Ca/Ag bilayer cathode for transparent white organic light-emitting devices

We have demonstrated that the compositional modification of the Ca/Ag films is principally responsible for a high transmittance (over 70% in the visible range) and low sheet resistance (10-12 Ω/sq). X-ray photoelectron spectroscopy (XPS) sputter depth profiling of Ca/Ag structure reveals the presence of Ca(OH)2 and Ca metal. A chemical model of the Ca/Ag cathode is proposed. Using transparent ITO anode and Ca (10 nm)/Ag (10 nm) cathode, efficient white organic light-emitting devices (WOLEDs) emitting from both sides have been fabricated. Brightness of 3813 cd/m2 and Commission Internationale de l'Eclairage (CIE) coordinates (0.36, 0.34) at 10 V through ITO anode and values of 1216 cd/m2 and (0.33, 0.30) through Ca/Ag cathode are reported. A low turn-on voltage of 5.5 V is measured.