基于电荷产生层的高性能有机发光晶体管研究

Organic light-emitting transistors (OLETs) are a novel class of optoelectronic devices that combine the electrical switching functionality of organic field-effect transistors (OFETs) and the capability of light generation of organic light-emitting diodes (OLEDs), which also show high current density and low absorption loss. These advantages enable them superior for wide applications, especially for flexible displays and electrically pumped organic laser diodes. However, due to the strict requirements for the carrier mobility, photoluminescence quantum yield and energy level alignment, the kinds of materials available for high performance devices are so limited. It results in inefficient carrier injection and transportation, unbalance between electrons and holes, low exciton yield, and finally greatly limits the performance of the devices. This project proposes for the first time to incorporate a charge generation layer (CGL) between the organic interfaces of the devices. The CGL can bring extra carriers, balance the transportation and recombination between the electrons and holes, which will promote the performances of the devices. Meanwhile, the bending of the energy levels resulted from the charge transfer between the CGL and the organic layers may meet the strict requirement of the energy level for the organic heterojunction structure, which would ensure more kinds of organic semiconductors with higher carrier mobility to be available. The research results from this project will lay solid foundation for OLETs to be used in flexible displays as well as electrically pumped organic laser diodes.

由于兼具有机场效应晶体管的电开关功能和有机发光二极管的电致发光功能、高电流密度、低吸收损耗等特点，有机发光晶体管（OLETs）在柔性显示和实现电泵浦有机激光器等方面展现出突出优势，成为一种备受关注的新型有机光电子器件。但由于对材料载流子迁移率、荧光量子效率和能级匹配等要求严格，导致目前 OLETs可选材料非常稀缺，载流子注入和传输水平有限，电子和空穴难以实现平衡高效传输，激子的产生效率低下，最终极大的限制了器件性能的提升。本项目首次提出在OLETs的有机层/有机层界面引入电荷产生层，以提供额外的载流子、平衡电子和空穴的传输与复合，提升器件的发光性能；通过电荷产生层与有机层之间电荷转移形成的能级弯曲，满足异质结结构对能级匹配的苛刻要求，使高载流子迁移率有机半导体材料能够得以应用。研究结果将为OLETs在柔性显示和实现电泵浦有机激光器等方面的应用打下基础。

有机发光场效应晶体管（OLEFETs）由于集成的发光与电开关功能，在显示、集成光互连以及电泵浦有机激光方面展现出重要的应用前景，近年来吸引了人们越来越多的研究兴趣。由于器件特殊的载流子水平传输特征，有机材料低的载流子迁移率以及不平衡的载流子注入与传输成为制约OLEFETs发光性能的突出因素。本项目首次提出在多层OLEFETs中引入电荷产生层，分别构筑了金属氧化物型以及有机异质结型电荷产生层，均大幅改善了器件的载流子传输水平和平衡性，使器件获得了优异的光电特性。进一步的研究表明，器件性能改善的机理可归因于n型有机半导体或金属氧化物与p型有机半导体材料之间的电荷转移，该电荷转移使得空穴浓度大幅提升，同时有利于空穴向发光层的注入以及漏极处电子的注入。在此基础上，我们还首次采用热活化延迟荧光（TADF）材料作为OLEFETs的发光层，获得了在高亮度下外量子效率优于相同结构的OLED的器件性能。同时，还构建了基于电荷产生层结构OLEFETs的新型近红外-可见光上转换器件，获得了~7%的光-光效率，为当前全有机上转换器件的最好结果，展现了OLEFETs在构建低成本、柔性、便携式有机上转换器件方面的重要潜力。在本项目的支持下，共发表SCI论文8篇。