High Performance Substrate Embedded Microgrids for High Efficiency, Flexible Organic Light Emitting Diodes

Indium tin oxide (ITO) films are currently the most widely used transparent conductor in optoelectronic applications. However, ITO suffers from several major technological and economic limitations for large area applications such as inadequate performance, high cost, and brittleness. The primary objective of this Small Business Technology Transfer (STTR) Phase I/Phase II project is to develop the scalable printing of high-performance substrate embedded metal microgrids as a transparent conductor for large area optoelectronic applications. In Phase I of this grant, we were able to demonstrate the fabrication of substrate embedded metal microgrids with vastly superior performance to ITO. We fabricated metal microgrids with transmission over 90% in the visible range and sheet resistance less than 1 /square with all processing at low temperatures (< 120 C). We demonstrated particle-free inks with an industry-best conductivity of 30 - 90% of bulk silver conductivity that are curable at < 120 °C. We also demonstrated the ability to create 3.5 mm width gridlines that are invisible to the naked eye and large area metal grid patterning on glass over 7 cm 7 cm. The approach for Phase II will be to work with various industrial partners to meet the performance needs of specific large area optoelectronic applications such as touch sensors, displays, electromagnetic interference (EMI), and organic light emitting diode (OLED) lighting. The technical tasks of Phase II are to (1) address scale-up and manufacturing challenges, (2) create invisible metal grid lines for large area displays, (3) demonstrate metal grids for EMI shielding, and (4) demonstrate integrated substrates for OLEDs. The results of this work will target the commercial applications of large-area touch sensors, displays, EMI shielding, and OLED lighting. This proposed substrate embedded microgrids are a new disruptive technology that vastly exceeds the performance of ITO, the standard for commercial transparent conductors. The main innovation of the proposed technology is that metal grids with high performance can all be printed at low temperatures with high throughput directly into large area substrates. Grids with small widths ( 5 mm) and large thicknesses (> 1 mm) can be printed over large areas (> 1010 cm).