Seth Coe-Sullivan

Contact Printing of Quantum Dot Light-Emitting Devices

We demonstrate a solvent-free contact printing process for deposition of patterned and unpatterned colloidal quantum dot (QD) thin films as the electroluminescent layers within hybrid organic-QD light-emitting devices (QD-LEDs). Our method benefits from the simplicity, low cost, and high throughput of solution-processing methods, while eliminating exposure of device structures to solvents. Because the charge transport layers in hybrid organic/inorganic QD-LEDs consist of solvent-sensitive organic thin films, the ability to avoid solvent exposure during device growth, as presented in this study, provides a new flexibility in choosing organic materials for improved device performance. In addition, our method allows us to fabricate both monochrome and red-green-blue patterned electroluminescent structures with 25 microm critical dimension, corresponding to 1000 ppi (pixels-per-inch) print resolution.

A Wafer‐Level Integrated White‐Light‐Emitting Diode Incorporating Colloidal Quantum Dots as a Nanocomposite Luminescent Material

High-brightness, color-tunable colloidal quantum dots are incorporated in 3D nanoporous GaN to create a nanocomposite material (CQD/NP-GaN), which is demonstrated to be an effective approach for a wavelength down-conversion nanomaterial in solid-state lighting. The white-light-emitting diode (LED) made from a blue GaN-based LED and the CQD/NP-GaN shows an increase of extraction efficiency by a factor of 2, a controllable white color, and a down-conversion quantum efficiency as high as 82%.

Highly efficient, spatially coherent distributed feedback lasers from dense colloidal quantum dot films

Colloidal quantum dots (CQD) are now making their entry to full-color displays, endowed by their brightness and single-material base. By contrast, many obstacles have been encountered in their use towards lasers. We demonstrate here optically pumped distributed feedback (DFB) lasers, based on close-packed, solid films self-assembled from type-I CQDs. Notably, the single mode CQD-DFB lasers could reach such a low threshold as to be pumpable with a compact pulsed source in a quasi-continuous wave regime. Our results show the spatially and temporally coherent laser beam outputs with power of 400 μW and a quantum efficiency of 32%.

Surface-emitting red, green, and blue colloidal quantum dot distributed feedback lasers

We demonstrate surface emitting distributed feedback (DFB) lasers across the red, green, and blue from densely packed colloidal quantum dot (CQD) films. The solid CQD films were deposited on periodic grating patterns to enable 2nd-order DFB lasing action at mere 120, 280, and 330 μJ/cm2 of optical pumping energy densities for red, green, and blue DFB lasers, respectively. The lasers operated in single mode operation with less than 1 nm of full-width-half-maximum. We measured far-field patterns showing high degree of spatial beam coherence. Specifically, by taking advantage of single exciton optical gain regime from our engineered CQDs, we can significantly suppress the Auger recombination to reduce lasing threshold and achieve quasi-steady state, optically pumped operation.

High-resolution photocurrent microscopy using near-field cathodoluminescence of quantum dots

We report a fast, versatile photocurrent imaging technique to visualize the local photo response of solar energy devices and optoelectronics using near-field cathodoluminescence (CL) from a homogeneous quantum dot layer. This approach is quantitatively compared with direct measurements of high-resolution Electron Beam Induced Current (EBIC) using a thin film solar cell (n-CdS / p-CdTe). Qualitatively, the observed image contrast is similar, showing strong enhancement of the carrier collection efficiency at the p-n junction and near the grain boundaries. The spatial resolution of the new technique, termed Q-EBIC (EBIC using quantum dots), is determined by the absorption depth of photons. The results demonstrate a new method for high-resolution, sub-wavelength photocurrent imaging measurement relevant for a wide range of applications.

12.2: Invited Paper: Quantum Dot Light Emitting Diodes for Near-to-eye and Direct View Display Applications

Quantum dot light emitting diodes QLEDs are a printable thin film electroluminescent technology that can deliver exceptional color and efficiency at low cost of manufacture for display and solid-state lighting applications. However, while most literature reports focus on the performance of individual test pixels, examples of working display prototypes have been sorely lacking. We report on our progress developing QLEDs for near-to-eye and direct view display applications. Both a 4″ diagonal active-matrix bottom-emitting monochrome QLED display and an 800×600 SVGA top-emitting monochrome QLED microdisplay are reported on and their performance summarized. Contract printing of high-resolution RGB QDs is also demonstrated as a milestone towards full-color displays.

P-176: Progress in Developing High Efficiency Quantum Dot Displays

LED displays utilizing quantum dots (QDs) as emitters offer several key advantages over traditional OLEDs, combining the solution processability of polymers with the high efficiency potential of phosphors, all with the stability benefits of an inorganic emitter. While QD-LEDs are at an early stage in their development, the effort toward commercialization has already led to the identification of several considerations particular to QD-LEDs. This paper explores material and design considerations for QD-LEDs and reports our progress in developing QD-LEDs for information display and advanced applications.

Method for fabrication of saturated RGB quantum dot light emitting devices

Creation of patterned, efficient, and saturated color hybrid organic/inorganic quantum dot light emitting devices (QD-LEDs) is dependent on development of integrated fabrication and patterning methods for the QD layer. We show that micro-contact printing can be applied to QD deposition, generating micron-scale pattern definition, needed in pixilated-display applications. We demonstrate saturated color QD-LEDs with external quantum efficiencies in excess of 1%. Combining this technique with the use of wide optical band gap host materials, and a new synthetic route for the creation of blue emitting (CdS)ZnS nanocrystals, it is now possible to fabricate QD-LEDs with saturated color emission in the red, green and blue regions of the spectrum.

32.4: Quantum Dot Light Emitting Diodes for Full‐color Active‐matrix Displays

Quantum dot light emitting diodes (QLEDs) are a printable thin film electroluminescent technology that delivers exceptional color and efficiency at low cost of manufacture for display and solid- state lighting applications. We report on our progress developing efficient, stable QLEDs for full-color active-matrix displays, including recent advances in device performance, lifetime and Cadmium-free QLEDs. Current QLED devices exhibit peak luminance efficiencies exceeding 50 cd/A, luminous power efficiencies greater than 20 lm/W and operational lifetimes exceeding 300 hours at 1,000 nits. Our most recent QLED efficiency results suggest that todays QLED performance is within a factor of two of the theoretical limit.

Transient gain spectroscopy in the potent single-exciton regime of dense II-VI colloidal quantum dot films

We have reached the long-sought single exciton gain regime in dense colloidal II-VI semiconductor quantum dot films. Transient spectroscopy details their exciton dynamics, informing further development of single material based lasers across the visible.