Investigation on OLEDs efficiency roll-off with interfacial charge storage and their time-resolved emission spectra

Abstract

Abstract Organic light-emitting diodes (OLEDs) are the next generation technique of display and lighting, confronted with the bottle-neck problem of OLEDs efficiency roll-off. The nature of luminescence and efficiency roll-off of OLEDs are processes of electrons and energy, during which charge injection and storage play important roles. In order to study the mechanism of OLEDs efficiency roll-off with interfacial charge storage, organic light-emitting devices with Ir(ppy)3 doped CBP as the light-emitting layer were prepared, and PMMA layers of 5 nm, 6 nm, 8 nm and 9 nm were inserted as charge storage layers to control hole injection and hole accumulation. The OLEDs efficiency roll-off is obvious with the increase of the current density. The storage of t he interfacial charges is analyzed by transient electroluminescence measurement. Luminescence spikes occur at both forward and reverse turn-off voltages, which is caused by electron diffusion and trap carriers release, respectively. The time-resolved emission spectra prove the relationship of interfacial charges and exciton quenching. The OLEDs efficiency roll-off is positively correlated with the interfacial charge storage especially at low current density. This is due to the effect of the accumulation of the interfacial charge especially under unbalanced charge injection of OLEDs, which is of importance to improve the OLEDs performance and to decrease the OLEDs efficiency roll-off in industry.