October 13, 2011 — Researchers from the Samsung Advanced Institute of Technology (SAIT) and the University of Cambridge created a full-color high-resolution 4" quantum dot light emitting diode (QD-LED) display using transfer printing (Nature Photonics, 2011).

Figure. Transfer printing for patterning quantum dots (QDs). (i) Modification of the donor surface with SAM, and spin-coating of QDs. (ii) Application of an elastomer stamp to the QD film with appropriate pressure. (iii) Peeling of the stamp, quickly, from the donor substrate. (iv) Contacting the inked stamp to the device stack, and slowly peeling back the stamp. (v)–(vii) Sequential transfer printing of green and blue QDs. b, Fluorescence micrograph of the transfer-printed RGB QD stripes onto the glass substrate, excited by 365 nm UV radiation.

The team began by modifying the donor substrate surface with a chemically bound self-assembled monolayer (SAM). Red-, green-, and blue-emissive quantum dots are printed via the same precise process at room temperature. Various substrates could be used, including flexible ITO/PEN. Future work will focus on scaling the printing process to industrial production without degrading resolution. Aligning the different color QD stripes over large-area may pose a challenge, notes Khashayar Ghaffarzadeh, technology analyst, IDTechEx.
 
QD-LEDs are electroluminescent colloidal quantum dots that can be printed in thin films to combine inorganic LEDs’ customizable, saturated, stable color and low-voltage performance with polymers’ solution processability, said Ghaffarzadeh.

Also read: Quantum dot OLEDs fabbed via spin coating

For QD-LEDs to work, the thin film transistors (TFTs) in the active-matrix backplane must supply a very stable current. New backplane technologies like metal oxides could replace amorphous silicon for this function. Researchers from the University of Cambridge have also demonstrated solution-processed high-performance metal-oxide TFTs (Nature Materials, 2011) with a <250°C annealing temperature.

The University of Cambridge will present at IDTechEx’s Printed Electronics USA. Printed Electronics USA 2011 will take place November 29-December 2 in Santa Clara, CA, with tours to local centers of excellence. Learn more at www.IDTechEx.com/peUSA.

References:
Full-colour quantum dot displays fabricated by transfer printing, Nature Photonics 5, 176-182, (2011). Low-temperature, high-performance solution-processed metal oxide thin-film transistors formed by a ‘sol-gel on chip’ process, Nature Materials 10, 45-50(2011).

IDTechEx provides custom consulting, research and advisory services in Printed Electronics, RFID, Photovoltaics, Energy Harvesting and Electric Vehicles. Learn more at www.IDTechEx.com/nano.