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Biologically Driven High-Resolution Assembly of Flexible Light-Emitting Display


OUSD (R&E) MODERNIZATION PRIORITY: Biotechnology, Microelectronics TECHNOLOGY AREA(S): Electronics, Materials/Processes OBJECTIVE: Develop a biology-based approach to assemble precisely structured arrays of pixels comprised of quantum dots for colorful, efficient, and flexible electroluminescent light-emitting displays DESCRIPTION: Inorganic quantum dot (QD) nanoparticles exhibit uniquely tunable optoelectronic properties [1]. Their use in electroluminescent films will enhance capabilities of light-emitting diodes (QD-LEDs), which perform crucial functions in defense and personal electronic devices. QD-LED displays, such as those in computer monitors, will deliver more colorful, high-resolution images, operate at higher efficiencies, and enable flexible or bendable device configurations [2]. QD-LEDs are comprised of two-dimensional periodic pixel arrays with rapid response rates. Each full-color pixel consists of distinct QDs that assemble into red, green, and blue (RGB) constituent sub-pixels. Although QD-LEDs show promise, they require novel fabrication approaches to precisely pattern QD pixels and optimize performance. Spin-casting cannot pattern microscale multicolor pixels without cross-contaminating distinct light-emitting QDs. Top-down photolithography may leave behind photoresist processing residue that impedes charge transfer. Emerging methods, such as inkjet printing, are expensive and have not yet surpassed performance levels offered by LCD and OLED competing technologies [3]. Synthetic biology enables novel control over engineering of peptides and microbes. Their finely tuned interactions with QDs may enable the bottom-up assembly of high-resolution patterns with tunable electronic and photonic properties [4]. Previously, DNA or protein biopolymers have been used to assemble inorganic nanomaterials into functional electronic components [5]. DNA scaffolds have facilitated self-assembly and patterning of plasmonic materials and carbon nanotubes [6, 7]. Conductive biomolecules, such as mesoscale silk fibroin networks, may 1) organize inorganic nanoparticles into periodic two-dimensional arrays, and 2) facilitate electronic conductivity through optoelectronic material networks [8]. This topic seeks to demonstrate the feasibility of using customizable biopolymers to fabricate novel, flexible QD-LEDs that exhibit full RGB colors (emission wavelengths: red: 630 nm; green: 530 nm; blue: 450 nm). This effort aims to develop the necessary biological tools to pattern externally synthesized inorganic QDs into pixel arrays that function as electroluminescent light-emitting displays. Performers will utilize peptides, DNA scaffolds, and/or other biological tools to arrange QDs into arrays of microscale pixels (containing RGB sub-pixels). Performers will use QDs of their choosing (to include commercially available materials). This program encourages use of synthetic biology tools to optimize particle arrangement approaches. Importantly, this effort will directly contrast the bio-based strategy against state-of-the-art nanofabrication approaches that assemble functional QD-LEDs. This program will culminate in a demonstration of a functional QD-LED display at least 2.5 inches (6.35 cm) wide. A bio-driven approach will assemble QDs into its electroluminescent layer. Performers will demonstrate a conventional stacked film configuration of QD-LEDs: electrodes, electron and hole charge carrier transport layers, the luminescent QD layer, and an external protective coating. Performers will choose the materials and assembly methods that deliver the required final prototype functionality. The resulting device will demonstrate a high pixel resolution [> 3000 pixel per inch (ppi)] that will exhibit the full RGB color spectrum. Biologically- assembled electroluminescent QD-LEDs will operate with > 25% external quantum efficiencies (EQEs). The device will reliably operate in ambient environments for extended time periods while maintaining high luminosity. The final QD-LED will demonstrate repeated flexibility and bendability for foldable or curved light-emitting displays. PHASE I: Develop a biologically-driven approach that assembles QDs into a pixelated two-dimensional film, which, with an externally applied electrical current, functions as a proof-of-concept electroluminescent QD-LED. Phase I prototype deliverable will emit monochromatic visible light (wavelength within the 450 – 700 nm range). The film should be at least 1 cm wide and can assume a rectangular or circular shape. The biopatterning technique will yield rectangular-shaped pixels with a 100 pixel-per-inch (ppi) resolution or greater, making each pixel 250 µm wide. Performers will need to fabricate necessary electrode and carrier injection layers that will complement the patterned QD pixels and enable electroluminescent operation of this proof-of-concept prototype. Physical elements used for biopatterning must be either compatible with (functionally integrated into) these layers, or fully removed from the film following completion of their intended QD assembly function, to prevent any detrimental interference with QDLED operation. Schedule/Milestones/Deliverables Phase I fixed milestones for this program should include: • Month 2: Deliver a report that identifies the selected biological system(s), as well as the inorganic QDs, that will be integrated to form ordered pixels and arrays. Demonstrate biocompatibility of proposed biological systems with targeted QDs. • Month 4: Demonstrate proof-of-concept ability to utilize the selected biological system(s) to organize QDs into films. Deliver a summary of complementary electrode and charge carrier materials, synthesis methods that will assemble them in conjunction with the QD films to exhibit electroluminescence, and experimentally-corroborated proof of compatibility of these device components with bio-patterned QD films. • Month 6: Demonstrate the results and a detailed description of the employed methodology to use selected biological system(s) in order to arrange QDs in an array (of regularly spaced rectangles [pixels]) with an overall array length of ≥1 mm and a width of ≤250 µm of each pixel. • Month 8: Document the ability to use biology to pattern a 2-dimensional array with equal pixel size and close-packed spacing between QDs in both x and y directions. • Month 10: Develop and test a proof-of-concept multilayer assembly (electrodes, carrier charge layers, and luminescent QD film) that is electronically conductive, optically transparent, and utilizes the selected biological system(s) to organize/pattern a functional electroluminescent QD layer (activated with an applied electrical current). • Month 12: Final Phase I Report that summarizes the overall approach and provides a description of the composition and operation of a proof-of-concept device architecture that uses a biological system to assemble QDs into a monochromatic, electroluminescent QD-LED. Its geometric configuration and mode of operation is expected to parallel that of conventional LED (such as an LED or OLED). Upon application of an external electrical current, the prototype will emit visible light perceptible to the naked eye. The LED will have a diagonal width of 1 cm or greater, with a luminescent layer comprised of rectangularly-shaped pixels, each with a side length ≤250 µm. The screen resolution for the Phase I prototype will be at least 100 pixels per inch (ppi). Test data should include device operational lifetime analysis (hours vs. luminosity and/or hours vs. quantum efficiency). PHASE II: Phase II Base: Develop, test, and demonstrate a biology-driven approach to assemble QDs into a high-resolution, full-color, flexible electroluminescent light-emitting display. Performers are expected to expand beyond the capabilities of the proof-of-concept prototype demonstrated at the end of Phase I and develop a device that meets or exceeds performance found with commercially available LEDs, such as those in screens of personal electronics (target device performance is described below). Performers must benchmark their approach against comparable QD-LED fabrication methods used in conventional manufacturing and demonstrate technical and commercial advantages of their bio-based approach. The QD-LED demonstrated at the end of Phase II must employ the bio-based approach to organize tri-color quantum dot pixels exhibiting RGB colors into a two-dimensional electroluminescent display film. The QD-LED display prototype must be at least 1 inch (2.54 cm) wide and exhibit a resolution of 3000 pixel per inch (ppi) or higher (7200 x 7200 pixels comprising the 1-inch-wide display). The display must have a luminosity of 2000 cd/m2 or higher. The electroluminescent quantum dots patterned into the QD-LED must operate with an EQE of at least 20%. Resulting QD-LED prototype must emit light for at least 500 hours without decaying in luminosity by more than 5%. Packaging of the prototype must allow it to operate in real-life environments that are common for conventional electronics (i.e. outside of an inert gas-filled glovebox). The final fully-functional QD-LED prototype should be capable of repeated bending that expands the viewing angle to above 90 degrees. Schedule/Milestones/Deliverables Phase II Base fixed milestones for this program should include: • Month 2: New Capabilities Report, which identifies additions and modifications that will be researched, developed, and customized for enhancement and optimization of the Phase I system to enable Phase II goals to be met. • Month 4: Report on fabrication and testing of a proof-of-concept prototype electroluminescent QD-LED. The display should be comprised of bio-patterned QDs that operate with an EQE of 10% or higher, and a luminosity of 100 cd/m2 or higher. • Month 6: Report that describes the state-of-the art manufacturing method that performers will use for comparison against their bio-based QD-LED assembly approach. The comparison must include experimental data that describes this approach’s implementation and methodologies, as well as analysis of the method’s costs and resulting QD-LED performance. • Month 9: Experimentally demonstrate mechanical flexibility of the bio-based patterned QD layer and its ability to repeatably bend without breaking or affecting its electroluminescent performance. Demonstrate ability to modify bio-based QD patterning to control inter-pixel spacing to minimize image distortion during bending of QD-LED film. • Month 12: Report on the feasibility of the bio-based patterning of an electroluminescent film comprised of pixels of two distinct colors (e.g. red and blue, green and red, or green and blue). Each pixel must be of identical size, and each color sub-pixel must be of identical size and luminosity. The pattern must retain regular periodicity throughout the display, which must be 1 cm or greater in width. The film that incorporates these pixels must exhibit these colors, and their combinations must be clearly visible to the naked eye of a human observer. • Month 15: Report on the feasibility of the bio-based patterning of an electroluminescent film comprised of RBG pixels, with the same metrics for periodicity, pixel size, and observation capabilities as stated in month 12. • Month 18: Demonstration of QD-LEDs that enable electroluminescent operation of RGB QD pixels with EQEs of at least 15%. Improve scalability of approach and deliver a light-emitting display with a width of at least 2 cm. Develop and demonstrate packaging of the display that enables its operation in ambient environments, to include oxygenated atmosphere, varying humidity levels, and room temperature. Assess operating lifetime of the display, including luminosity vs. timeline during constant operation, and achieve a minimum of 250 hours without decaying by more than 10%. • Month 21: Report that comprehensively benchmarks the manufacturing method and performance of the bio-patterned QD-LED demonstrated in Month 18 against the SOA non-bio-based QD-LED synthesis approach. The report needs to directly compare the technical performance of the two methods, including luminescence, pixel resolution, external quantum efficiency, and operating lifetime. Experimental comparison of the two prototypes must analyze identically sized bio-based QD-LED and non-bio-biased (SOA) QD-LED test coupons. • Month 24: Final Phase II report that documents the fabrication and performance of the display, including structure of fully assembled functional QD-LEDs, biological assembly platforms, methods used to manufacture the display, the physical characteristics of the resulting device, and its performance testing results (including performance documented with photography/videography, as well as a description of methods and formulas used to calculate the key metrics that assess its performance). Report must include data that demonstrates the following: 1) bio-assembled electroluminescent display that clearly demonstrates fully visible RGB colors; 2) QDs in the display exhibit an EQE of at least 20%; 3) display width of 1 inch or greater; 4) luminosity of at least 2000 cd/m2; 5) lifetime assessment that demonstrates a luminosity decay of less than 5% after 500 hours of operation; 6) resolution of 3000 ppi or higher; 7) mechanical flexibility that enables a viewing angle of at least 90 degrees. Phase II Option: The Phase II Option 12-month period aims to further scale up the size of the bio-patterned QD-LED prototype, improve its technological capabilities and versatility performance metrics, and advance its integration into DoD or commercial prototypes. Performers must develop capabilities to demonstrate high-resolution images and video on screens of QD-LEDs and scale-up dimensions of the technology to levels of targeted end products (such as those comparable to state-of-the-art mobile telephones or computer tablet screen) without a decrease in performance. Three prototypes will be delivered to the government for testing and analysis. Schedule/Milestones/Deliverables Phase II Option fixed milestones for this program should include: • Month 2: Demonstrate the ability to exhibit a series of 5 still RGB images (with > 3000 ppi resolution) from data files on the screen of the display. • Month 4: Demonstrated rapid color switching of QD color (turn pixel on/off) and color recycling with a fast refresh rate (of at least 2000 Hz) in the full-color QD-LED prototype. • Month 6: Deliver three prototypes to U.S. government laboratories for testing and analysis. • Month 9: Exhibit ability to scale up bio-based QD-LED to a width of 6.35 cm or more. Demonstrate ability of the prototype to repeatedly bend back and forth by 45 degrees or more for at least 100 cycles while operating without breaking. • Month 12: Improve EQEs of QDs to 25%. Improve luminosity to over 10,000 cd/m2. Demonstrate continuous operation lifetimes of at least 2,000 hours with a luminosity decay of less than 5%. Demonstrate an ability to exhibit a 30-second full-color video file on the display (with > 3000 ppi resolution). PHASE III DUAL USE APPLICATIONS: Electroluminescent QD-LED are highly desired for colorful, efficient, and flexible consumer electronics. Use of biologically-driven synthesis approaches that offer greater precision can enhance the performance capabilities of resulting devices over existing quantum dot technologies synthesized using conventional means. Precise patterning of inorganic nanoparticles using developed biological tools, such as microbes and biopolymers, may enable a wide variety of high-performance electronics that can be produced domestically using more environmentally friendly and less expensive methods. Non-defense applications of technologies developed under this program may include flexible displays for mobile phones and televisions, wearable personal electronics, smart textiles, antennas that receive microwaves or radio waves, circuitry components such as resistors and capacitors, and biomedical sensors and implants. REFERENCES: 1. [1] García de Arquer, F.P., et al., Semiconductor quantum dots: Technological progress and future challenges. Science, 2021. 373 (6555): p. eaaz8541. 2. [2] Dahad, N., Quantum Dots to Shrink MicroLED Display Pixels, in EE Times. 2019. 3. [3] Song, J.-K., et al., Materials and devices for flexible and stretchable photodetectors and light-emitting diodes. Nano Research, 2021. 14 (9): p. 2919-2937. 4. [4] Shin, J., et al., Programming Escherichia coli to function as a digital display. Molecular Systems Biology, 2020. 16 (3): p. e9401. 5. [5] Sun, Q., et al., Highly Efficient Quantum-Dot Light-Emitting Diodes with DNA−CTMA as a Combined Hole-Transporting and Electron-Blocking Layer. ACS Nano, 2009. 3 (3): p. 737-743. 6. [6] Mann, V.R., et al., Controlled and Stable Patterning of Diverse Inorganic Nanocrystals on Crystalline Two-Dimensional Protein Arrays. Biochemistry, 2021. 60 (13): p. 1063-1074. 7. [7] DeLuca, M., et al., Dynamic DNA nanotechnology: toward functional nanoscale devices. Nanoscale Horizons, 2020. 5 (2): p. 182-201. 8. [8] Fernández-Luna, V., et al., Biogenic fluorescent protein–silk fibroin phosphors for high performing light-emitting diodes. Materials Horizons, 2020. 7 (7): p. 1790-1800. KEYWORDS: Light-emitting display, quantum dot, biological fabrication, synthetic biology, flexible electronics
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