Printed Copper Grid Transparent Conducting Electrodes for Organic Light-Emitting Diodes

The transparent conductive electrode (TCE) is a key component of organic light-emitting diodes (OLEDs). High-resolution printed metal grids are a promising alternative to indium tin oxide (ITO). We present results for evaporated OLEDs with a printed copper (Cu) grid with line width below 3 μm. The use of a thick doped hole injection layer (HIL) prevented electrical shorts and resulted in good quality OLEDs with acceptable leakage current. We report a detailed analysis of the microscopic uniformity of light emission and compare the measured data with simulations based on finite element modeling (FEM) to investigate various factors that contribute to differences between the Cu grid OLED and ITO reference device. This insight resulted in design rules that enable a luminance of the Cu grid OLED that can potentially equal that of an ITO-based equivalent OLED by using a very fine pitch and narrow line width of 5 μm and 250 nm, respectively, within the capabilities of state-of-the-art printing technology.