Browsing by Author "Lin, Chien-Hsiang"

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Cationic Ir-III Emitters with Near-Infrared Emission Beyond 800 nm and Their Use in Light-Emitting Electrochemical Cells
(2019-04-11)
Chen, Guan-Yu
;
Chang, Bo-Ren
;
Shih, Ting-An
;
Lin, Chien-Hsiang
;
Lo, Chieh-Liang
Solid-state near-infrared (NIR) light-emitting devices have recently received considerable attention as MR light sources that can penetrate deep into human tissue and are suitable for bioimaging and labeling. in addition, solidstate NIR light-emitting electrochemical cells (LECs) have shown several promising advantages over NIR organic light-emitting devices (OLEDs). However, among the reported NIR LECs based on ionic transition-metal complexes (iTMCs), there is currently no iridium-based LEC that displays NIR electroluminescence (EL) peaks near to or above 800 nm. In this report we demonstrate a simple method for adjusting the energy gap between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) of iridium-based iTMCs to generate NIR emission. We describe a series of novel ionic iridium complexes with very small energy gaps, namely NIR1-NIR6, in which 2,3-diphenylbenzo[g]quinoxaline moieties mainly take charge of the HOMO energy levels and 2,2'-biquinoline, 2-(quinolin-2-yl)quinazoline, and 2,2'-bibenzo[d]thiazole moieties mainly control the LUMO energy levels. All the complexes exhibited NIR phosphorescence, with emission maxima up to 850 nm, and have been applied as components in LECs, showing a maximum external quantum efficiency (EQE) of 0.05% in the EL devices. By using a host-guest emissive system, with the iridium complex RED as the host and the complex NIR3 or NIR6 as guest, the highest EQE of the LECs can be further enhanced to above 0.1%.
Combinational Approach To Realize Highly Efficient Light-Emitting Electrochemical Cells
(2020-03-25)
Yi, Rong-Huei
;
Lo, Chieh-Liang
;
Luo, Dian
;
Lin, Chien-Hsiang
;
Weng, Shu-Wen
Light-emitting electrochemical cells (LECs) show high technical potential for display and lighting utilizations owing to the superior properties of solution processability, low operation voltage, and employing inert cathodes. For maximizing the device efficiency, three approaches including development of efficient emissive materials, optimizing the carrier balance, and maximizing the light extraction have been reported. However, most reported works focused on only one of the three optimization approaches. In this work, a combinational approach is demonstrated to optimize the device efficiency of LECs. A sophisticatedly designed yellow complex exhibiting a superior steric hindrance and a good carrier balance is proposed as the emissive material of light-emitting electrochemical cells and thus the external quantum efficiency (EQE) is up to 13.6%. With an improved carrier balance and reduced self-quenching by employing the host-guest strategy, the device EQE can be enhanced to 16.9%. Finally, a diffusive layer embedded between the glass substrate and the indium-tin-oxide layer is utilized to scatter the light trapped in the layered device structure, and consequently, a high EQE of 23.7% can be obtained. Such an EQE is impressive and consequently proves that the proposed combinational approach including adopting efficient emissive materials, optimizing the carrier balance, and maximizing the light extraction is effective in realizing highly efficient LECs.
Efficient and Saturated Red Light-Emitting Electrochemical Cells Based on Cationic Iridium(III) Complexes with EQE up to 9.4 %
(1970-01-01)
Yu, Guang-Xiang
;
Lin, Chien-Hsiang
;
Liu, You-Xuan
;
Yi, Rong-Huei
;
Chen, Guan-Yu
Solid-state light-emitting electrochemical cells (LECs) have several advantages, such as low-voltage operation, compatibility with inert metal electrodes, large-area flexible substrates, and simple solution-processable device architectures. However, most of the studies on saturated red LECs show low or moderate device efficiencies (external quantum efficiency (EQE) <3.3 %). In this work, we demonstrate a series of five red-emitting cationic iridium complexes (RED1--RED5) with 2,2 '-biquinoline ligands and test their electroluminescence (EL) characteristics in LECs. The Commission Internationale de l ' Eclairage (CIE) 1931 coordinates for the LECs based on these complexes are all beyond the National Television System Committee (NTSC) red standard point (0.67, 0.33). The maximal EQE of the neat-film RED1-based LECs reaches 7.4 %. The reddest complex, RED3, is doped in the blue-emitting host complex, BG, to fabricate host-guest LECs. The maximal EQE of the host-guest LECs (1 wt % complex RED3) reaches 9.4 %, which is among the highest reported for the saturated red LECs.