High-efficiency and color-stable warm white organic light-emitting diodes utilizing energy transfer from interface exciplex

Abstract We demonstrate high-efficiency warm white organic light-emitting diodes (WOLEDs) with an interface-exciplex-forming structure of hole-transporting 1,3-Bis(carbazol-9-yl)benzene (mCP) as electron-donor and electron-transporting 4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-(pyridin-3-yl)pyrimidine (B3PyMPM) as electron-acceptor. The exciplex can be formed effectively at the interface of mCP/B3PyMPM due to the excellent charge-transporting properties of mCP and B3PyMPM and the large energy-levels offset of mCP/B3PyMPM interface, and then its energy transfers to the low-lying triplet states of the blue TADF fluorophors or yellow phosphors. As a result, a maximum power efficiency (PE) of 79.2 lm/W and maximum external quantum efficiency (EQE) of 22.3% were achieved from the warm WOLED. The key factor for such high efficiency WOLED is believed to be from the effective harvest of triplet excitons of the interface-exciplex via reverse intersystem crossing process (RISC).