Hybrid organic/quantum dot thin film structures and devices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 157-169).Organic light emitting diodes have undergone rapid advancement over the course of the past decade. Similarly, quantum dot synthesis has progressed to the point that room temperature highly efficient photoluminescence can be realized. It is the purpose of this work to utilize the beneficial properties of these two material sets in a robust light emitting device. New deposition techniques are necessary to the realization of this goal, enabling QD organic hybrids to be created in a quick and reliable manner compatible with known device fabrication methods. With these techniques, quantum dot light emitting devices are fabricated, measured, and analyzed. The devices are of high efficiency and color saturation, and provide us with a test bed for understanding the interactions between inorganic QDs and organic thin films.by Seth Coe-Sullivan.Ph.D

Submicron full- color LED pixels for microdisplays and micro- LED main displays

We demonstrate a bottom- up approach to the construction of micro- LEDs as small as 150 nm in lateral dimension. Molecular beam epitaxy (MBE) is used to fabricate such nanostructured LEDs from InGaN, from the blue to red regions of the spectrum, providing a single material set useful for an entire RGB display.We demonstrate a bottom- up approach to the construction of micro- LEDs as small as 150 nm in lateral dimension. Molecular beam epitaxy (MBE) is used to fabricate such nanostructured LEDs from InGaN, from the blue to red regions of the spectrum, providing a single material set useful for an entire RGB display. We then consider collective effects of arrays of such LEDs.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155468/1/jsid899_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155468/2/jsid899.pd

Efficient LEDs utilizing CdSe(ZnS) quantum dots in organic host matrices

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 29-32).We demonstrate efficient electroluminescence from thin film structures containing core-shell CdSe(ZnS) quantum dots dispersed in molecular organic host materials. In the most efficient devices, excitons are created on the quantum dot sites via energy transfer from organic host molecules, and direct charge injection into the quantum dots is minimized. For quantum dots with core diameter 38 [Angstroms], the electroluminescence spectra peak at 562nm and have full width at half maximum as narrow as 32nm. Saturated color devices have external quantum efficiencies as high as 0.61% at the current density of 7mA/cm². At 125mA/cm², the device luminance is 1900cd/m², which corresponds to a luminescence efficiency of 1.5 cd/A. The yield over hundreds of devices is greater than 90%, indicating a robust material system.by Seth Alexander Coe.S.M

Quantum Dot Light Enhancement Substrate for OLED Solid-State Lighting

With DOE Award No. DE-EE00000628, QD Vision developed and demonstrated a cost-competitive solution for increasing the light extraction efficiency of OLEDs with efficient and stable color rendering index (CRI) for solid state lighting (SSL). Solution processable quantum dot (QD) films were integrated into OLED ITO-glass substrates to generate tunable white emission from blue emitting OLED) devices as well as outcouple light from the ITO film. This QD light-enhancement substrate (QD-LED) technology demonstrated a 60% increase in OLED forward light out-coupling, a value which increases to 76% when considering total increase in multi-directional light output. The objective for the first year was an 80% increase in light output. This project seeks to develop and demonstrate a cost-competitive solution for realizing increased extraction efficiency organic light emitting devices (OLEDs) with efficient and stable color rendering index (CRI) for SSL. Solution processible quantum dot (QD) films will be utilized to generate tunable white emission from blue emitting phosphorescent OLED (Ph-OLED) devices

Quantum Dot Light Enhancement Substrate for OLED Solid-State Lighting

With DOE Award No. DE-EE00000628, QD Vision developed and demonstrated a cost-competitive solution for increasing the light extraction efficiency of OLEDs with efficient and stable color rendering index (CRI) for solid state lighting (SSL). Solution processable quantum dot (QD) films were integrated into OLED ITO-glass substrates to generate tunable white emission from blue emitting OLED) devices as well as outcouple light from the ITO film. This QD light-enhancement substrate (QD-LED) technology demonstrated a 60% increase in OLED forward light out-coupling, a value which increases to 76% when considering total increase in multi-directional light output. The objective for the first year was an 80% increase in light output. This project seeks to develop and demonstrate a cost-competitive solution for realizing increased extraction efficiency organic light emitting devices (OLEDs) with efficient and stable color rendering index (CRI) for SSL. Solution processible quantum dot (QD) films will be utilized to generate tunable white emission from blue emitting phosphorescent OLED (Ph-OLED) devices

30‐3: Distinguished Paper: Sub‐Micron Full‐Color LED Pixels for Micro‐Displays and Micro‐LED Main Displays

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162729/2/sdtp13897_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162729/1/sdtp13897.pd

Red, green and blue lasing enabled by single-exciton gain in colloidal quantum dot films

Colloidal quantum dots exhibit efficient photoluminescence with widely tunable bandgaps as a result of quantum confinement effects1. Such quantum dots are emerging as an appealing complement to epitaxial semiconductor laser materials, which are ubiquitous and technologically mature, but unable to cover the full visible spectrum (red, green and blue; RGB)2. However, the requirement for high colloidal-quantum-dot packing density, and losses due to non-radiative multiexcitonic Auger recombination, have hindered the development of lasers based on colloidal quantum dots3, 4, 5, 6, 7, 8, 9. Here, we engineer CdSe/ZnCdS core/shell colloidal quantum dots with aromatic ligands, which form densely packed films exhibiting optical gain across the visible spectrum with less than one exciton per colloidal quantum dot on average. This single-exciton gain allows the films to reach the threshold of amplified spontaneous emission at very low optical pump energy densities of 90 µJ cm–2, more than one order of magnitude better than previously reported values9, 10, 11, 12. We leverage the low-threshold gain of these nanocomposite films to produce the first colloidal-quantum-dot vertical-cavity surface-emitting lasers (CQD-VCSEL). Our results represent a significant step towards full-colour single-material lasers.Accepted versio

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.Published versio