Effect of Al：Ag alloy cathode on the performance of transparent organic light-emitting devices

Transparent organic light-emitting devices（TOLEDs） based on a stacked alloy cathode of LiF/Al：Ag are investigated. The devices have a structure of indium-tin-oxide（ITO）/4,4′,4′′-Tris[2-naphthyl（phenyl）amino]triphenylamine（2T-NATA）（25 nm）/N,N＇-Di-[（1-naphthyl）-N,N＇-diphenyl]-1,1＇-biphenyl-4,4＇-diamine（NPB）（40 nm）/tris-（8-hydroxyquinoline） aluminum（Al（q3））（50 nm）/LiF（1 nm）/Al：Ag（1：3）（x）, where the thicknesses of cathode metal layers（Al：Ag） are adjusted, respectively, from 70 nm to 100 nm. In the experiment, it is found that the Li F（1 nm）/Al：Ag（1：3）（75 nm） has good electron injection efficiency. Compared with an Al-only cathode, the turn-on voltage is lowered. At the voltage of 10 V, the luminances for bottom emission from ITO anode side and top emission from metal cathode side are 2 459 cd/m~2 and 1 729 cd/m~2, respectively. Thanks to electron injection enhancement by using Al：Ag cathode, we can obtain a better energy level matching between the cathode and the organic layer, thus the devices have lower turn-on voltage and higher luminance. The total transmittance of the devices can achieve about 40% at the wavelength of 550 nm.