Browsing by Author "Sun, Ray"

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Effects of incorporating salts with various alkyl chain lengths on carrier balance of light-emitting electrochemical cells
(2014-11-01)
Sun, Ray
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Liao, Chih-Teng
;
Su, Hai-Ching
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照明與能源光電研究所
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Institute of Lighting and Energy Photonics
Recently, solid-state light-emitting electrochemical cells (LECs) have attracted much attention since they have advantages such as low operation voltages, simple device structure and balanced carrier injection. Salts are commonly added in the emissive layer of LECs to provide additional mobile ions and thus to accelerate device response. However, in addition to modified ionic property, carrier balance of LECs would also be tailored by salt additives. In this work, we improve device efficiency of LECs by incorporating imidazole-based salts bearing various alkyl chain lengths. As the alkyl chain length of the added salt increases, the device current decreases and the recombination zone approaches the anode. These results reveal that hole transport in the emissive layer of LEC containing a salt with a larger size would be impeded more significantly than electron transport. When doped with a salt possessing a proper size, nearly doubled device efficiency as compared to that of the neat-film device can be obtained due to improved carrier balance. This work demonstrates a feasible strategy to improve device performance of LECs and clarifies the physical insights of the effect of salt size on carrier balance of LECs. (C) 2014 Elsevier B.V. All rights reserved.
Efficient solid-state white light-emitting electrochemical cells employing embedded red color conversion layers
(2015-01-01)
Lu, Jung-Sheng
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Chen, Hsiao-Fan
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Kuo, Jung-Chin
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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.