Browsing by Author "Hsu, Jia-Hong"

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Host-only solid-state near-infrared light-emitting electrochemical cells based on interferometric spectral tailoring
(2016-02-14)
Hsu, Jia-Hong
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Su, Hai-Ching
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照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Solid-state near-infrared (NIR) light-emitting electrochemical cells (LECs) possess great potential in applications of NIR light sources due to their simple device structure, compatibility with large area and flexible substrates and low operating voltage. However, common host-guest NIR LECs suffer from the problem of significantly enhanced residual host emission upon increasing the bias voltage to achieve a higher NIR light output. A higher NIR light output can only be obtained at the expense of spectral purity in host-guest NIR LECs. To enhance the NIR light output of LECs without sacrificing the spectral purity significantly, a novel approach to generate NIR EL from host-only red-emitting LECs by adjusting the device thickness to modify the microcavity effect is proposed. NIR EL from host-only red-emitting LECs can be realized by adjusting the device thickness to shift the peak wavelength for constructive interference at the NIR spectral region. NIR EL resulting from the microcavity effect is relatively insensitive to bias voltage. Therefore, without losing spectral purity significantly, a 20x enhancement in the NIR output has been obtained in comparison to the previously reported value from host-guest NIR LECs. These results reveal that tailoring the EL spectra of host-only red-emitting LECs via modifying the microcavity effect would be a promising way to generate a higher NIR light output without suffering from the residual host emission problem of host-guest NIR LECs.
Improving the carrier balance of light-emitting electrochemical cells based on ionic transition metal complexes
(2015-01-01)
Su, Hai-Ching
;
Hsu, Jia-Hong
;
照明與能源光電研究所
;
Institute of Lighting and Energy Photonics
Recently, solid-state light-emitting electrochemical cells (LECs) based on ionic transition metal complexes (iTMCs) have attracted much research interest since they have the advantages of a simple device structure, a low operation voltage and compatibility with air-stable electrodes. These properties enable LECs to be cost-effective, versatile and power-efficient organic light-emitting sources. However, it is generally not easy to modify the molecular structure to achieve balanced carrier mobilities without altering the photoluminescence quantum yield of the iTMC. Furthermore, the carrier balance and the consequent device efficiency of single-layered LECs would not be easy to optimize since no carrier injection and transport layers can be used. In this perspective, some reported techniques to improve carrier balance of LECs based on iTMCs are described and reviewed. The importance and impact of these studies are highlighted. The effects on device lifetime and turn-on time because of employing these techniques to improve the carrier balance are also discussed. This perspective concludes that even with electrochemically doped layers, improving the carrier balance of LECs would be required for realizing efficient electroluminescent emission from simple-structure organic light-emitting sources.
Non-doped solid-state white light-emitting electrochemical cells employing the microcavity effect
(2015-03-14)
Lin, Guan-Rung
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Chen, Hsiao-Fan
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Shih, Hsien-Chang
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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.