Contrast improvement of organic light-emitting devices with Sm:Ag cathode

Sm:Ag, easily fabricated via simple thermal evaporation, was investigated as a single-layer light-absorbing cathode to increase the contrast ratio of organic light-emitting devices (OLEDs). The performance of OLEDs with Sm:Ag cathode was found to be comparable to that of the traditional OLEDs with Mg:Ag cathode in terms of brightness, electroluminescence (EL) efficiency, and turn-on voltage. The maximum EL efficiency of the device with Sm:Ag black cathode is 2.72cd∕A at 15V, while the contrast ratio reaches 390:1 at 10V under 140 lx of ambient light, which is 8 times better than that of the traditional device. The lower EL efficiency and enhanced contrast are due to the reduced optical reflectance of Sm:Ag black cathode, which was calculated to be about 0.15.