Research Terms
SPIE, Fellow; 2007 - present
IEEE, Fellow; 2004 - present
SID, Fellow; 2001 - present
OSA, Fellow; 1993 - present
Applied Physics Letters
Proposals, National Science Foundation
The University of Central Florida invention comprises tunable, flexible QLEDs and methods for configuring the devices for use in phototherapy and photobiomedicine as well as lighting displays and sensors. For example, the invention could be used to produce ultrabright, flexible QLEDs for low-cost, wearable, disposable, light-emitting bandages to treat oral cancer or diabetic wounds.
The UCF QLED device includes quantum dots (QDs) as emitters and a mixture of metal oxide nanoparticles and alkali metal compounds for simultaneous electron injection and hole blocking to achieve charging balance at high driving current conditions. It surpasses state-of-the-art OLED technology in peak luminance and electroluminescence efficiencies at high current densities. With the additional benefits of solution processability, record low power consumption, and structural compatibility with n-type transistor backplanes, the QLEDs offer great potential for photomedicine applications as well as next-generation display, lighting and optical sensors.
Technical Details: The inventive methods comprise depositing a layer of quantum dots (QD) to function as emitters and a layer comprising a mixture of metal oxide nanoparticles and alkali metal compounds to provide in its entirety. In various embodiments, the QLED light source includes a mixture layer of electron-injecting ZnO and a hole blocking Cs2CO3. Pure color red QLEDs of the invention, in rigid or flexible form factors, can be used to positively change phototherapy applications in dermatology, oncology, minimally invasive surgery, stroke, and brain disease, among other fields.
High driving current conditions can achieve brightness levels of more than l00,000 cd/m2. In one embodiment, UCF researchers achieved flexible QLEDs with a peak external quantum efficiency of 8.2 percent and a luminance of more than 20,000 cd/m2 at a low driving voltage of 6 V.
Partnering Opportunity: The research team is seeking partners for licensing, research collaboration, or both.
Stage of Development: Prototype available.
20.2: Ultra-Bright, Highly Efficient, Low Roll-Off Inverted Quantum-Dot Light Emitting Devices (QLEDs), SID Symposium Digest of Technical Papers, 46, DOI: 10.1002/sdtp.10462.
UCF researchers have developed a simple, cost-effective method of fabricating perovskite-polymer composite materials with high photoluminescence quantum efficiency, exceptional moisture insensitivity and long-term stability. The new process resolves the instability issues that occur when organic-inorganic hybrid perovskite materials are exposed to external stresses (such as heat, water, light and electrical fields). Using the new method, manufacturers can now create and use highly stable perovskites to produce low cost, reliable, high-performance products. For example, the method can be used to create displays that withstand harsh environmental conditions—until now, no other means have been available.
Technical Details
The new method uses a swelling-deswelling microencapsulation process to create solution-processable organic-inorganic perovskites (OIPs). The swelling-deswelling encapsulation method involves three components: perovskite precursors, solvents, and polymer substrates. The substrates swell when brought into contact with the solvents and deswell when the solvents are removed.
The method starts with a perovskite precursor solution. The solution is processed directly onto a polymer matrix using a solvent combined with a procedure such as spin coating, dip coating or slot die coating. The solvent penetrates the polymer matrix and causes swelling, which allows the perovskite precursors to enter the polymer. Afterward, the solvent is removed from the polymer matrix, leaving the perovskite precursors in the matrix to react and form perovskite nanocrystals. The polymer subsequently deswells, forming a barrier layer around the perovskite nanocrystals to create a stable perovskite-polymer composite. Numerous types of perovskites, solvents and polymers may be used, as long as the polymers swell and deswell when solvents enter and exit them.
UCF researchers have invented a novel display apparatus that resolves the low image resolution issues associated with augmented reality and virtual reality (AR/VR) heads-up systems. AR/VR display technology includes immersive video games and interactive 3D graphics. The new invention effectively doubles the resolution of head-mounted devices without requiring expensive or complex parts. One approach to resolving AR/VR low-resolution issues is to produce an offset to the display pixels using time-multiplexing (that is, displaying an image for the first frame, and then an offset image for the second, offset frame). However, such methods have only worked in projectors where the form-factor is not critical. Additionally, the methods use expensive birefringent crystals, moving shutters or complicated polarization systems, which are impractical for compact head-mounted displays. With the new invention, manufacturers can use the same image offset methods to provide high-resolution head-mounted AR/VR displays that are also optically and mechanically simpler, lighter and less expensive.
The invention for head-mounted displays encompasses a high-resolution optical system apparatus and methods for offsetting viewable pixels by a portion of a pixel width. The apparatus includes a programmable/controllable (virtual) image-generating component that synchronizes with an electrically switchable image offset component. For example, the image-generating component can be an LCD display that generates a polarized image output. The image-offset component can be a liquid crystal diffractive wave-plate that accepts output from the image-generating component. Using either direct voltage or the polarization of the displayed light, the system switches a displayed image between an offset and non-offset state to provide high-resolution output. For instance, by shifting an image by half a pixel width in one dimension faster than 25 hertz (cycles per second), the image resolution appears to increase.
Researchers at the University of Central Florida have developed a low-cost, simple deep-dyeing method that can convert a polyethylene terephthalate (PET) polymer matrix into ultra-stable luminescent perovskite-polymer composites (PPCs) that demonstrate water resistance and heat stability. Due to their excellent color tunability, color purity, and water-/photo-stability, the PPCs are usable in displays, solid-state lighting, or other applications. The invention addresses a growing demand for improved, cost-saving manufacturing techniques that produce displays encompassing a large color gamut and high photoluminescence efficiency. With the invention, solid-state lighting (SSL) systems can meet specific lighting requirements while at the same time reducing or omitting unnecessary or even damaging portions of the spectrum. Applications include optical down-converters or emitters for display and lighting or active absorber or passive luminescent concentrators for solar photovoltaics.
Technical Details
The UCF invention comprises methods for fabricating stable, highly luminescent perovskite-polymer composites. It includes a swelling-deswelling encapsulation method involving three components:
For example, a perovskite-precursor solution is prepared: PbBr2 and CH3NH3Br are combined with a molar ratio of 1:3 in dimethylformamide to yield MAPbBr3. The solution is processed directly onto a polymer matrix through spin coating, dip coating, slot-die coating, inkjet printing, spray coating, or cotton swab painting. Next, a solvent (such as dimethylformamide) penetrates the polymers, causing them to swell and absorb the perovskite precursors. Finally, the solvent is driven out of the polymer matrix (by baking at 25-120 degrees Celsius for 2-10 hours), leaving the perovskite-precursors within the polymer matrix to react and form high quality, well-dispersed luminescent perovskite nanocrystals.
As the polymer substrate deswells (shrinks back), it forms a coherent barrier layer around the perovskite nanocrystals. This barrier protects them from water and oxygen from the surrounding environment. The perovskite-polymer composites possess high optical qualities showing narrow emission peaks and high photoluminescence quantum yield (PLQY). Numerous types of perovskites, solvents, and polymers may be used if the polymers swell and deswell when solvents enter and exit them.
High color quality white-light generation was demonstrated using green emissive MAPbBr3-polymer composites and red CdSe-based quantum dots as down-converters of blue LEDs. The LEDs provided color gamut coverage of a record 95 percent of Rec 2020, the color standard for ultra-high definition (UHD) TVs.
Partnering Opportunity
The research team is looking for partners to develop the technology further for commercialization.
Stage of Development
Prototype available.
A deep-dyeing strategy for ultra-stable, brightly luminescent perovskite-polymer composites, Journal of Materials Chemistry C, 2021,9, 3396-3402, https://doi.org/10.1039/D1TC00042J
