Organic Light-Emitting Diodes with Heterojunction of Thiophene/Phenylene Co-Oligomer Derivatives.

Organic light-emitting diodes are fabricated by heterojunction of thiophene/phenylene co-oligomer films using biphenyl-capped bithiophene (BP2T) and its cyano-substituted derivative (BP2T-CN). Strong electron-withdrawing cyano-groups in BP2T-CN transform the p-type BP2T into n-type. Photoluminescence and electroluminescence from their bilayered films dominantly result from the BP2T-CN layer since the lying molecular orientation of BP2T-CN facilitates surface emission while the standing orientation of BP2T is not suitable for the device configuration. The current density and electroluminescence intensity are considerably increased by carrier doping with MoO3 and Cs2CO3 into the BP2T and BP2T-CN films, respectively.