Researchers at CEA-Leti (Université Grenoble Alpes) have developed green and red-emitting thin-film perovskite color conversion layers (CCLs) using pulsed laser deposition (PLD), targeting GaN-based microLED displays for AR/MR applications.
GaN-based microLEDs offer a superior image quality with high dynamic range and saturated colors for AR/MR glasses, smartwatches, and more. However, achieving full-color pixels remains difficult since conventional InGaN/GaN multi-quantum wells (MQWs) emit a single color based on indium content - blue (~10% In), green (~25% In with lower efficiency), or red requiring separate InGaP materials. Mass-transfer works for larger displays but fails for microdisplays needing sub-1μm pixel pitches, where growing all three colors adjacently is still years from production.
An alternative uses CCLs to down-convert blue microLED emission via photoluminescence. Quantum dots (QDs) like CdSe (FWHM 28-32 nm, high PLQY) or cadmium-free InP (FWHM 35-37 nm, PLQY 95-100%) provide good gamut but suffer low absorption (~10^3 cm⁻¹), requiring 5-10μm thicknesses that prevent <5μm patterning and limit AR/MR viability (needing 100,000-1M nits brightness, <1μm pitches). Perovskite QDs improve this to ~3μm, but still fall short.
Inorganic halide perovskites (CsPbBr₃ for green, CsPbI₂Br for red) offer direct bandgap, high absorption (~10⁵ cm⁻¹), narrow emission (FWHM 17nm at 516nm green, 31nm at 640nm red), and tunable composition. Deposited via PLD on 200mm wafers at room temperature, they outperform InP QDs in purity and offer high uniformity. Theoretical microLEDs with these CCLs plus filters cover 90% of Rec. 2020 gamut (CIE: green 0.100,0.785; red 0.704,0.296; blue 0.140,0.048), with green needing minor wavelength shift via composition engineering.
At 450nm, absorption reaches 4.6×10⁴ cm⁻¹ (CsPbBr₃) and 6.4×10⁴ cm⁻¹ (CsPbI₂Br) – up to 20x higher than InP QDs - enabling 90% blue light absorption at just 500nm (green) or 360nm (red) thicknesses. This supports <1μm pixel pitches with and easy patterning.
In first experiments, CsPbBr₃ films maintain stable emission wavelength and FWHM from 0.06 to 715 W/cm² (375nm laser) - exceeding AR/MR needs (~1 W/cm² for 100k nits) by three orders of magnitude, proving to have high potential for low QD degradation under flux or moisture. Further testing is required to determine stability for longer time periods.
Anyone that wishes to contact the researchers at CEA Leti can reach out to the lead researcher, Dr. François Templier, at ftemplier@cea.fr.
