No abstract

Two bipolar molecules CzT2.1 and CzT2.2 are examined as electron acceptors to form exciplexes with electron donors 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4′′-tris(carbazol-9-yl)-triphenylamine (TCTA), respectively.

Organic light-emitting diodes (OLEDs) used as phototherapy light sources require sufficient spectral distribution in the effective wavelength ranges and low operating voltages. Herein, a double emitting layer structure consisting of a red-emitting Ir(piq)2acac and a deep-red Ir(fliq)2acac was designed to generate a broad electroluminescence spectrum. An efficient TCTA:CN-T2T exciplex system was used as the host of the emitting layer, facilitating effective energy transfer from the exciplex host to the red and deep-red phosphors. The materials used in the exciplex host were also used as the carrier transport layers to eliminate the energy barriers and thus increase the current density. The hole injection layer structures were varied to examine the hole injection capabilities and the carrier balance. The resulting optimized phosphorescent OLEDs with a broad spectral profile exhibit a 90% coverage ratio in the target ranges from 630 to 690 nm, together with a high peak efficiency of 19.1% (10.2 cd/A and 13.8 lm/W). The proposed device only needs 5.2 V to achieve a power density of 5 mW/cm2, implying that the device could be driven via two series-connected button cell batteries. These results illustrate the feasibility of our design concepts and demonstrate the realization of a portable and lightweight OLED phototherapy light source.

A series of emitters displaying efficient photoluminescence (PL) and electroluminescence (EL) into the trueto sky-blue regions is herein described and employed as electroluminescent materials for the fabrication of efficient blue organic light-emitting diodes (OLEDs). The compounds possess linear, yet a twisted, donor−π−acceptor−π−donor (D−π−A−π− D) architecture, where D and A are a (substituted) carbazole (Cz) and thiazolo [5,4-d]thiazole (TzTz) moiety as the electron donor and accepting unit, respectively. D = 9H-carbazol-9-yl and 3,6-ditert-butyl-9H-carbazol-9-yl for compounds TzTz-PCz2 and TzTz-PtbCz2, respectively. In dilute CH 2 Cl 2 solutions, both compounds display intense (PL quantum yield = 60−74%) and short-lived (τ = ca. 0.8−2.0 ns) luminescence arising from an intramolecular charge-transfer ( 1 ICT) excited state and falling into the sky-blue to the greenish-blue region (λ em = 448−502 nm). Compared to the previously reported TzTz-TPA parental emitters that features two triphenylamine (TPA) donor groups, the highly twisted nature and less extended π-conjugation of the donor−acceptor TzTz-PCz2 and TzTz-PtbCz2 counterparts herein presented enable to widen the HOMO−LUMO energy gaps and warrant blue shifting of the emission. Finally, OLED devices fabricated by employing the herein proposed emitters are presented as well with both single-and tandem-device architectures. The so-prepared OLEDs display true-blue to sky-blue EL peaking at λ EL,max = 460 nm (TzTz-PCz2) and 467−470 nm (TzTz-PtbCz2) and achieve maximum external quantum efficiency and luminance of 10.2% and 44,851 cd m −2 (for TzTz-PtbCz2) in the case of a tandem device, respectively, with a mitigated roll-off efficiency. These results demonstrate that the tandem device employing these TzTz donor−acceptor blue emitters raises the feasibility of fluorescent compounds to compete with other potential emitters in practical applications.

We propose a new flexible transparent composite electrode that uses an ultra-thin silver-chromium (AgCr) alloy film to increase the conductivity of a Mo-doped GaZnO (MGZO) thin film and to maintain...