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.

Benefit

Low cost and simple to manufacture

Provides heat and water resistance to display applications (up to 180 C)

Market Application

Highly efficient LED down-converters or emitters for displays and solid-state lighting

Lasers and chemical sensors

High-efficiency active absorbers or passive luminescent concentrators for solar photovoltaics

Non-linear optical/photoconductive devices

Optical Display System Offers Enhanced Resolution for Heads-Up Displays

Abstract

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.

Technical Details

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.

Benefit

Enhances display resolution without expensive components

More reliable due to no moving parts

Easier to implement than other systems

Market Application

3D displays

Head mounted AR and VR displays

Ultra-Stable Deep-Dyed Perovskite-Polymer Composites as Tunable Downconverters

Abstract

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:

Perovskite precursors
Solvents
Polymer substrates that swell when brought into contact with the solvents and deswell when the solvents are removed.

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.