Effect of Energy Level Gradient in Emitting Layer on Blue Organic Light-Emitting Diode

Herein, a series of blue organic electroluminescence devices arc fabricated with 4, 4',4 ''-tris(N-carbazolyl) triphenyl-amine (TCTA), N, N'-dicarbazolyl-3, 5-benzene (mCP), and 1, 3, 5-tri (m-pyridin-3-ylphenyl) benzene (TmPyPB) as the host materials. Owing to the different lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) energy levels of the host materials, a structure in the light-emitting layer (EML) with different energy level gradients is formed by changing the host materials and the number of EMLs. The effects of different EMI. structures on the performances of blue phosphorescent organic light-emitting diode arc investigated. Among them, the double light-emitting layer device Lambda 3 with the host materials of TCTA and mCP obtains the best performance, and the maximum current density, the maximum current efficiency, and maximum luminance arc 134.94 mA/cm(2), 40.28 cd/Lambda, and 12070 cd/m(2), respectively. Among all devices, device Lambda 3 also exhibits the characteristics of low turn-on voltage (3. 25 V) and low efficiency roll-off.