High Performance p‐ and n‐Type Light‐Emitting Field‐Effect Transistors Employing Thermally Activated Delayed Fluorescence. (21st May 2018)

• Record Type: Journal Article
• Authors: Sobus, Jan; Bencheikh, Fatima; Mamada, Masashi; Wawrzinek, Robert; Ribierre, Jean‐Charles; Adachi, Chihaya; Lo, Shih‐Chun; Namdas, Ebinazar B.
• Is Part Of: Advanced functional materials. Volume 28:Number 28(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-05-21
• Subjects: benzothiophene -- light‐emitting field‐effect transistors -- organic electronics -- thermally activated delayed fluorescence -- zinc‐tin oxide; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.201800340
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: Light‐emitting field‐effect transistors (LEFETs) are an emerging type of devices that combine light‐emitting properties with logical switching function. One of the factors limiting their efficiency stems from the spin statistics of electrically generated excitons. Only 25% of them, short lived singlet states, are capable of light emission, with the other 75% being long lived triplet states that are wasted as heat due to spin‐forbidden processes. Traditionally, the way to overcome this limitation is to use phosphorescent materials as additional emission channel harnessing the triplet excitons. Here, an alternative strategy for triplet usage in LEFETs in the form of thermally activated delayed fluorescence (TADF) is presented. Devices employing a TADF capable material, 4CzIPN (2, 4, 5, 6‐tetra[9H‐carbazol‐9‐yl]isophthalonitrile), in both n‐type and p‐type configurations are shown. They manifest excellent electrical characteristics, consistent brightness in the range of 100–1, 000 cd m ‐2 and external quantum efficiency (EQE) of up to 0.1%, which is comparable to the equivalent organic light‐emitting diode (OLED) based on the same materials. Simulation identifies the poor light out‐coupling as the main reason for lower than expected EQEs. Transmission measurements show it can be partially alleviated using a more transparent top contact, however more structural optimization is needed to tap the full potential of the device. Abstract : Light‐emitting field‐effect transistors (LEFETs) are a novel class of optoelectronic devices combining switching and light emission properties in a single material stack. The first p‐type and n‐type LEFETs employing thermally activated delayed fluorescence organic material are successfully built. Experimental data are supported by numerical simulation, leading to proper localization of the recombination zone and identification of loss pathways.