Quenching-enhanced shift of recombination zone in phosphorescent organic light-emitting diodes

We studied the influence of concentration quenching on exciton distribution and recombination in organic light-emitting diodes (OLEDs) with a neat fac-tris(2-phenylpyridinato-N, C2′) iridium (III) [Ir(ppy)3] emitting layer (EML). It has been found that electron overflow to the hole transport layer (HTL) at elevated currents was enhanced by quenching in the EML, leading to a broadened recombination zone. The maximum quenching of green phosphorescence occurred in OLEDs with 4 nm Ir(ppy)3 and correlated well with the strongest blue fluorescence from the HTL. The OLEDs emitted white light with an efficiency of 6.5 cd/A and a quantum efficiency twice as high as compared to similar OLEDs with an additional 4,4′,4″,-tris(N-carbazolyl) triphenylamine (TCTA) EBL.