Carbazole-diphenylimidazole based bipolar material and its application in blue, green and red single layer OLEDs by solution processing

Single layer structure is an ideal way to realize the low cost solution processed organic light-emitting diodes (OLEDs). Efficient electroluminescent material with hole and electron transport characters as well as suitable triplet energy levels is highly desired to realize single layer OLEDs with good performance. In this work, a bipolar compound with carbazole as electron donor and 4,5-diphenylimidazoleas as electron acceptor has been successfully synthesized and applied as emitting layer for both non-doped and doped single layer OLEDs fabricated by solution processing. A pure blue emission achieved in the non-doped single layer OLED with a current efficiency of 0.38 cd A⁻¹, luminance up to 672 cd m⁻². The single layer doped OLEDs with the bipolar compound as host achieved blue, green and red phosphorescence OLEDs with current efficiency of 0.083, 13.42, 2.58 cd A⁻¹ and luminance up to 108, 17103, 1347 cd m⁻², respectively. The performance of single layer OLEDs has been greatly improved by bipolar emitting materials which show a great potential to simplify the configuration of OLEDs.