Browsing by Author "Chen, Chao-Tsen"

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Achieving high-efficiency non-doped blue organic light-emitting diodes: charge-balance control of bipolar blue fluorescent materials with reduced hole-mobility
(2009)
Chi, Chih-Chin
;
Chiang, Chih-Long
;
Liu, Shun-Wei
;
Yueh, Han
;
Chen, Chin-Ti
We found an unusual way in improving electroluminescence efficiency of blue organic light-emitting diodes (OLEDs). Two electron deficient 4,5-diazafluorene- or di(2,2'-pyridyl)-containing blue fluorophores, PhSP(N2)DPV (4,5-diaza-2'-diphenylamino-7'-(2,2"-diphenylvinyl)-9,9'-spirobifluorene) and PhF(py2)DPV (N-[7-(2,2- diphenylvinyl)- 9,9'-di(2,2"-pyridyl)-2-fluorenyl]-N,N-diphenylamine), were synthesized and characterized for non-doped blue OLEDs. Whereas PhF(py2)DPV OLED performs ordinarily, PhSP(N2)DPV OLED outperforms previously known PhSPDPV (2-diphenylamino-7-diphenylvinyl-9,9'-spirobifluorene) OLED significantly: maximum external quantum efficiency of similar to 5% (4.6% at 20 mA cm(-2)) and the peak electroluminance of 60510 cd m(-2) (1810 cd m(-2) at 20 mA cm(-2)) versus 3.4% (2.9% at 20 mA cm(-2)) and 33020 cd m(-2) (910 cd m(-2) at 20 mA cm(-2)) of PhSPDPV OLED. We attribute the superior performance of PhSP(N2)DPV OLED to the good charge balancing, which is in turn due to the very low hole mobility of PhSP(N2)DPV. The experimental results reveal that the electron-deficient moiety, 4,5-diazafluorene or di(2,2'-dipyridyl), increases electron affinity but reduces the hole mobility. Electron mobility, determined by time-of-flight (TOF) method, is 5 x 10(-5) and 5 x 10(-4) cm(2) V(-1) s(-1) (at an electric field of 4.9 x 10(5) V cm(-1)) for PhSP(N2)DPV and PhF(py2)DPV, respectively. Surprisingly, they are not higher than 8 x 10(-4) cm(2) V(-1) s(-1) of nonpolar PhSPDPV. On the other hand, hole mobility is 2 x 10(-6) and 2 x 10(-4) cm(2) V(-1) s(-1) for PhSP(N2)DPV and PhF(py2)DPV, respectively, and they are both significantly lower than 6 x 10(-3) cm(2) V(-1) s(-1) of PhSPDPV. For PhSP(N2)DPV and PhF(py2)DPV bipolar blue fluorophores, we have demonstrated that electron-transporting and light-emitting functions involve different molecular halves. The design of such molecular halves greatly facilitates the optical and electronic optimizations of fluorophores for high-performance OLEDs.
High performance hybrid white OLEDs based on new platinum complexes and new blue fluorescence host
(2014-01-01)
Poloek, Anurach
;
Wang, Chieh
;
Lin, Chiao-Wen
;
Chen, Chin-Ti
;
Chen, Chao-Tsen
A new series of platinum complexes containing 4-hydroxy-1,5-naphtyridine derivative with different substitutens such as methyl, dimethyl, phenyl, phenoxy, dimethyl amine, piperidine, morpholine, phenoxazine or carbazole unit as the primary ligand and 2-(2,4-difluorophenyl)pyridine as the secondary ligand were synthesized and characterized. Single crystal X-ray diffraction studies of FPtOPhND, FPtCzND and FPtdmaND showed trans-coordinated in distorted square-planar geometry. Their photophysical properties and electrochemical properties were examined. All platinum complexes in these series exhibited dual emissions not only in solution but also in solid state thin film. Employing CBP or 4P-NPD as host material, high efficiency monochromatic and high quality hybrid white organic light emitting diodes (WOLEDs) were achieved with the single platinum complex dopant device, a relatively simple device configuration.
New platinum complexes exhibiting host dependent photoluminescence as single dopants in double emitting layer, voltage independent hybrid white electroluminescence devices
(2015-01-01)
Poloek, Anurach
;
Wang, Chieh
;
Chang, Yung-Ting
;
Lin, Chiao-Wen
;
Chen, Chao-Tsen
Four heteroleptic platinum complexes (FPtXNDs) bearing 4-hydroxy-1,5-naphthyridine (XND) derivatives functionalized with phenyl (X = Ph), dimethylamino (X = dma), morpholino (X = mor), or phenoxazino (X = pxz) units as one ligand and 2-(2,4-difluorophenyl) pyridine (F) as the other common ligand were newly synthesized and characterized. Each platinum complex has absorption and photoluminescence (PL) spectroscopic characteristics. As demonstrated by X-ray crystallography (of FPtdmaND and FPtpxzND), electrochemical and theoretical studies, the unusual spectroscopic features of FPtpxzND (such as its weak absorption band around 450-600 nm, its significant concentration dependent solution PL wavelength but low host dependent thin film PL wavelength (which is relatively long) and its particularly low solution PL quantum yield (Phi(PL))) the relatively strong absorption of FPtdmaND and FPtmorND, and the relatively long PL wavelength of FPtPhND have been reasonably explained. After each platinum complex had been examined for monochromatic organic lightemitting diodes (OLEDs), having a relatively high FPL as well as an appropriate greenish yellow PL in the monomeric form and an orange to red PL in the aggregate/excimeric form, FPtdmaND and FPtmorND have been chosen as dopant materials in the construction of single or double emitting layer (EML) hybrid white organic light-emitting diodes (OLEDs). A high performance warm white electroluminescence (EL) (CIEx,y (0.42-0.43, 0.43-0.44)) was obtained where the same platinum complex dopant FPtdmaND was doped (5 or 8 wt%) in two EMLs, 4,4\'-di(9H-carbazol-9-yl)-1,1\'-biphenyl (CBP) harvesting monomeric emission and the highly fluorescent blue N,N\'-di-1-naphthalenyl-N,N\'-diphenyl-[1,1\':4\',1 \'\':4 \'\',1\'\'\'-quaterphenyl]-4,4\'\'\'-diamine (4P-NPD) harvesting excimer/aggregate emission. This warm white EL showed a high colour rendering index (CRI) of 86-88, and a reasonably good EL efficiency of 9.7%, 22.5 cd A(-1), or 10.7 lm W-1. EL with improved white chromaticity (CIEx,y (0.37-0.39, 0.39-0.41)) can be obtained using FPtmorND as the single dopant, although it has a somewhat inferior CRI (84-86) and EL efficiency (8.3%, 20.1 cd A(-1), or 9.5 lm W-1). Nevertheless, both double EML hybrid white OLEDs exhibit a rather constant CRI and CIEx,y under a driving voltage between 7 and 10 V.
Oligothiophenes and alkyl side-chain arrangement the structure-property study of their diketopyrrolopyrrole copolymers for organic photovoltaics
(2018-10-01)
Wu, Jhao-Lin
;
Lin, Chiao-Wen
;
Golder, Jan
;
Lin, Tsu-Wei
;
Chen, Chin-Ti
We have synthesized and characterized a series of diketopyrrolopyrrole (DPP)-oligothiophene copolymers, of which the number of regioregular oligothiophene ring (2T, 3T and 4T) and the arrangement of the alkyl side-chain on regioirregular quarterthiophene (4T0, 4T1 and 4T2) are variable. The side chains with regioregular lead to more planar copolymer backbones and higher short circuit current (J(sc)), but backbone torsion (due to regioirregular side chains) generates greater open-circuit voltages (V-OC) for DPP-oligothiophene copolymers. The increasing thiophene ring progressively raises HOMO energy level of copolymers but marginally affects their band gaps. Additionally, the HOMO energy level was found declined significantly with side-chain regioirregularity, because of reducing length of pi-conjugation. The HDDPP4T0 exhibits the strongest absorption, extensive network structure, and high hole mobility (mu(h )= 6.04 x 10(-4)cm(2)V(-1) s(-1)). These characteristics contribute to the exceptional high J(SC) of 18.96 mA/cm(2) for OPV with PCE = 6.12%. However, the HDDPP4T1 having an optimal combination of pi-conjugation and energy level affords the second highest V-OC (0.73 V) and the third highest J(SC) (16.89 mA/cm(2)), resulting the best PCE of 7.51% among all. X-ray scattering, transmission electron microscopy, atomic force microscopy, and space-charge-limited-current (SCLC) measurements reveal that the solvent additive of diphenylether (DPE) enables PC71BM-blended copolymers thin film in crystallinic fibril with enhanced hole mobility.
Polymer side-chain substituents elucidate thermochromism of benzodithiophene-dithiophenylacrylonitrile copolymers - polymer solubility correlation of thermochromism and photovoltaic performance
(2017-06-28)
Chen, Hung-Yang
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Lin, Chiao-Wen
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Chen, Chin-Ti
;
Chen, Chao-Tsen
;
Golder, Jan
Nine pBCNx polymers based on a donor-p-acceptor benzo[1,2-b:4,5-b']dithiophene-(E)-2,3-di(thiophen-2-yl) acrylonitrile main-chain structure and n-octyl/2-ethylhexyl as the side-chain substituents have been designed and synthesized. The thermochromism of the pBCNx polymers has been carefully examined in both solution and the thin-film state. With additional evidences from Raman spectroscopy and AFM microscopy, we have deciphered the varied colours of nine pBCNx polymers in solution and the pronounced thin-film thermochromism only observed for certain pBCNx polymers, i.e., pBCN4, pBCN5, pBCN6, and pBCN8. The alkyl side-chain, and hence the solubility or aggregation of pBCNx polymers, is a main factor of the varied colour in solution and the varied thermochromism in the thin film. We have identified that a stronger main-chain and main-chain interaction are present on the (E)-2,3-di(thiophen-2-yl) acrylonitrile moiety, whereas the poor to moderate solubility pBCN3, pBCN5', and pBCN7 exhibit pronounced thermochromism in solution, and pBCN4, pBCN5, pBCN6, and pBCN8 are four polymers which have good solubility in solution and show thermochromism in the thin-film state. We took navy blue pBCN3 (poor solubility), magenta pBCN4 (good solubility), and reddish purple pBCN5' (moderate solubility) for the fabrication of bulk heterojunction organic photovoltaics (OPVs). With a solvent annealing treatment, the power conversion efficiency of the OPVs has been improved significantly from 4.7% to 6.2% for the good solubility pBCN4, but there is little and no improvement for the moderate solubility pBCN5' and poor solubility pBCN3, respectively. Our study verifies that the good OPV performance of the pBCNx polymers can be correlated to the pronounced thin-film thermochromism. A good solubility of the polymer is a common characteristic of a material with significant thin-film thermochromism and good OPV performance.
SimCP3-An Advanced Homologue of SimCP2 as a Solution-Processed Small Molecular Host Material for Blue Phosphorescence Organic Light-Emitting Diodes
(2016-10-01)
Lee, Yi-Ting
;
Chang, Yung-Ting
;
Wu, Cheng-Lung
;
Golder, Jan
;
Chen, Chin-Ti
We have overcome the synthetic difficulty of 9,9',9 '',9 ''',9 '''',9 '''''-((phenylsilanetriyl) tris(benzene-5,3,1-triyl))hexakis(9H-carbazole) (SimCP3) an advanced homologue of previously known SimCP2 as a solution-processed, high triplet gap energy host material for a blue phosphorescence dopant. A series of organic light-emitting diodes based on blue phosphorescence dopant iridium (III) bis(4,6-difluorophenylpyridinato) picolate, FIrpic, were fabricated and tested to demonstrate the validity of solution-processed SimCP3 in the device fabrication.
Solid state molecular packing and photoluminescence of platinum complexes based on 1,5-naphthyridin-4-plate ligands
(2015-01-01)
Chen, Chin-Ti
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Poloek, Anurack
;
Wang, Chieh
;
Lin, Chiao-Wen
;
Chen, Chao-Tsen