Improved Device Lifetime In Organic Light Emitting Devices By Using a Solution-Processed Mixing Single Layer Structure

Device stability in an organic light emitting devices (OLEDs) with a solution-processed mixing single layer by mixing of hole transport material (α-NPD), host materials tris-(8-hydroxy-quinoline) aluminum (Alq3), electron transport material 2,5-bis(6′-(2′,2″-bipyridyl))-1,1- dimethyl-3,4-diphenylsilole (PyPySPyPy) and dope material 5,6,11,12-tetraphenylnaphthacene (rubrene) was investigated. Maximum power efficiency of 5.6 lm/W was obtained by optimizing the mixing ratio of α-NPD: Alq3: rubrene:PyPySPyPy = 30:50:1:20. Luminance and power efficiency of mixed single layer device was largely improved compared to tri-layer heterojunction device. Lifetime testing demonstrated that the mixed single layer device exhibited longer operational lifetime of 340 hours, which was three times longer than the 105 hours for tri-layer device. Origin of improved device stability is analyzed by evaluating the current-voltage characteristics, dark sports growth and the polarized optical microscope images of mixed organic films.