Improved Performance of Organic Light-Emitting Field-Effect Transistors by Interfacial Modification of Hole-Transport Layer/Emission Layer: Incorporating Organic Heterojunctions

Organic heterojunctions (OHJs) consisting of a strong electron acceptor 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) and an electron donor N,N′-di­(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB) were demonstrated for the first time that they can be implemented as effective modification layers between hole transport layer (HTL) and emission layer in the heterostructured organic light-emitting field effect transistors (OLEFETs). The influence of both HAT-CN/NPB junction (npJ) and NPB/HAT-CN junction (pnJ) on the optoelectronic performance of OLEFETs were conscientiously investigated. It is found that both the transport ability of holes and the injection ability of holes into emissive layer can be dramatically improved via the charge transfer of the OHJs and that between HAT-CN and the HTL. Consequently, OLEFETs with pnJ present optimal performance of an external quantum efficiency (EQE) of 3.3% at brightness of 2630 cdm–2 and the ones with npJs show an EQE of 4.7% at brightness of 4620 cdm–2. By further utilizing npn OHJs of HAT-CN/NPB/HAT-CN, superior optoelectronic performance with an EQE of 4.7% at brightness of 8350 cdm–2 and on/off ratio of 1 × 105 is obtained. The results demonstrate the great practicality of implementing OHJs as effective modification layers in heterostructured OLEFETs.