ITO-free large-area organic light-emitting diodes with an integrated metal grid

We report on ITO-free large-area organic light-emitting diodes (OLEDs) fabricated on glass substrates comprising alpha-NPD as a hole transport layer (HTL) and coevaporated CBP:Ir(ppy)(3) as the emission layer. Indium-tin-oxide (ITO) was replaced with a conductive polymer electrode and an electroplated thick metal grid was used to improve the homogeneity of the potential distribution over the transparent polymer electrode. An electrical model of a metal grid integrated OLED shows the benefits of the use of metal grids in terms of improving the uniformity of the light emitted as the area of the OLED increases as well as the conductivity of the transparent electrode decreases. By integrating metal grids with polymer electrodes, the luminance increases more than 24% at 6 V and 45% at 7 V compared to the polymer electrode devices without a metal grid. This implies that a lower voltage can be applied to achieve the same luminance, hence lowering the power consumption. Furthermore, metal grid integrated OLEDs exhibited less variation in light emission compared to devices without a metal grid. (C) 2011 Optical Society of America