PeroLED Platform

One extremely promising technique to expand the colour gamut of displays is to use perovskite light emitting materials. Perovskite materials are defined by their unique crystal structure of ABX₃ where A and B are cations of different sizes, and X is an anion that bonds to A and B.

Excyton has developed a strong patent portfolio relating to the adoption of Perovskite LEDs (PeLEDs) in electronic displays. The patent portfolio covers perovskite ink formulations, device architectures, manufacturing methods and display designs.

Excyton has a particular focus on fabricating PeLEDs by inkjet printing and vacuum drying.

State-of-the-art displays, such as those in smartphones, tablets, watches, laptops, monitors and televisions are limited by their colourfulness. They can only render up to approximately 52% of colours visible to the human eye (as defined by the CIE 1931 (x, y) chromaticity diagram). The remaining colours are absent. This hinders the ability of displays to appear true to life and limits user experience. This is depicted in the chromaticity diagram, where only those colours contained in the “State of the Art” triangle can be rendered by state-of-the-art displays of today. This is the DCI-P3 colour gamut.

To address this shortfall, new standards have been introduced by ITU-R Recommendation BT.2020 (commonly known as BT. 2020 or Rec. 2020). These standards require displays of the future to render at least 76% of colours visible to the human eye. This is the Rec. 2020 colour gamut. This is depicted in the chromaticity diagram, where all colours contained in the “Rec 2020” triangle must be rendered for a display to meet Rec. 2020 standards. Perovskite LED technology provides a unique solution to enable displays to meet Rec. 2020 standards.

Perovskite Light Emitting Materials

Perovskite materials are extremely promising for light-emitting applications owing to strong electroluminescent properties and unrivalled high colour purity that can be tuned across the visible spectrum. Colour purity arises because light emission from the perovskite crystal structure is generally independent of variation in crystal dimensions. This enables perovskite materials to emit light with narrower emission spectra than quantum dots in QLED displays. Perovskite light emitting materials therefore provide a path to improve on the state-of-the-art and expand the colour gamut of displays.

Perovskite light emitting materials may be Photoluminescent or Electroluminescent and may be adopted in several different display architectures.

Photoluminescent

Enhancement Films

Photoluminescent perovskite materials may replace or complement conventional quantum dots in the enhancement film of liquid crystal displays (LCDs) to further expand colour gamut. This low-cost approach leverages existing LCD manufacturing infrastructure.

Colour Conversion Layers

Photoluminescent perovskite materials may be patterned directly on top of the individual pixels of an LCD, Micro-LED (µ-LED) or OLED displays. Patterning may be by inkjet printing or photolithography. This architecture is potentially more efficient than using Enhancement Films.

Electroluminescent

Perovskite Light Emitting Devices

Electroluminescent perovskite materials may be adopted in Perovskite Light Emitting Devices (PeLEDs). The red, green or blue pixels of a display may be individually patterned PeLEDs that emit light directly without the need for colour filters or colour conversion layers. This architecture is potentially more efficient than using Enhancement Films of Colour Conversion Layers. Excyton has developed technology and a patent portfolio with particular focus on electroluminescent perovskite materials and PeLEDs.

The general device structure of a PeLED is similar to that of an OLED or an electroluminescent QLED. An emissive layer is sandwiched between two electrodes with intermediate layers used to optimize charge balance and recombination within the device. For a PeLED the emissive layer comprises perovskite material, whereas for an OLED the emissive layer comprises organic material, and for a QLED the emissive layer comprises other quantum dot material. This synergy in device structure helps to greatly accelerate development of PeLEDs.

The emissive layer of a PeLED may comprise perovskite light emitting material in several different configurations: Two-Dimensional (2D), Three-Dimensional (3D), Quantum Dot (QD) and Multiple Quantum Well (MQW). The most efficient PeLEDs comprise perovskite light emitting material in either QD or MQW configurations.