Solution-Processable Hosts Constructed by Carbazole/PO Substituted Tetraphenylsilanes for Efficient Blue Electrophosphorescent Devices

Two new solution-processable wide bandgap materials, bis(4-((4-(9-H-carbazol-9-yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (CS2PO) and bis(4-((4-(9-H-(3,9-bicarbazol)-9-yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (DCS2PO), have been developed for blue phosphorescent light-emitting diodes by coupling an electron-donating carbazole moiety and an electron-accepting PO unit together via double-silicon bridges. Both of them have been characterized as having high glass transition temperatures of 159-199 degrees C, good solubility in common organic solvent (20 mg mL(-1)), wide optical gap (3.37-3.55 eV) and high triplet energy levels (2.97-3.04 eV). As compared with their corresponding single-silicon bridged compounds, this design strategy of extending molecular structure endows CS2PO and DCS2PO with higher thermal stability, better solution processability and more stable film morphology without lowering their triplet energies. As a result, DCS2PO/FIrpic doped blue phosphorescent device fabricated by spin-coating method shows the best electroluminescent performance with a maximum current efficiency of 26.5 cd A(-1), a maximum power efficiency of 8.66 lm W-1, and a maximum external quantum efficiency of 13.6%, which is one of the highest efficiencies among small molecular devices with the same deposition process and device configuration.