Abstract
Light-emitting field effect transistors (LEFETs) are an emerging class of multifunctional optoelectronic devices. It combines the light emitting function of an OLED with the switching function of a transistor in a single device architecture. The dual functionality of LEFETs has the potential applications in active matrix displays. However, the key problem of existing LEFETs thus far has been their low EQEs at high brightness, poor ON/OFF and poorly defined light emitting area - a thin emissive zone at the edge of the electrodes. Here we report heterostructure LEFETs based on solution processed unipolar charge transport and an emissive polymer that have an EQE of up to 1% at a brightness of 1350 cd/m2, ON/OFF ratio > 104 and a well-defined light emitting zone suitable for display pixel design. We show that a non-planar hole-injecting electrode combined with a semi-transparent electron-injecting electrode enables to achieve high EQE at high brightness and high ON/OFF ratio. Furthermore, we demonstrate that heterostructure LEFETs have a better frequency response (fcut-off = 2.6 kHz) compared to single layer LEFETs. The results presented here therefore are a major step along the pathway towards the realization of LEFETs for display applications.
Highlights
Defining the light emitting area for displays in the unipolar regime of highly efficient light emitting transistors
We demonstrate that heterostructure Light-emitting field effect transistors (LEFETs) have a better frequency response compared to single layer LEFETs
In order to employ LEFETs for display applications, certain prerequisites must be achieved including: (i) high external quantum efficiency (EQE) at high brightness; (ii) low off current to reduce power dissipation in the device; (iii) high switching capability (ON/OFF ratio); (iv) acceptable temporal response (,5 kHz being acceptable)[8]; and (v) a well-defined and spatially stable light emitting area with a sufficient aperture ratio for pixel design
Summary
We report unipolar LEFETs based on solution processed charge transport and emissive polymers with an EQE of up to 1% at a brightness of 1350 cd/m2, with a well-defined light-emitting zone suitable for display pixel design. In the case of the PBTTT/SY bilayer LEFETs using the parameter set L 5 100 mm, Vds 5 150 V, and f23dB 5 2.6 kHz, we obtain a PBTTT FET mobility of 3 3 1023 cm2/ Vs, which is again in agreement with measured steady-state mobility These results suggest that the cut-off frequency for the Pix-LET devices is independent of the emissive layer and mainly dependent on the charge transport material and the channel length. The results are a significant advance towards the ultimate goal of solution processed LEFETs and printed organic semiconductors for display applications
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