Very Bright and Efficient Microcavity Top-Emitting Quantum Dot Light-Emitting Diodes with Ag Electrodes.
The microcavity effect in top-emitting quantum dot light-emitting diodes (TQLEDs) is theoretically and experimentally investigated. By carefully optimizing the cavity length, the thickness of the top Ag electrode and the thickness of the capping layer, very bright and efficient TQLEDs with external quantum efficiency (EQE) of 12.5% are demonstrated. Strong dependence of luminance and efficiency on cavity length is observed, in good agreement with theoretical calculation. By setting the normal-direction resonant wavelength around the peak wavelength of the intrinsic emission, highest luminance of 112 000 cd/m(2) (at a driving voltage of 7 V) and maximum current efficiency of 27.8 cd/A are achieved, representing a 12-fold and a 2.1-fold enhancement compared to 9000 cd/m(2) and 13.2 cd/A of the conventional bottom emitting devices, respectively, whereas the highest EQE of 12.5% is obtained by setting the resonant wavelength 30 nm longer than the peak wavelength of the intrinsic emission. Benefit from the very narrow spectrum of QDs and the low absorption of silver electrodes, the potential of microcavity effect can be fully exploited in TQLEDs.
Department of Electrical and Electronic Engineering, Southern University of Science and Technology , Shenzhen 518055, P. R. China.|State Key Lab of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-sen University , Guangzhou 510275, P. R. China.
Guohong
G
Liu
State Key Lab of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-sen University , Guangzhou 510275, P. R. China.
Xiang
X
Zhou
Department of Electrical and Electronic Engineering, Southern University of Science and Technology , Shenzhen 518055, P. R. China.
Shuming
S
Chen
light-emitting diodes; microcavity effect; quantum dot; silver electrodes; top-emitting structures