Aluminum has been extensively used as a conductor material in numerous electronic devices, including solar cells, light-emitting diodes (LEDs), organic LEDs (OLEDs), and thin-film transistors. However, its spiking surface and easy electromigration have limited its performance. To overcome this, a trace amount of nonprecious copper dopant has been proven effective in enhancing device reliability. Nevertheless, a comprehensive investigation regarding the effect of copper doping on the morphology at the aluminum conductor-organic interface is yet to be done. We had hence fabricated a series of green OLED devices to probe how copper doping affected the aluminum conductor, morphologically and electrically, and the corresponding device's efficiency and lifetime performance. We found 4 wt % copper doping to be highly effective in enabling a spike-less and smoother aluminum interface, which in turn enabled the fabrication of devices with much higher efficiency and lifetime. Specifically, the corresponding power efficacy at 1000 cd/m2 was increased from 32 to 42 lm/W and the lifetime increased from 75 to 263 h, an increment of 250%. Atomic force microscopy confirmed that the copper doping did help smooth out the conductor interface as deposited and reduce electromigration upon operation.
Keywords: OLED; efficiency; electromigration; lifetime; minor copper-doped aluminum cathode; spike-less.