Quantum-dot and organic hybrid tandem light-emitting diodes with multi-functionality of full-color-tunability and white-light-emission

Abstract

Realizing of full-color quantum-dot LED display remains a challenge because of the poor stability of the blue quantum-dot and the immature inkjet-printing color patterning technology. Here, we develop a multifunctional tandem LED by stacking a yellow quantum-dot LED with a blue organic LED using an indium-zinc oxide intermediate connecting electrode. Under parallel connection and alternate-current driving, the tandem LED is full-color-tunable, which can emit red, green and blue primary colors as well as arbitrary colors that cover a 63% National Television System Committee color triangle. Under series connection and direct current driving, the tandem LED can emit efficient white light with a high brightness of 107000 cd m^-2 and a maximum external quantum efficiency up to 26.02%. The demonstrated hybrid tandem LED, with multi-functionality of full-color-tunability and white light-emission, could find potential applications in both full-color-display and solid-state-lighting.

Fig. 1. Device structure and driving methods of the multifunctional LED.

a Schematic device structure of the multifunctional tandem LED with an extractable IZO intermediate electrode. The Y-QLED and B-OLED can be connected either in parallel or in series. Under parallel connection and AC driving, a color-tunable device is achieved. Under series connection and DC driving, a white-emitting device is obtained. b Energy level alignment of the multifunctional tandem LED.

Fig. 2. Mechanism and driving methods of full-color-tunable LED.

a Schematic diagram of the charge injection and recombination trajectory of the Y-QLED. The recombination zone is gradually migrated from R-QDs to G-QDs when the driving voltage is increased, and thus the emission color of Y-QLED can be controlled by the voltage. b The CIE chart, CIE coordinates, and photos; c the AC driving signals; and d the emission spectra of a color-tunable device that emits different colors. The color can be continuously tuned from (I) R to G, (II) B to R, (III) B to O, and (IV) B to G.

Fig. 3. Performance of the full-color-tunable LED.

a The EQE–J, b J–V–L, and c EQE–L characteristics of B-OLED and Y-QLED, measured by extracting the IZO as a common electrode. d CIE chart and color coordinates of the R, G, and B primary colors. By degrading the color gamut from 63% to 45% NTSC, a wide range of brightness for the R, G, and B emission can be obtained.

Fig. 4. Performance of the tandem white LED.

a The J–V–L, b EQE–J characteristics of the B-OLED, Y-QLED, and tandem white LED. c The photos of an operating tandem white LED driven by different voltage levels. d Normalized emission spectra of the tandem white LED under d DC driving, and e, f AC driving. g CIE coordinates of the white LED (star), B-OLED (blue point), and Y-QLED (red point). Under AC driving, stable white emission with CIE coordinates fixed at (0.34, 0.36) can be obtained for a wide range of brightness (1000–50,000 cd m⁻²). Also, the color temperature can be tuned from 1500 to 10,000 K, which well traces the blackbody locus. h AC signals and i DR–L and V_B–L curves for driving a color stable white LED.