Enhanced performances of planar heterojunction organic light-emitting diodes via diluting an n-type transporter into a carbazole-based matrix

Abstract

Electroluminescence originating from layer-to-layer charge transfer (LLCT) in organic light-emitting diodes (OLEDs) was early observed, whereas, the inferior performances limit their practical applications. In this work, we demonstrated an efficient approach to improve the overall performances of LLCT-based planar heterojunction OLEDs by simply diluting an n-type electron transport material into a carbazole-based matrix material to suppress excited-state quenching. As a result, an optimized device with a peak current efficiency of 41 cd A⁻¹ (corresponding to a maximum external quantum efficiency of 12.6%) exhibited significantly enhanced efficiencies and much higher brightness at high current densities in contrast to the control devices without a mixture layer. We illustrated that even with a similar narrow recombination region, it is feasible to achieve excellent fluorescent OLEDs with light emission originating from LLCT. We believe that this work should pave the way for developing high-performance LLCT-based OLEDs with a high efficiency, reduced efficiency roll-off and sufficiently large maximum brightness.