Recent Developments and Novel Applications of Thin Film, Light‐Emitting Transistors

Abstract

Light-emitting field-effect transistors (LEFETs) combine switching and amplification with light emission and thus represent an interesting optoelectronic device. They are not limited anymore to a few examples and specific materials but are nearly universal for a wide range of semiconductors, from organic to inorganic and nanoscale. This review introduces the basic working principles of lateral unipolar and ambipolar LEFETs and discusses recent examples based on various solution-processed semiconducting materials. Applications beyond simple light emission are presented and possible future directions for lightemitting transistors with added functionalities are outlined. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201905269.thus excluding vertical LEFETs, which have been demonstrated for some organic emitter systems. [5][6][7] We will start with LEFETs that do not rely on the injection of both holes and electrons in a single semiconducting layer but show unipolar charge transport and may include multiple semiconducting layers. This short section will be followed by an overview of truly ambipolar single-layer LEFETs, the different possible working principles and various emissive semiconductors with their advantages and drawbacks. The review will conclude with recent examples of LEFET applications that go beyond simple light-emission and take advantage of specific device properties to add functionalities that are difficult to achieve with other optoelectronic devices.

Recent Advances in Multi‐Layer Light‐Emitting Heterostructure Transistors

“…These small molecular emitters have also been commonly integrated with p‐type organic semiconductors, including 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT‐C8) and pentacene, to achieve high efficiency multi‐layer LETs. [ 30,34,35 ]…”

“…Moreover, due to the balanced injection/transport of carriers, the recombination of holes and electrons can be more efficiently controlled to be in the channel area, which can further increase the OLET optoelectronic performances. [ 30,64,77 ] In the early research stage, p‐type organic and an n‐type inorganic (or metal oxide) semiconductors were vertically stacked to achieve ambipolarity. [ 41,42,70–72,75 ] For example, Dinelli et al.…”

“…The resulting multi‐layer LETs have a channel with as many as several semiconductors to form heterostructures, including hole/electron charge injection layers, hole/electron charge transporting layers, and a charge recombination light‐emitting layer (EML). [ 29,30 ] Therefore, separation of charge transport processes and light emission enables the adoption of the best semiconductor for each of the tasks, thus significantly broadening the material selection options. As a consequence, combined with optimization of LET device architecture, LETs with enhanced optoelectronic performance more suitable for applications as demanding as in active matrix displays have been realized.…”

“…More recently, Simon et al. [ 36 ] reported the development of QD based LETs and Zaumseil [ 30 ] introduced the latest LET applications. In this review, we specifically and systematically summarize the development of multi‐layer heterostructure LETs.…”

Improving the Efficiency of Multilayer Organic Light‐Emitting Transistors by Exploring the Hole Blocking Effect

“…Organic light‐emitting transistors (OLETs) have gained wide attention due to their integrated switching function of field‐effect transistors and luminescence function of organic light‐emitting devices (OLEDs), which enable them fascinating applications in the fields of flat panel displays, optical communication, sensors, and potentially, electrically driven organic lasers. [ 1,2 ] During the past decade, great efforts have been made to improve the performance of the OLETs. For instance, various organic materials with high carrier mobilities, [ 3–6 ] high photoluminescence quantum yield (PLQY), [ 7–9 ] and exciton utility efficiency [ 10–13 ] have been adopted or developed; different device structures [ 14,15 ] and interfacial/surface modification strategies [ 16,17 ] facilitating the injection/transport of carriers have also been investigated.…”