Use of space interlayer in phosphorescent organic light-emitting diodes to improve efficiency and reduce efficiency roll-off

Typical phosphorescent organic light-emitting diodes (PhOLEDs) encounter efficiency roll-off problems and detrimentally degrades the device performance for practical applications particularity at high-brightness lightening. Here, we report high efficiency and reduced efficiency roll-off PhOLEDs by employing both 4,4', 4 "-tris-(N-carbazolyl)-triphenylamine (TCTA) and 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) as transporting, hosting and space interlayer (SIL) materials. The use of SIL blending TCTA into TPBi enables the current efficiency roll-up from 57.8 to 60.1 cd A(-1) with luminance increasing from 10.0 to 1143.0 cd m(-2). In particular, the current efficiency drops < 10% from 1143.0 to 5020.0 cd m(-2). In addition, the red-emitting sensitized dye further demonstrates that the SIL is dominant in expanding the dual exciton formation zone and suppressing efficiency roll-off. Also, the hole/electron balance can be manipulated by adjusting the doping ratio of the two materials in the SIL.