Transparent organic light-emitting devices using a MoO₃/Ag/MoO₃ cathode

MoO₃/Ag/MoO₃ (MAM) stacks are investigated for utilization as transparent cathodes in organic light-emitting devices (OLEDs). The stacks can be fabricated using simple thermal evaporation at relatively low temperatures, and can be readily and safely utilized as top electrodes, without causing deposition damage to the organic layers. Results show that it is possible to achieve efficient electron injection from the MAM electrode into organic layers by means of incorporating a suitable electron injection layer (EIL) at the interface. Results also show that a MAM stack can exhibit high optical transmittance, amounting to about 65–80% in the 400–700 nm, and a low sheet resistance (9 Ω/□). A transparent OLED with a MAM cathode incorporated with a 10 nm Bphen: Cs₂CO₃ (10%) EIL is studied. By fine tuning the MAM structure, optimal OLED performance has been achieved: a total luminance of 1300 cd/m² (representing ∼1000 cd/m² and ∼300 cd/m² from the bottom and the top, respectively) at 20 mA/cm² and a corresponding driving voltage of 7.2 V. The OLED exhibits a peak transmittance of ∼90% in the 450–475 nm range, and a transmittance above 45% over the entire visible (i.e., 400–700 nm) range.