Enhanced current efficiency in organic light-emitting devices using 4,4′-N,N′-dicarbazole-biphenyl as hole-buffer layer

Organic light-emitting devices with a hole-buffer layer (HBL) 4,4′-N,N′-dicarbazole-biphenyl (CBP) inserted between ITO anode and hole transporting layer were fabricated. The present of the CBP can balance the hole and electron injections and reduce the hole-leakage to the cathode resulting in the enhancement of the current efficiency. The highest current efficiency of the device with optimum CBP thickness of 4 nm was 5.66 cd/A at 8 V that is nearly 1.5 times than that of the device without the HBL.