottleneck of restricting performance improvement in ultraviolet organic light-emitting device. Meanwhile, the excimer forming and distributing zone is not easily controlled as a result of the lack of blocking layer with higher HOMO level, which results in unfavorable electroluminescent spectra. In this project, we avoid employing the existing research ideas of conventional hole-injection layer and excimer blocking. We propose incorporating graded hole-injection layer between ITO anode and organic layer based on the theory of carrier balance and interface engineering. Investigating the design and fabrication of efficient and controllable graded hole-injection layer, realizing effective hole injection, and thereby improving hole-electron balance. The interface characteristics of graded hole-injection layer are investigated by using impedance spectroscopy, in situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The carriers transporting and excimer distribution characteristics is adjusted based on the distribution and amounts of injected holes in the organics. Furthermore, the related mechanism of interface characteristics and excimer adjustment is clarified. We provide a novel approach for constructing efficient ultraviolet organic light-emitting device and basic theory study of solid-state lightings.

有机发光器件的研究热潮从可见光波段延伸至近紫外，紫外有机发光材料的HOMO能级与ITO阳极的功函数不匹配，空穴注入势垒高达2 eV，导致空穴-电子平衡性差，限制了发光效率的提高，成为制约紫外有机发光器件性能的瓶颈。同时，缺乏HOMO能级更高的阻挡层导致激子形成和移动区域不易控制，器件光谱特性不理想。本项目跳出常规空穴注入层和阻挡限定激子区域的现有研究思路和方法，基于电荷平衡和界面调控原理，在紫外有机发光器件的“ITO/有机层”之间引入梯度结构空穴注入层，研究高效、可控的梯度结构空穴注入层的设计及其构筑方法，实现空穴的高效注入，改善载流子平衡性。进一步采用阻抗谱和原位XPS（UPS）对梯度结构空穴注入层的界面特性开展研究，探索空穴注入到有机材料中的数量及其分布，据此调控载流子输运特性和激子分布特征，阐明界面特性和激子调控的相关机理，为高效率紫外有机发光器件及固体发光基础理论研究提供新思路。

紫外有机发光器件在荧光检测、信息存储、激发光源等领域中具有潜在应用前景，同时器件响应速度快、柔性好、超薄便携等独特优势成为当前有机发光领域的研究热点。紫外有机发光材料的带隙较宽，其HOMO能级与普遍使用的ITO阳极功函数不匹配，空穴注入势垒高达2 eV，导致空穴难以注入到发光层中，空穴-电子平衡性差，限制了发光效率的提高，成为制约紫外有机发光器件性能的瓶颈。同时，缺乏HOMO能级更高的阻挡层导致紫外发光层中激子的形成区域不易控制，光谱特性不理想。项目基于电荷平衡和界面调控原理，在紫外有机发光器件的“ITO/有机层”之间引入梯度结构空穴注入层以期获得高效率。通过一系列实验和理论研究，设计并制备了具有梯度能级结构的双层空穴注入层（如GO/MoOx、PEDOT:PSS/MoOx）、合成了金属氧化物（如La2O3、GeO2、MoOx、WOx、VOx）和新型二维材料（如CNxHy、MoS2）作为空穴注入层或p型掺杂剂、制备了p型掺杂的复合空穴注入层。采用AFM、SEM、XRD、SEM、Ramman、PL、XPS、UPS、阻抗谱等表征手段对空穴注入层和界面特性进行了表征分析，详细研究了空穴注入层的能级结构、空穴注入特性及其调控措施。并阐明了载流子注入、传输、平衡、激子形成区域调控的相关机理，为高性能紫外有机发光器件提供了指导。所制备的紫外有机发光器件最优性能为：发光峰377 nm，半峰宽35 nm，辐照度达到14.2 mW/cm2，外量子效率高达4.6%，是目前报道的波长小于400nm紫外有机发光器件的最高水平。项目研究成果在Journal of Materials Chemistry C、Organic Electronics、Applied Physics Letters、发光学报等期刊发表学术论文31篇，其中SCI收录28篇；申请专利9项，其中授权发明专利3项；培养5名硕士研究生毕业。项目研究成果在相关学术会议和学术交流活动中以邀请报告、分组汇报、墙报展示等进行了介绍。本项目对于构筑高效率紫外有机发光器件的理论研究和实践应用具有十分重要的学术价值和现实意义，为多层结构光电子器件的界面特性评价等基础理论研究提供了参考。