Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter:A Universal Approach Toward High-Performance Blue TADF Top Emission OLED

A novel device structure for thermally activated delayed fluorescence(TADF)top emission organic light-emitting diodes(TEOLEDs)that improves the viewing angle characteristics and reduces the efficiency roll-off is presented.Furthermore,we describe the design and fabrication of a cavity-suppressing electrode(CSE),Ag(12 nm)/WO_(3)(65 nm)/Ag(12 nm)that can be used as a transparent cathode.While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency(EQE)and improved angular dependency than the device fabricated using the microcavity-based Ag electrode,it suffers from low color purity and severe efficiency roll-off.These drawbacks can be reduced by using an optimized multi-quantum well emissive layer(MQW EML).The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE(18.05%),high color purity(full width at half maximum~59 nm),reduced efficiency roll-off(~46%at 1000 cd m^(−2)),and low angular dependence.These improvements can be attributed to the synergistic effect of the CSE and MQW EML.An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence,and the MQW EML effectively confines charges and excitons,thereby improving the color purity and EQE significantly.The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

Manipulation of blue TADF top-emission OLEDs by the first-order optical cavity design:toward a highly pure blue emission and balanced charge transport

The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity displays.Herein,a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices.In addition,by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers,light extraction is increased by nearly 2 times compared to the device without a capping layer.Consequently,the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum,higher maximum current efficiency,and external quantum efficiency compared to the device before optimization.This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.

Electrochemically metal-doped reduced graphene oxide films:Properties and applications

The fine control of doping levels in graphene materials such as reduced graphene oxide(RGO)is important to properly manipulate their ambipolar transport characteristics for various device applications.However,conventional doping methods involve complex chemical reactions,large-scale doping processes,and poor stability.Herein,a simple and controllable electrochemical doping treatment(EDT),performed via the conductive channels created at the RGO surface by the application of an electric field,is introduced to tailor the electrical properties of RGO films.X-ray photoelectron spectroscopy and Raman spectroscopy measurements are performed to detect the presence of Ni atoms in RGO films after the EDT(EDT-RGO).Then,EDT-RGO field-effect transistors(FETs)are fabricated with different doping areas(0 to 100%fractional area)on the RGO active channel to investigate the effect and selective-area doping capability of the EDT.Owing to p-type doping compensation by the intercalated Ni atoms,the electron mobility of the EDT-RGO FET decreases from 1.40 to 0.12 cm2 V-1s-1 compared with that of the undoped RGO-FET,leading to the conversion from ambipolar to unipolar p-type transfer characteristics.