Proposed energy diagram of the green OLED and molecular structures of the bipolar material ( -CzOXD) and three phosphorescent dopants. Note that the numbers indicate the respective highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO, respectively) energies relative to the vacuum.
(a) Current and power efficiencies as a function of voltage for the green OLED with the structure of indium tin oxide (ITO)/ (5 nm)/ -CzOXD (35 nm)/ -CzOXD: 9 wt % (30 nm)/ -CzOXD (35 nm)/LiF/Al. The inset gives the normalized EL spectrum of the green device at a voltage of 9 V. The CIE coordinates are calculated to be (0.34, 0.62). (b) Voltage-current density-luminance characteristics of the green device.
(a) Current density-voltage characteristics of the hole-only devices with different organic layer thicknesses of 100 nm (square), 190 nm (circle), 300 nm (up triangle), and 350 nm (down triangle). The solid line represents the simulated current density for SCLC with a filled dependent mobility. The inset plots the current density at a constant electric field of vs the -CzOXD thickness. The solid line shows a linear dependence with correlation coefficient . (b) Current density-voltage characteristics of the electron-only devices with different organic layer thicknesses of 100 nm (square), 200 nm (circle), 300 nm (up triangle), and 350 nm (down triangle). The solid lines indicate the fitting to the Eq. (2) with and trap density . The inset plots the dependence of the applied voltage V on at a constant current density of . The solid line shows a linear dependent with correlation coefficient .
The relationship of hole and electron mobility vs the electric field. The hole mobility is comparable to the electron mobility at field of .
Current efficiency vs distance between the -doped -CzOXD and the anode in the structure shown inset. The inset depicts the schematic cross-section of the test structures of (5 nm)/ -CzOXD ( nm)/ -CzOXD: 9 wt % (30 nm)/ -CzOXD /LiF/Al, with , 20, 35, 50, and 60.
Current density-voltage characteristics of hole- and electron-only devices with structures of (5 nm)/ -CzOXD (35 nm)/ -CzOXD or dye doped -CzOXD (30 nm)/ -CzOXD (35 nm)/ /Al (Top) and Al/LiF/ (5 nm)/ -CzOXD (35 nm)/ -CzOXD or dye doped -CzOXD (30 nm)/ -CzOXD (35 nm) / /Al/LiF/Al (Bottom), respectively, where the dopants are (a) 9 wt % , (b) 6 wt % , and 5 wt % . (c) Hole and electron current in 9 wt % -doped device.
EL spectra of the series of green devices in which a thin slab of 9 wt % : -CzOXD locates at various distances from the anode at a constant current density . The inset is an enlarged image of EL intensity at the wavelength from 400 to 495 nm, showing the weak blue emission from -CzOXD.
A summary of device characteristics: turn-on voltage , maximum external quantum efficiency , maximum current efficiency , maximum power efficiency , CIE, and brightness . , , and .
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