Efficient and bright polymer light emitting field effect transistors Mujeeb Ullah a , Kristen Tandy a , Soniya D. Yambem a , Khalid Muhieddine a , Wen Jie Ong b , Zugui Shi b , Paul L. Burn a , Paul Meredith a , Jun Li b,⇑ , Ebinazar B. Namdas a,⇑ a Centre for Organic Photonics & Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia b The Institute of Materials Research and Engineering, Singapore article info Article history: Received 2 July 2014 Received in revised form 16 October 2014 Accepted 11 December 2014 Available online 23 December 2014 Keywords: OTFT Light emitting transistors OLED Display abstract Light emitting field effect transistors (LEFETs) are emerging as a multi-functional class of optoelectronic devices. LEFETs can simultaneously execute light emission and the standard logic functions of a transistor in a single architecture. However, current LEFET architectures deliver either high brightness or high efficiency but not both concurrently, thus limiting their use in technological applications. Here we show an LEFET device strategy that simul- taneously improves brightness and efficiency. The key step change in LEFET performance arises from the bottom gate top-contact device architecture in which the source/drain elec- trodes are semitransparent and the active channel contains a bi-layer comprising of a high mobility charge-transporting polymer, and a yellow–green emissive polymer. A record external quantum efficiency (EQE) of 2.1% at 1000 cd/m 2 is demonstrated for polymer based bilayer LEFETs. Ó 2014 Elsevier B.V. All rights reserved. Organic semiconducting polymers exhibit novel physical, electrical and optical properties. Many of these properties such as the ability for large area solution pro- cessing, plus the almost unlimited possibilities with respect to molecular design and engineering are not typi- cally available in conventional inorganic semiconductors such as silicon and germanium [1]. As a result, a number of new applications have emerged that are enabled by this class of materials. In particular, organic field effect transis- tors (OFETs) [2–5] and organic light emitting diodes (OLEDs) [5–9] are of importance because of their potential for wide spread use in flexible and wearable electronics. More recently, light emitting field effect transistors (LEFETs) have been developed and are of significant inter- est because they offer the combined advantages of both OFETs and OLEDs but in a single device architecture [10–24]. This dual functionality has potential in a number of new applications such as simplified pixels for flat panel displays [11,12], as integrated optoelectronic devices [13,14], sensors, and even electrically driven lasers [15,16]. Despite significant recent progress, the combined optical and electrical performance of LEFETs is yet to reach the level necessary for technological up-take. In most current LEFET architectures there is a trade-off between efficiency, brightness, and FET characteristics. To achieve simultaneous high-performance for both the electrical and light emission properties, certain prerequi- sites, including high charge mobility, balanced carrier transport, high photoluminescence quantum yield, as well as efficient recombination are needed. However, to date, there has been limited success in achieving these prerequi- sites at a functional level. Over the past decade, several device strategies to improve performance such as single layer [10,17,18], bi-layer [19,20], multilayer [21–23] and http://dx.doi.org/10.1016/j.orgel.2014.12.014 1566-1199/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. E-mail addresses: j-li@imre.a-star.edu.sg (J. Li), e.namdas@uq.edu.au (E.B. Namdas). Organic Electronics 17 (2015) 371–376 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel