We report in this communication the design and fabrication of solutionprocessed white light-emitting diodes (LEDs) containing a bilayer of heavy metal-free colloidal quantum dots (QDs) and polymer in the device active region. White electroluminescence was obtained in the LEDs by mixing the red emission of ZnCuInS/ZnS core/shell QDs and the blue-green emission of poly(N,N 0 -bis(4-butylphenyl)-N,N 0bis(phenyl)benzidine). A high color rendering index of 92 was achieved as compared to a 5310 K blackbody reference by virtue of broadband emission of the QDs. The Commission Internationale de l'Eclairage chromaticity coordinates of the white LED output exhibit a distinctive bias dependence. Finally, aging of the white LEDs was studied, revealing the difference between the photochemical stabilities of the QDs and polymer molecules and the consequent effect on the color evolution of the LEDs.

A Si-based quantum-dot light-emitting diodeWe report the demonstration of mechanically flexible quantum dot light emitting diodes ͑QD-LEDs͒ of all three primary colors ͑red, green, and blue͒. The QD-LEDs have been fabricated over poly͑ethylene-terephthalate͒ substrates and exhibited high brightness, saturated colors, and pronounced flexibility with a critical bending radius of ϳ5 mm. The efficiencies of the flexible QD-LEDs are comparable with the devices fabricated on rigid substrates, suggesting the intrinsic flexibility of quantum dot-based optoelectronic devices.

In this experiment a technique of mist deposition was explored as a way to form patterned ultra-thin-films of CdSe/ZnS core/shell nanocrystalline quantum dots using colloidal solutions. The objective of this study was to investigate the feasibility of mist deposition as a patterning method for creating multicolour quantum dot light emitting diodes. Mist deposition was used to create three rows of quantum dot light emitting diodes on a single device with each row having a separate colour. The colours chosen were red, green and yellow with corresponding peak wavelengths of 620 nm, 558 nm, and 587 nm. The results obtained from this experiment show that it is possible to create multicolour devices on a single substrate. The peak brightnesses obtained in this experiment for the red, green, and yellow were 508 cd/m, 507 cd/m, and 665 cd/m, respectively. The similar LED brightness is important in display technologies using colloidal quantum dots in a precursor solution to ensure one colour does not dominate the emitted spectrum. Results obtained in-terms of brightness were superior to those achieved with inkjet deposition. This study has shown that mist deposition is a viable method for patterned deposition applied to quantum dot light emitting diode display technologies.

This study explores patterned deposition of cadmium selenide (CdSe) nanocrystalline quantum dot (NQD) thin films on paper substrates using the process of mist deposition. Because NQDs film can be engineered to produce unique emissive response, an application that prompted this research is concerned with printing of security/anti-counterfeiting patterns and identification labels on various substrates, including paper. Among other thin-film techniques using colloidal solution as a precursor, mist deposition is in this study predicted through Monte Carlo simulation and demonstrated through experiments to be particularly suitable for creating NQD micro-patterns on paper. In this experiment, barcode-like patterned NQD films were successfully deposited on various types of paper substrates. The films were characterized for fluorescence intensity, emission spectrum and quality of pattern transfer from shadow mask to the deposited film. Time dependent degradation of the deposited pattern was among key aspects investigated. The results obtained indicate that NQD films deposited on paper and encapsulated using plastic laminate did not show degradation in photoluminescence intensity over a period of nine weeks.

This study is concerned with the fabrication of multi-color Light-Emitting Diodes (LEDs) using colloidal solutions of CdSe Nanocrystalline Quantum Dots (NQDs) by the process of mist deposition. CdSe/ZnS core/shell NQDs with red (620 nm), yellow (587 nm) and green (558nm) emissions were deposited to form a patterned tri-color array of quantum dot LEDs. Results obtained from simulation studies show the correlation between the drop size of mist deposition process and the thickness of the resulting NQD films as well as extent of area coverage with mist deposited quantum dots.