Manuel Gensler & Bernd Richter & Lutz Deriks | Fraunhofer IAP, IPMS, ILT: How do solvent-free, photocrosslinkable quantum dot inks eliminate the coffee-stain effect and enable single-step thick cavity filling?
10:24 - 11:27
Other snippets from this talk
Summary of the clip:
How do solvent-free, photocrosslinkable quantum dot inks eliminate the coffee-stain effect and enable single-step thick cavity filling?
To maximise emission, the cavity must be filled as thick as possible, so the ink should not be dried. Conventional printing requires repeated passes to reach a 10-micrometre cavity thickness. Fraunhofer's solvent-free inks remove that multi-step constraint: the first printing step fills the cavity, and no drying step is wanted.
The key is a solvent which is photocrosslinkable: the solvent itself is the resin, with quantum dots inside. You print, fill up, everything remains liquid, then photocure it, and it is done. This is similar to photolithography but combined with printing. It enables single-step thick cavity filling without repeated printing passes.
On the large substrate, there is no coffee-stain effect because there is no drying, only photocuring. This yields filled cavities without coffee stain for the quantum dot layers, giving homogeneous emission. The quantum dots should also have high absorbance, not just in the UV. That combination addresses both thickness and uniformity in printed colour conversion.
In this short video, you can learn:
* A photocrosslinkable solvent acts as the resin, so printing, filling and photocuring replace repeated print-and-dry cycles.
* The solvent-free ink eliminates the coffee-stain effect because there is no drying step, only photocuring, yielding homogeneous quantum dot emission.
* A single print can fill a cavity to the required 10-micrometre thickness, and the quantum dots should have high absorbance beyond the UV.
📋 **Clip Abstract** Fraunhofer presents solvent-free, photocrosslinkable quantum dot inks for filling microdisplay cavities as thick as possible without drying. The solvent is the resin, so printing, filling and photocuring in one step avoids repeated passes to 10 micrometres and removes the coffee-stain effect, while the quantum dots need high absorbance not only in the UV.
About the speakers:
* Speakers: Manuel Gensler, Bernd Richter, Lutz Deriks
* Companies: Fraunhofer IAP, IPMS, ILT
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#QuantumDotInk, #PhotocrosslinkableResin, #SolventFreeInk, #CoffeeStainFree, #MicroLEDMicrodisplays, #QuantumDotColorConversion
This is a highlight of the presentation:
Integrated MicroLED Assembly and QD Colour-Conversion Technologies for Microdisplays
More Highlights from the same talk.
01:08 - 02:57
Why does combining blue microLEDs with quantum dot color conversion solve the major manufacturing and efficiency bottlenecks of native RGB displays?
Why does combining blue microLEDs with quantum dot color conversion solve the major manufacturing and efficiency bottlenecks of native RGB displays?
Quantum dot color conversion tackles a major manufacturing bottleneck in microLED displays. Producing an RGB microLED requires transferring red, green, and blue chips three separate times, which reduces yield. By using only blue microLEDs and performing color conversion on top, the transfer is performed once, greatly improving transfer yield. Additionally, LEDs of different colors have different driving voltages, whereas a blue-only backplane requires the same driving voltage for red, green, and blue after conversion, simplifying driving electronics.
Quantum dots also address efficiency and stability mismatches. Red and green quantum dots are far more stable than blue ones, which is directly opposite to microLEDs where blue emitters are most efficient. This creates a perfect match: the most efficient blue microLEDs are combined with more stable red and green quantum dots via color conversion. Even when using aluminum gallium systems for red microLEDs, especially at small chip sizes, the external quantum efficiency of red microLEDs is lower than for blue counterparts, reinforcing the benefit of quantum dot conversion.
The color performance of quantum dot conversion does not sacrifice quality. According to the speaker, in terms of color gamut, microLEDs and quantum dots are on par, so there is no issue not using quantum dots here. From the material perspective, there are actually three types of nanomaterials which can be used. These include cadmium-based quantum dots, which are mentioned as one of the options. The clip ends before the remaining two types and the specific properties of cadmium-based quantum dots are described.
In this short video, you can learn:
* Using color conversion with blue microLEDs avoids transferring red, green, and blue chips three separate times, improving transfer yield.
* A blue-only microLED architecture ensures the same driving voltage for red, green, and blue subpixels after color conversion.
* Blue microLEDs are most efficient, while red and green quantum dots are far more stable than blue quantum dots, yielding a complementary performance match.
📋 **Clip Abstract** Quantum dot color conversion solves key manufacturing and efficiency challenges for microLED displays by enabling a blue-only emitter approach, eliminating triple mass transfer and unequal driving voltages. Blue microLEDs are the most efficient, while red and green quantum dots are more stable than blue ones, creating an optimal match with color gamut on par with native RGB microLEDs.
About the speakers:
* Speakers: Manuel Gensler, Bernd Richter, Lutz Deriks
* Companies: Fraunhofer IAP, IPMS, ILT
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#QuantumDotColorConversion, #MicroLEDMassTransfer, #BlueMicroLEDs, #AluminumGalliumSystems, #Microdisplays, #QuantumDots
11:27 - 13:11
What material-level strategies can increase blue light absorption in ultra-thin quantum dot color conversion layers?
What material-level strategies can increase blue light absorption in ultra-thin quantum dot color conversion layers?
For quantum dots that absorb well in the blue, the clip presents two material approaches. A giant-shell cadmium system adds an outer shell acting like an antenna structure. At the relevant blue region of 465 nm for red 2020, increasing the quantum dot diameter strongly increases absorbance while keeping the same red emission. For indium phosphide systems, an alloying system can also raise absorbance at the relevant blue wavelength, yielding high absorbance in the material.
Higher absorbance enables a lower layer thickness until full color conversion of the blue backlight is reached. Because this is usually not enough at 10 nm already, an additional trick is required: scattering particles. The team developed stable inks with quantum dots and titanium dioxide scattering particles. Increasing the titanium dioxide amount in the ink and layer produces lower transmittance at lower layer thicknesses, because the optical density of the whole layer is further improved.
The lifetime of the quantum dot is another crucial issue. The clip says it can be tackled on the material side, again by the giant-shell approach. This connects directly to blue absorption: the same shell strategy that raises absorbance at blue wavelengths is also presented as a route for lifetime improvement. The discussion stops there in this clip, so the material-level trade-offs between shell diameter, emission wavelength, absorbance, and lifetime remain the practical challenge for ultra-thin quantum dot color conversion.
In this short video, you can learn:
* A giant-shell cadmium system adds an outer shell that acts like an antenna structure, increasing absorbance at the relevant blue region of 465 nm for red 2020 while keeping the same red emission.
* Indium phosphide systems can use alloying to increase absorbance at the relevant blue wavelength, yielding high absorbance and enabling lower layer thickness for full color conversion of the blue backlight.
* Because 10 nm is usually not enough, stable inks with quantum dots and titanium dioxide scattering particles improve optical density and lower transmittance at lower layer thicknesses, while the giant-shell approach also tackles quantum dot lifetime.
📋 **Clip Abstract** The clip outlines material-level strategies for boosting blue absorption in quantum dot color conversion: giant-shell cadmium systems with an antenna-like outer shell at 465 nm for red 2020, and alloyed indium phosphide systems. It also describes stable quantum dot inks with titanium dioxide scattering particles to improve optical density at lower layer thicknesses, plus the giant-shell approach for lifetime.
About the speakers:
* Speakers: Manuel Gensler, Bernd Richter, Lutz Deriks
* Companies: Fraunhofer IAP, IPMS, ILT
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#GiantShellCadmium, #IndiumPhosphideAlloying, #TitaniumDioxideScattering, #BlueAbsorbance465nm, #QuantumDotDisplays, #MicroLEDColorConversion
07:15 - 08:46
How does electrohydrodynamic (EHD) jet printing bypass the physical resolution limits of conventional inkjet printing for microLED displays?
How does electrohydrodynamic (EHD) jet printing bypass the physical resolution limits of conventional inkjet printing for microLED displays?
Conventional inkjet printing is not feasible for the small feature sizes needed in microLED displays. Electrohydrodynamic jet printing instead uses electric fields to print the ink, which reacts to the field and prints from the tip apex of a Taylor cone. This decouples the printing size from the nozzle opening; because of the electric field, even femtoliter droplets reach the surface as directed droplets rather than spraying everywhere over the substrate.
A demo comparing drop-on-print inkjet and EHD jet with pixels and droplets between five and 10 micrometers shows the superior performance of EHD for high-resolution printing. For practical use, the standard single-nozzle printer is the Japan-based Super Inkjet using EHD. The first multi-nozzle systems are available from nJet and from Scrollan in combination with Notion, showing engineering progress for high-resolution printing.
Fraunhofer IAP focuses on material development and ink formulation for EHD jet printing. One new challenge that is not present in inkjet is that there are additional parameters to take care of. The standard single-nozzle printer and emerging multi-nozzle systems are helping push EHD printing toward high-resolution production.
In this short video, you can learn:
* Electrohydrodynamic jet printing decouples printed feature size from nozzle opening by printing from the tip apex of a Taylor cone.
* Even femtoliter droplets reach the surface as directed droplets under the electric field instead of spraying over the substrate.
* The standard single-nozzle EHD printer is the Japan-based Super Inkjet, with first multi-nozzle systems from nJet and Scrollan in combination with Notion.
📋 **Clip Abstract** Electrohydrodynamic jet printing uses electric fields and a Taylor cone to overcome conventional inkjet resolution limits, with droplets between five and 10 micrometers shown in a demo. Fraunhofer IAP focuses on EHD material development and ink formulation as standard single-nozzle and emerging multi-nozzle tools advance high-resolution printing.
About the speakers:
* Speakers: Manuel Gensler, Bernd Richter, Lutz Deriks
* Companies: Fraunhofer IAP, IPMS, ILT
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#EHDJetPrinting, #TaylorConeApex, #FemtoliterDroplets, #SuperInkjet, #MicroLEDDisplays, #PrintedElectronics