Low-temperature vacuum deposition of green phosphorescent OLED devices using close-space sublimation of spirobifluorene hosts

Abstract

Commercial organic light-emitting diode (OLED) displays are mainly produced by line-of-sight vacuum thermal evaporation (VTE) methods that operate at high temperatures with low material utilization, exerting thermal stress on shadow masks and driving up costs. Further advancement of OLED displays towards higher resolutions at reduced cost demands more efficient deposition sources and OLED materials that can be reliably evaporated at low temperatures. In this study, we utilized close-space sublimation (CSS), an area deposition technique with a high material utilization rate, to lower the evaporation temperature of materials and deposition time drastically. By employing a spirobifluorene-based host that has a matching CSS profile with common iridium-based dopants, we have successfully reduced the evaporation temperature of the emitting layer (EML) to as low as 120 °C in CSS, less than half of the temperature required in VTE, and shortened the deposition time from minutes to seconds. The CSS-deposited green phosphorescent OLEDs exhibited comparable efficiencies with their VTE-deposited counterparts and demonstrated promising lifetimes.