全有机近红外光-可见光上转换近红外成像器件研究

Near-infrared (NIR) imaging has important applications in national economy and military defense. NIR to visible upconversion imaging devices which consists a NIR-photodetector (NIR-PD) integrated with a visible light-emitting diode can transfer NIR signals directly into visible image. Compared with commercial NIR imagers that consist III-V compound semiconductor detectors integrated with Si-based readout integrated circuits have the advantages of compact device structure, small size, low weight, and etc. The disadvantages of complex fabrication process and high cost for inorganic NIR-PDs have to be faced in both all inorganic and organic/inorganic hybrid upconvertors. These disadvantages can be ignored in all organic upconvertors. However, there are few reports about these all organic upconvertors and the conversion efficiencies are still lower for practical applications. These were attributed to the fact that low efficient organic NIR-PDs (NIR-OPD) and organic light-emitting diodes (OLEDs) were adopted in the integrated devices and the connection unit has never been optimized. Thermally actived delayed fluorescence (TADF)-OLED is a new type OLED technology and has the advantages of high efficiency for phosphorescent OLEDs and low turn-on voltage for fluorescent OLEDs. Based on our previous results in NIR-OPDs and TADF-OLEDs, in this project we will construct all organic upconversion NIR imaging devices by integrating a NIR-OPD with a TADF-OLED. The goal of this project is to obtain high performance all organic upconversion NIR imaging devices through optimizing the materials and device structures of the individual NIR-OPD and TADF-OLED and carefully manipulating the properties of the connection unit between these two devices.

近红外成像技术在国民经济和军事国防方面具有重要应用。由近红外光探测器集成可见光发光二极管构筑的上转换近红外成像器件可直接将近红外光信号转换成可见光影像。与传统的Ⅲ-Ⅴ族半导体探测器集成Si基读出电路构成的器件相比，具有结构紧凑、体积小、重量轻等优点。全无机或有机/无机复合上转换近红外成像器件无法避免无机近红外光探测器制备时所面临的工艺复杂、成本高的缺点。全有机上转换近红外成像器件可克服以上缺点，但目前报道较少，转换效率较低。其原因为所使用的有机近红外光探测器和有机发光二极管（OLED）效率较低，且二者连接界面未经优化。热激活延迟荧光是一种新型的OLED技术，兼备了磷光OLED的高效率和荧光OLED的低开启电压的优点。在课题组前期有机近红外光探测器与热激活延迟荧光OLED研究基础上，本项目拟将二者集成，通过材料和单元器件结构的优化及二者连接界面的调控，获得高效全有机上转换近红外成像器件。

近红外成像技术在国民经济和军事国防方面具有重要应用。由近红外光探测器集成可见光发光二极管构筑的上转换近红外成像器件可直接将近红外光信号转换成可见光影像。全有机上转换成像器件具有工艺简单、成本低、可使用柔性基板等优点。但是目前全有机上转换近红外成像器件报道较少，转换效率较低。其原因为所使用的有机近红外光探测器和有机发光二极管（OLED）效率较低，且二者连接界面未经优化。本项目在热活化延迟荧光（TADF）OLED和有机近红外光探测器单元器件材料和结构的优化的基础上，将二者进行集成，获得高性能全有机上转换近红外成像器件。通过项目研究，获得主要成果如下：（1）通过优化器件结构，获得基于TAPC和T2T的分子间电荷转移态的绿光TADF-OLED，其EQE达到11.6%；进一步物理机制研究表明，器件的效率主要由发光层的PL量子效率决定，器件的载流子平衡系数在一定程度上影响器件的效率；器件高电流密度下的效率滚降由发光层的PL寿命和器件的载流子平衡系数共同决定。采用n型PbI2作为阳极界面层，提高了基于TCTA和PO-T2T的分子间电荷转移态的绿光TADF-OLED的效率。通过优化电子传输层，获得了基于2PXZ-OXD的分子内电荷转移态的非掺杂绿光TADF-OLED，其EQE达到11.9%。（2）采用n型PbI2作为阳极界面层，提高了基于PbPc的近红外光探测器的效率；采用SubPc作为电子受体材料构筑了有机近红外光探测器；利用PbPc薄膜中缺陷态，制备了具有光电倍增效应的有机近红外光探测器。（3）将上述绿光TADF-OLED和光电倍增型有机近红外光探测进行集成，通过优化器件结构，获得了近红外光-绿光上转换发光器件，其光子对光子上转换效率高达256%，为目前同类器件最高值，相关成果以封底文章的形式发表在J. Phys. Chem. Lett.上。本项目研究成果共发表SCI论文19篇，其中影响因子大于3的论文16篇。