Fu-Chuan Fang

Efficient solid-state host-guest light-emitting electrochemical cells based on cationic transition metal complexes

The authors demonstrate highly efficient solid-state light-emitting electrochemical cells (LECs) consisting of green-emitting [Ir(dFppy)2(SB)]+(PF6−) as the host and orange-emitting [Ir(ppy)2(SB)]+(PF6−) as the guest [where dFppy is 2-(2,4-difluorophenyl)pyridine, SB is 4,5-diaza-9,9′-spirobifluorene, and ppy is 2-phenylpyridine]. Photophysical studies show that with the optimized host-guest compositions, the emission is mainly from the guest and photoluminescence quantum yields are largely enhanced over those of pure host and guest films due to suppressed intermolecular interactions. Correspondingly, LECs based on such host-guest cationic complex systems show substantially enhanced quantum efficiencies (power efficiencies) of up to 10.4% (36.8lm∕W), representing a 1.5 times enhancement compared to those of pure host and guest devices. Such results indicate that the host-guest system is essential and useful for achieving highly efficient solid-state LECs.

Triphenylsilyl- and Trityl-Substituted Carbazole-Based Host Materials for Blue Electrophosphorescence

Carbazole-based materials adopting the nonconjugated substitution of triphenylsilyl (-SiPh(3)) and trityl (-CPh(3)) side groups are studied as high-triplet-energy, morphologically, and electrochemically stable host materials with tunable carrier-transport properties for organic blue electrophosphorescence. The developed host materials 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole (CzC), and 9-(4-tert-butylphenyl)-3-(triphenylsilyl)-6-trityl-9H-carbazole (CzCSi) all show high triplet energies of 2.97-3.02 eV, along with high glass transition temperatures of 131-163 degrees C and superior electrochemical stability. Nevertheless, the carrier-transport properties show rather significant dependence on different substitutions. Although three different host materials give similar peak electroluminescence efficiencies at low driving currents, the CzSi host, which has more suitable carrier-transport properties, renders broadened distributions of the triplet excitons in phosphorescent devices, reducing the quenching associated with triplet-triplet annihilation and giving larger resistance against efficiency roll-off at higher brightnesses.

Solid-state light-emitting electrochemical cells employing phosphor-sensitized fluorescence

We report highly efficient phosphor-sensitized solid-state light-emitting electrochemical cells (LECs) utilizing a phosphorescent cationic iridium complex [Ir(dFppy)2(SB)]+(PF6−) as the host and a fluorescent cationic dye (R6G) as the guest. Photophysical studies show that R6G retains a high photoluminescence quantum yield (PLQY) in highly polar media, revealing its suitable use as an emitting guest in an ionic host matrix. Such solid-state LECs achieve quantum efficiency (cd A−1) efficiency, and power efficiency up to 5.5% photon/electron, 19 cd A−1 and 21.3 lm W−1, respectively. The device quantum efficiency achieved is among the highest reported for fluorescent LECs and is higher than one would expect from the PLQY of the R6G fluorescent dye in the host film, thus indicating that phosphor-sensitization is useful for achieving highly efficient fluorescent LECs. Moreover, using narrow-band fluorescent emitters, such as R6G (FWHM, ∼50 nm), is effective in improving the color saturation of solid-state LECs based on cationic complexes.

Versatile one-step introduction of multiple hydrogen-bonding sites onto extended π-conjugated systems

Unprotected arylbiuret units were smoothly introduced onto pi-conjugated structures to afford new supramolecular materials leading to interpenetrated networks.

Photoinduced charge separation in donor–acceptor spiro compounds at metal and metal oxide surfaces: application in dye-sensitized solar cell

Modulated charge separation has been investigated by surface photovoltage spectroscopy in the fixed capacitor arrangement for four different fluorene compounds adsorbed from highly diluted solutions at ultra-thin nanoporous TiO2 (np-TiO2), Au and ITO surfaces. Donor (–N(C6H5)2) and acceptor moieties (–CN, –COOH) were linked by fluorene or spirobisfluorene cores and the chain length has been changed by introducing thiophene. Modulated charge separation by electron injection and intramolecular transport has been separated and directed adsorption of spiro compounds at Au surfaces has been demonstrated. Striking differences between the interaction of linking –CN and –COOH groups and the different substrates were observed. The capability as TiO2 spectral sensitizer of spirobisfluorene donor–acceptor molecules with extended conjugation has been demonstrated. Solar cells exhibit 5.6% energy conversion efficiency, confirming that spiro-configured geometry is a promising route to the design of metal free dyes.

P-151: Efficient Solution-Processable Solid-State Light-Emitting Electrochemical Cells Based on Host-Guest Cationic Phosphorescent Complexes

Efficient solution-processable, small-molecule and single-layered organic light-emitting devices based on host-guest phosphorescent cationic metal complexes are reported. They show high quantum efficiencies (power efficiencies) of up to 10.4% (36.8 lm/W), representing a promising technique for solution-processable OLEDs.

Highly efficient blue phosphorescent OLEDs using large bandgap host materials

The synthesis and properties of 3,6-bis(triphenylsilyl)carbazole as an effective host material for blue electrophosphorescence are reported. The electrochemically active C3 and C6 sites of carbazole are non-conjugated blocked with the steric, bulky and large-gap triphenylsilyls, the resulting new compound retains the large triplet energy of carbazole yet exhibits much enhanced morphological stability and electrochemical stability in comparison with previous carbazole-based host materials. Using this new host material, blue phosphorescent OLEDs having high efficiencies up to 16%, 30.6 cd/A and 26.7 lm/W are demonstrated.