Imidazolyl‐Phenylcarbazole‐Based Host Materials and Their Use for Co‐host Designs in Phosphorescent OLEDs

Abstract

In recent years, owing to the demand for highefficiency phosphorescent organic light-emitting devices (PhOLEDs), many studies have been conducted on the development of bipolar host materials. A series of imidazolylphenylcarbazole-based host materials, i. e., im-CzP, im-CzPCz, im-CzPtBu, and im-OCzP, were synthesized to obtain highefficiency green and red-emitting PhOLEDs. With im-OCzP as the host, satisfactory peak efficiencies of 22.2 (77.0 cd A À 1 and 93.1 lm W À 1 ) and 14.1 % (9.0 cd A À 1 and 10.1 lm W À 1 ) could be obtained, respectively. To further improve the performance of the devices, an electron transport material, bis-4,6-(3,5-di-3pyridylphenyl)-2-methylpyrimidine (B3PyMPM) was selected to construct a co-hosted system. The efficiency of im-OCzP combined with B3PyMPM forming co-hosts could also achieve high values of 23.0 (80.0 cd A À 1 and 98.8 lm W À 1 ) and 16.5 % (10.2 cd A À 1 and 13.4 lm W À 1 ) for green and red PhOLEDs, respectively. These results exhibited that the proposed bipolar hosts have great flexibility in adjusting the carrier balance of EML in OLEDs, demonstrating their ingenious design and high potential.

True- to Sky-Blue Emitters Bearing the Thiazolo[5,4-d]thiazole Electron Acceptor for Single and Tandem Organic Light-Emitting Diodes

“…In addition, the energy was effectively transferred from the host to the guest in both the blue-emitting and green-emitting devices, and the exciton was well confined within the EML. 57 From the current density−voltage (J−V) curves shown in Figure 7b, device C showed a much lower turn-on voltage of 2.6 V compared to those of devices A and B, due to the simpler device architecture as well as the smaller energy band gaps of the host−guest system. Nevertheless, devices A and B present a higher current density at high voltage ranges, indicating better carrier transport capability or a lower possibility of carrier trapping.…”

“…As shown in Figure a, the EL spectra of devices A, B, and C were similar to the respective PL spectra of the emitters measured in toluene, showing that the exciton formed on the dopant only. In addition, the energy was effectively transferred from the host to the guest in both the blue-emitting and green-emitting devices, and the exciton was well confined within the EML . From the current density–voltage ( J – V ) curves shown in Figure b, device C showed a much lower turn-on voltage of 2.6 V compared to those of devices A and B, due to the simpler device architecture as well as the smaller energy band gaps of the host–guest system.…”

Highly efficient (EQE > 27%) Yellow OLEDs using spiro[fluorene-9,9′-phenanthren-10′-one]-carbazole-based donor–acceptor–donor host materials

“…28–30 Two commonly used hole-transporting materials, namely, bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4′′-tris( N -carbazolyl)triphenylamine (TCTA), were chosen to form step-wise hole-transport layers (HTLs), aiming to promote smooth hole injection from the HTL into the EML. 31 Moreover, as mentioned above, CN-T2T with appropriate electron transport properties was used as the electron transport layer (ETL). The three device architectures were nearly identical, except for the EML structures.…”

Improved Efficiency and Stability of Red Phosphorescent Organic Light-Emitting Diodes via Selective Deuteration

“…The property comparison of the device with and without the DMIC-CZ buffer layer is shown in Figure S7. The former one achieves better EQE and higher current density under the same driving voltage, indicating that the charge balance has been improved . It can be inferred that the DMIC-CZ layer prevents the triplet excitons from diffusing into TAPC layer, thus confining the energy transfer in the EML …”

“…The former one achieves better EQE and higher current density under the same driving voltage, indicating that the charge balance has been improved. 32 It can be inferred that the DMIC-CZ layer prevents the triplet excitons from diffusing into TAPC layer, thus confining the energy transfer in the EML. 33 Scheme Finally, four groups of devices (G1H/D and G2H/D) utilizing the complexes of Ir(mpiq) 2 divm, Ir(mpiq) 2 divm-d 1 , Ir(mpiq) 2 dmbm, and Ir(mpiq) 2 dmbm-d 1 , respectively, in a number of 40 counts each, were parallelly fabricated with the same device architecture.…”