This Small Business Innovation Research Phase I project seeks to demonstrate ultra high efficiency quantum dot light-emitting diodes (QD-LEDs) using a top-emitting structure and micro-lens array for display applications. Two key challenges will be addressed. First, a novel top-emitting structure will be explored based on the previous efficient bottom-emitting QD-LEDs. Use of top-emitting structure removes light trapped through the wave-guide mode within the glass substrate, which improves light out-coupling. A micro-lens array will be applied on top of the QD-LEDs to further enhance the light extraction. The project will focus on a number of innovative approaches. Micro-lens arrays will be fabricated using a novel stamp printing method. A small size micro-lens along with a top-emitting structure will minimize the pixel blurring effect induced by the conventional out-coupling micro-lens. Secondly, high refractive index material will be used to fabricate a micro-lens to match the refractive index of the transparent electrode, hence improving light extraction efficiency.
The broader impact/commercial potential of this project lies is to enable the commercialization of QD-LED displays, solid-state lighting and other applications. QD-LEDs provide intrinsically higher color purity compared to LCD or organic light-emitting diode (OLED) technology and are suitable for display applications. However, current QD-LED solutions suffer from lower efficiency compared to LCD and OLED. The company?s innovative nanomaterials and device architecture has enabled very efficient bottom-emitting QD-LEDs with high external quantum efficiency. Additionally, the multi-layer structure in the company?s QD-LED are deposited through solution processing, which reduces the cost significantly. It is expected that a better performing and substantially less expensive QD-LED will quickly gain considerable market share in a $60B market that ships over 1.5B units a year.
The objectives of this SBIR project was to develop fundamental understanding and new technological processes to produce quantum dot (QD) light emitting diodes(LEDs). Quantum dots are collections of approximately 800 to 1200 atoms. The properties of QDs are critically dependent upon their diameter and composition. Therefore the process of synthesizing quantum dots is extremely critical to success in demonstrating bright, efficient, stable QD-LEDs. The external quantum efficiency, EQE, but is one major of the efficiency of the devices. In this project, we demonstrated for the first time EQEs > 10% for all three colors (red, green and blue). In addition we demonstrated the current efficiencies of green emitting devices was >63 cd/A, which matches the efficiencies reported for organic light emitting diodes (OLEDs). Synthesis of bright, efficient and stable QDs was achieved as a result of this project.Two patents were filed to protect this information. Formation of micro lenses on the glass substrate extracted twice as much light from the QD-LEDs, resulting in further improvement of brightness and efficiency. The QD -- LEDs were used to fabricate 2 x 2 mm2 pixel passive matrix displays, as well as 4.3 inch, 480 x 800 pixel, active matrix monochrome (green and red is) displays. Finally, devices containing red, green, and blue emitting quantum dots were shown to produce white light upon application of a voltage. The result of this Phase 1 SBIR study will be sunlight readable, cheap, energy-efficient full color displays for the general public.
