| Abstract
| - Efficient high-energy phosphorescent organic light-emitting diodes require host matrix materials with very high triplet energies. The use of tetraarylsilanes as wide energy gap host materials for blue devices is discussed.
- Four ultrahigh energy gap organosilicon compounds [diphenyldi(o-tolyl)silane (UGH1),p-bis(triphenylsilyl)benzene (UGH2), m-bis(triphenylsilyl)benzene (UGH3), and 9,9‘-spirobisilaanthracene (UGH4)] were employed as host materials in the emissive layer ofelectrophosphorescent organic light-emitting diodes (OLEDs). The high singlet (∼4.5 eV)and triplet (∼3.5 eV) energies associated with these materials effectively suppress both theelectron and energy transfer quenching pathways between the emissive dopant and the hostmaterial, leading to deep blue phosphorescent devices with high (∼10%) external quantumefficiencies. Furthermore, by direct charge injection from the adjacent hole and electrontransport layers onto the phosphor doped into the UGH matrix, exciton formation occursdirectly on the dopant, thereby eliminating exchange energy losses characteristic of guest−host energy transfer. We discuss the material design, and present device data for OLEDsemploying UGHs. Among the four host materials, UGH2 and UGH3 have higher quantumefficiencies than UGH1 when used in OLEDs. Rapid device degradation was observed forthe UGH4-based device due to electro- and/or photooxidation of the diphenylmethane moietyin UGH4. In addition to showing that UGH materials can be used to fabricate efficient blueOLEDs, we demonstrate that very high device efficiencies can be achieved in structureswhere the dopant transports both charge and excitons.
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