Electroluminescence Generation in PbS Quantum Dot Light-Emitting Field-Effect Transistors with Solid-State Gating

Abstract

The application of light-emitting field-effect transistors (LEFET) is an elegant way of combining electrical switching and light emission in a single device architecture instead of two. This allows for a higher degree of miniaturization and integration in future optoelectronic applications. Here, we report on a LEFET based on lead sulfide quantum dots processed from solution. Our device shows state-of-the-art electronic behavior and emits near-infrared photons with a quantum yield exceeding 1% when cooled. We furthermore show how LEFETs can be used to simultaneously characterize the optical and electrical material properties on the same device and use this benefit to investigate the charge transport through the quantum dot film.

Keywords: field-effect transistors; light emission; low temperature; quantum dots; traps.

Figure 1

QDLEFET device schematics (A) and electroluminescence generation properties. (B) Absorbance and photoluminescence spectra (red and green curves) of an OA-capped PbS CQDs solution, along with the absorbance, photoluminescence, and electroluminescence spectra (violet, blue, and yellow curves, respectively) of a TBAI-treated PbS CQDs thin film. (C) Images of the QDLEFET channel for the gate voltage of −3 V (top) and 4 V (bottom). (D) Position of the recombination area inside the channel as a function of the gate voltage with the width of the Lorentzian peak (red area). (E) Drain current of the QDLEFET and corresponding electroluminescence power versus the gate voltage. (F) Peak energy of the Gaussian-fitted electroluminescence peak and EQE versus the gate voltage.

Figure 2

Output (A) and transfer (B) curves of a QDLEFET. The hysteresis is reported for the curves with the forward and the backward scan illustrated by continuous and dashed curves, respectively. The output curves (A) for the hole channel are plotted in the left and for the electron channel in the right plot. The transfer curves (B) are plotted in exponential (left axis, blue curve) and linear (right axis, orange curve) scale for hole channel (left plot) and electron channel (right plot).

Figure 3

Temperature dependence of the drain current (A) and of the EL EQE (B) versus the gate voltage. Measurements were taken for V_DS = 18 V. The overall drain current decreases at lower temperatures, while the EL EQE increases by 4 orders of magnitude.

Figure 4

(A) Temperature dependence of electron and hole conductivity in the linear regime (blue and orange lines) plotted versusT^–1/3 according to the 2D Mott variable range hopping model. The values, extracted from forward and from reverse hysteresis branches, are shown in open squares and in filled circles, respectively. (B) Electroluminescence quantum efficiency and relative quantum yield for photoluminescence versus temperature. The PL curve is fitted using nearest-neighbor hopping (NNH) at high temperatures and 3D Mott-type variable range hopping (3D-Mott VRH) at low temperatures.

Figure 5

(A) Schematic of the relevant energy levels in the CQD film indicating charge transport (“trans”), transition to hole trap states (“tr”), exciton (the green ellipse), dissociation (“diss”), and exciton radiative/nonradiative recombination (“r” and “nr”). (B) Transfer characteristics of the device at high (180 K) and low temperature (80 K). (C) Electroluminescence peak energy versus gate voltage for the two temperatures as in panel B and (D) EL EQE of QDLEFET for the temperatures as in panel B.