Browsing by Author "Wu, Hung-Bao"

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Efficient and color-stable solid-state white light-emitting electrochemical cells employing red color conversion layers
(2012-03-01)
Wu, Hung-Bao
;
Chen, Hsiao-Fan
;
Liao, Chih-Teng
;
Su, Hai-Ching
;
Wong, Ken-Tsung
We report efficient and color-stable white light-emitting electrochemical cells (LECs) by combining single-layered blue-emitting LECs with red-emitting color conversion layers (CCLs) on the inverse side of the glass substrate. By judicious choosing of the red-emitting dye doped in CCLs, good spectral overlap between the absorption spectrum of the red-emitting dye and the emission spectrum of the blue-emitting emissive material results in efficient energy transfer and thus sufficient down-converted red emission at low doping concentrations of the red-emitting dye in the CCLs. Low doping concentration is beneficial in reducing self-quenching of the red-emitting dye, rendering efficient red emission. Electroluminescent (EL) measurements show that the peak external quantum efficiency and the peak power efficiency of the white LECs employing red CCLs reach 5.93% and 15.34 lmW (1), respectively, which are among the highest reported for white LECs. Furthermore, these devices exhibit bias-insensitive white EL spectra, which are required for practical applications, due to nondoped emissive layers. These results reveal that single-layered blue-emitting LECs combined with red-emitting CCLs are one of the potential candidates for efficient and color-stable white light-emitting devices. (C) 2011 Elsevier B. V. All rights reserved.
Improving device efficiencies of solid-state white light-emitting electrochemical cells by adjusting the emissive-layer thickness
(2013-10-01)
Jhang, Yuan-Pei
;
Chen, Hsiao-Fan
;
Wu, Hung-Bao
;
Yeh, Yun-Shiuan
;
Su, Hai-Ching
Exciton quenching in the recombination zone close to electrochemically doped regions would be one of the bottlenecks for improving device efficiencies of solid-state white light-emitting electrochemical cells (LECs). To further enhance device efficiencies of white LECs for practical applications, we adjust the emissive-layer thickness to reduce exciton quenching. In white LECs with properly thickened emissive-layer thickness, the recombination zone can be situated near the center of the emissive layer, rendering mitigated exciton quenching and thus enhanced device efficiencies. High external quantum efficiencies and power efficiencies of optimized devices reach ca. 11% and 20 lm/W, respectively, which are among the highest reported for white LECs. These results confirm that tailoring the thickness of the emissive layer to avoid exciton quenching would be a feasible approach to improve device efficiencies of white LECs. (C) 2013 Elsevier B.V. All rights reserved.