Browsing by Author "Cheng, Chia-Yu"

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Efficient solid-state white light-emitting electrochemical cells employing embedded red color conversion layers
(2015-01-01)
Lu, Jung-Sheng
;
Chen, Hsiao-Fan
;
Kuo, Jung-Chin
;
Sun, Ray
;
Cheng, Chia-Yu
Recently, white light-emitting electrochemical cells (LECs) have attracted scientific attention due to their advantages of simple device structure, low operation voltage and compatibility with solution processes. In this work, efficient white emission from blue-emitting LECs with embedded red color conversion layers (CCLs) is reported. The red CCL is embedded between an indium tin oxide (ITO) layer and a glass substrate. The blue electroluminescence (EL) trapped in the waveguided mode, i.e. in the ITO layer, shows an evanescent tail in the CCL layer and excites the red-emitting dye, generating red photoluminescence (PL). Because the trapped blue EL can be partially transferred to the out-coupled red PL, the doping concentration of the red dye in the CCL can be reduced, and thus the absorption loss of the blue EL in the forward direction (air mode) can be mitigated, rendering enhanced device efficiency. The peak external quantum efficiency and power efficiency obtained in the blue-emitting LECs with embedded red CCLs are up to 12.5% and 27 lm W-1, respectively. These values are among the highest reported for white LECs, and thus confirm that blue-emitting LECs containing embedded red CCLs are capable of providing efficient white emission.
Enhancing device efficiencies of solid-state near-infrared light-emitting electrochemical cells by employing a tandem device structure
(2014-03-01)
Lee, Chia-Lin
;
Cheng, Chia-Yu
;
Su, Hai-Ching
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Compared to near-infrared (NIR) organic light-emitting devices, solid-state NIR light-emitting electrochemical cells (LECs) could possess several superior advantages such as simple device structure, low operating voltages and balanced carrier injection. However, intrinsically lower luminescent efficiencies of NIR dyes and self-quenching of excitons in neat-film emissive layers limit device efficiencies of NIR LECs. In this work, we demonstrate a tandem device structure to enhance device efficiencies of phosphorescent sensitized fluorescent NIR LECs. The emissive layers, which are composed of a phosphorescent host and a fluorescent guest to harvest both singlet and triplet excitons of host, are connected vertically via a thin transporting layer, rendering multiplied light outputs. Output electro-luminescence (EL) spectra of the tandem NIR LECs are shown to change as the thickness of emissive layer varies due to altered microcavity effect. By fitting the output EL spectra to the simulated model concerning microcavity effect, the stabilized recombination zones of the thicker tandem devices are estimated to be located away from the doped layers. Therefore, exciton quenching near doped layers mitigates and longer device lifetimes can be achieved in the thicker tandem devices. The peak external quantum efficiencies obtained in these tandem NIR LECs were up to 2.75%, which is over tripled enhancement as compare to previously reported NIR LECs based on the same NIR dye. These efficiencies are among the highest reported for NIR LECs and confirm that phosphorescent sensitized fluoresce combined with a tandem device structure would be useful for realizing highly efficient NIR LECs. (C) 2014 Elsevier B. V. All rights reserved.
Enhancing device efficiencies of solid-state white light-emitting electrochemical cells by employing waveguide coupling
(2015-01-01)
Cheng, Chia-Yu
;
Wang, Chi-Wei
;
Cheng, Jing-Rong
;
Chen, Hsiao-Fan
;
Yeh, Yun-Shiuan
Solid-state white light-emitting electrochemical cells (LECs) have received intense scientific attention owing to their potential applications in display and lighting. Although device efficiencies of white LECs have been significantly improved in recent years, further improvements are still required for their practical applications. In this work, we demonstrate the enhancement of device efficiencies of white LECs by employing waveguide coupling. Two transparent photoresist (TPR) layers doped with TiO2 nanoparticles (NPs) are inserted between the indium tin oxide (ITO) layer and the glass substrate. By tuning the doping concentration of 25 nm TiO2 NPs in the upper TPR layer to adjust the refractive index, effective waveguide coupling between the ITO layer and the lower TPR layer can be achieved. Since the lower TPR layer contains 250 nm TiO2 NPs, electroluminescence (EL) outcoupled from the ITO layer can be scattered and redirected into the forward direction. Furthermore, the EL trapped in the glass substrate can also transmit into the lower TPR layer and then is scattered to the forward direction. When the EL trapped in the ITO layer and the glass substrate can be effectively recycled into the forward direction, the peak external quantum efficiency and power efficiency obtained in white LECs employing waveguide coupling are up to 19.4% and 34.1 lm W-1, respectively. These efficiencies are among the highest reported for white LECs and thus confirm that waveguide coupling would be useful for realizing highly efficient white LECs. In addition to the enhanced device efficiencies, improved color migration of EL spectra, which is desired for lighting applications, can be obtained in white LECs with scattering waveguide layers since EL of different angles can be mixed in the forward direction.
Non-doped solid-state white light-emitting electrochemical cells employing the microcavity effect
(2015-03-14)
Lin, Guan-Rung
;
Chen, Hsiao-Fan
;
Shih, Hsien-Chang
;
Hsu, Jia-Hong
;
Chang, Yi
Solid-state white light-emitting electrochemical cells (LECs) have attracted research attention owing to their advantages of simple device structure, low operation voltage and compatibility with solution processes. In this work, we demonstrate a simple approach to obtain white electroluminescence (EL) from non-doped LECs based on a blue-emitting complex. With a relatively thicker emissive layer, red emission can be additionally enhanced by the microcavity effect when the recombination zone moves to appropriate positions. Hence, white EL can be harvested by combining blue emission from the complex and red emission from the microcavity effect. These non-doped white LECs show external quantum efficiencies and power efficiencies up to 5% and 12 lm W-1, respectively. These results show that efficient white EL can be obtained in simple non-doped LECs.
Recent Advances in Solid-State White Light-Emitting Electrochemical Cells
(2014-07-01)
Su, Hai-Ching
;
Cheng, Chia-Yu
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Compared to organic light-emitting diodes, solid-state light-emitting electrochemical cells (LECs) exhibit advantages of simple device structures, low operation voltages, and compatibility with air-stable metal electrodes. Since the first demonstration of white LECs in 1997, the cells have been studied extensively, due to their potential applications in solid-state lighting. This article reviews the development of white LECs based on conjugated polymers and cationic transition metal complexes. Important achievements of each work on white LECs are highlighted. Finally, the outlook for future development of white LECs is discussed.
Recent Advances in Solid-State White Light-Emitting Electrochemical Cells
(2014-07-01)
Su, Hai-Ching
;
Cheng, Chia-Yu
;
照明與能源光電研究所
;
光電工程學系
;
Institute of Lighting and Energy Photonics
Compared to organic light-emitting diodes, solid-state light-emitting electrochemical cells (LECs) exhibit advantages of simple device structures, low operation voltages, and compatibility with air-stable metal electrodes. Since the first demonstration of white LECs in 1997, the cells have been studied extensively, due to their potential applications in solid-state lighting. This article reviews the development of white LECs based on conjugated polymers and cationic transition metal complexes. Important achievements of each work on white LECs are highlighted. Finally, the outlook for future development of white LECs is discussed.