This invention presents a new route to the fabrication of multilayer heterojunction devices useful for large and small, multicolored display applications by means of molecular self-assembly techniques. The technology addresses major coating issues in organic light-emitting diode (OLED) construction, and promises improved device performance and stability. Abstract ADVANTAGE Devices with uniform conformal layers, high light generation efficiency, emission wavelength control, and enhanced electrical, mechanical, and chemical stability are indicated. Significant cost benefits for OLED manufacture should result. SUMMARY OLEDs based on polymers or small molecules offer significant potential for applications in flat panel displays due to their high luminescent efficiency, low driving voltage, large viewing angle, light weight, simple device fabrication and potential low cost. Microfabrication of OLED devices and pixel arrays is essential for high-resolution display applications. Polymer based electroluminescent (EL) devices employ spin-coating techniques for layer deposition. This approach is disadvantaged by poor layer thickness control, interlayer diffusion, pinholes, and inability to produce thin layers necessary for efficient light collection and low d.c. driving voltages. Small molecule based devices employing vapor deposition overcomes many of the above problems but does not efficiently coat anode edges and corners, has limited conformal coverage and uncertain multilayer mechanical stability. This invention employs molecular self-assembly techniques, to overcome these coating difficulties. Covalently coupling the anode / hole transfer layer (HTL) / electron transfer-emissive layer (ETL/EML) / cathode material interfaces with molecular capping components affords devices with (1) uniform conformal layers at the nanometer scale, (2) high light generation efficiency at relatively low driving voltage, (3) emission wavelength control and (4) enhanced electrical, mechanical, and chemical stability. OLED multilayer structures (50 nm TPD hole transport layer, 60 nm AlQ electron transport/emissive layer, 100 nm Al cathode) were prepared by vapor deposition, employing the molecular capping materials at each interface, on patterned ITO / glass substrate. Typical performance metrics exhibit, light output: 90,000 cd/m², forward external quantum efficiency: 5+ %, luminous efficiency; 18+ lm/W; thermal stability: unaffected by cycling at 90°C. Use of the self-assembling molecular capping agents suggest improved OLED performance at reduced fabrication cost. STATUS U.S. Patents 6,586,763 and 7,094,121.
|State||Published - Sep 10 2009|