Efficiency enhancement of solution‐processed single‐layer blue‐phosphorescence organic light‐emitting devices having co‐host materials of polymer (PVK) and small‐molecule (SimCP2)

Abstract

Abstract— A new type of single‐layer blue‐phosphorescence organic light‐emitting devices (OLEDs) containing poly(9‐vinylcarbazole) (PVK) and small‐molecule‐based amorphous ambipolar bis(3,5‐di(9H‐carbazol‐9‐yl)phenyl) diphenylsilane (SimCP2) as the co‐host material have been demonstrated. All active materials [PVK, SimCP2, Flrpic (blue‐phosphorescence dopant), and OXD‐7 (electron transport)] were mixed in a single layer for solution processing in the fabrication of OLEDs. The SimCP2 small‐molecule host has adequate high electron and hole‐carrier mobiltieis of ∼10−4 cm2/V‐sec and a sufficiently large triplet state energy of ∼2.70 eV in confining emission energy on FIrpic. Based on such an architecture for single‐layer devices, a maximum external quantum efficiency of 6.2%, luminous efficiency of 15.8 cd/A, luminous power efficiency of 11 lm/W, and Commision Internale de l'Eclairage (CIEx,y) coordinates of (0.14,0.32) were achieved. Compared with those having PVK as the single‐host material, the improvement in the device performance is attributed to the balance of hole and electron mobilities of the co‐host material, efficient triplet‐state energy confinement on FIrpic, and the high homogeneity of the thin‐film active layer. Flexible blue‐phosphorescence OLEDs based on solution‐processed SimCP2 host material (withou PVK) have been demonstrated as well.