Inverted topside-emitting organic light-emitting diodes for active-matrix OLED displays

摘要

Top-emitting organic light-emitting diodes (OLEDS) for next-generation active-matrix OLED-displays (AM-OLEDs) are discussed. The emission of light via the conductive transparent top-contact is considered necessary in terms of integrating OLED-technology to standard Si-based driver circuitry. The inverted OLED configuration (IOLED) in particular allows for the incorporation of more powerful n-channel field-effect transistors preferentially used for driver backplanes in AM-OLED displays. The use of the highly conductive polymer PEDOT:PSS as hole injection layer yields anodes with an extremely low contact resistance. The non-destructive spin-coating is enabled by a hydrophobic buffer layer such as pentacene. The overlying transparent electrode was realized employing low-power radio-frequency magnetron sputter-deposition of indium-tin-oxide (ITO). Additionally, a cathode with an interfacially metal-doped electron-injecting layer is proposed. Hybrid inverted OLEDs utilizing the fluorescent emitter system Alq_3:Ph-QAD allowed efficiencies of 2.7 lm/W around 150 cd/m~2. Device efficiencies are increased by employing a phosphorescent dye Ir(ppy)_3 doped into the hole-transporter TCTA. Such phosphorescent hybrid IOLEDs exhibit peak efficiencies of 19.6 cd/A and 5.8 lm/W at 127 cd/m~2. Thus, the main requirements for a use of hybrid inverted lOLEDs in AM-OLED-displays are satisfied.