Ting Zhu

Bio: Ting Zhu is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Quantum dot & Nanocrystal. The author has an hindex of 15, co-authored 29 publications receiving 1991 citations. Previous affiliations of Ting Zhu include Foundation University, Islamabad.

Bright, multicoloured light-emitting diodes based on quantum dots

Abstract: Quantum-dot-based LEDs are characterized by pure and saturated emission colours with narrow bandwidth, and their emission wavelength is easily tuned by changing the size of the quantum dots. However, the brightness, efficiency and lifetime of LEDs need to be improved to meet the requirements of commercialization in the near future. Here, we report red, orange, yellow and green LEDs with maximum luminance values of 9,064, 3,200, 4,470 and 3,700 cd m−2, respectively, the highest values reported so far. Solution-processable core–shell quantum dots with a CdSe core and a ZnS or CdS/ZnS shell were used as emissive layers in the devices. By optimizing the thicknesses of the constituent layers of the devices, we were able to develop quantum-dot-based LEDs with improved electroluminescent efficiency (1.1–2.8 cd A−1), low turn-on voltages (3–4 V) and long operation lifetimes. These findings suggest that such quantum-dot-based LEDs will be promising for use in flat-panel displays.

Harvest of near infrared light in PbSe nanocrystal-polymer hybrid photovoltaic cells

Abstract: We report a hybrid photovoltaic cell where PbSe nanocrystals were used to sensitize the conjugated polymer into the infrared. The device exhibited an incident monochromatic photon to current conversion efficiency of 1.3% at λ=805nm. Under 1 sun AM 1.5 illumination, the infrared response (780nm<λ<1600nm) of the embedded nanocrystals contributes to 33% of the overall photocurrent of the photovoltaic cell. The observed intensity dependences of the photocurrents have revealed the pseudomonomolecular recombination kinetics in the nanocrystal quantum dot polymer composite, indicating that the efficiency of the hybrid photovoltaic cells can be enhanced by reducing the potential barriers due to the ligand molecules at the surfaces of nanocrystals.

Bright and color-saturated emission from blue light-emitting diodes based on solution-processed colloidal nanocrystal quantum dots

Abstract: We report a multilayer solution-processed blue light-emitting diode based on colloidal core/shell CdS/ZnS nanocrystal quantum dots (QDs). At a low-operating voltage of 5.5 V, the device emits spectrally pure blue radiation at 460 nm with a narrow full-width-at-half-maximum bandwidth of 20 nm and high brightness up to 1600 cd/m2. Broad-band, long-wavelength emission from the polymer components and deep traps in the QDs are minimized to less than 5% of the total emission.

Enhanced spontaneous emission at 1.55 μm from colloidal PbSe quantum dots in a Si photonic crystal microcavity

Abstract: The authors report on the design, fabrication, and characterization of 1.55μm Si-based photonic crystal microcavity light emitters utilizing PbSe quantum dots. Efficient coupling of emission from PbSe quantum dots to Si photonic crystal membrane microcavity is achieved by inserting the quantum dots in a central air hole in the microcavity. Enhancement of spontaneous emission with linewidth of ∼2.0nm is observed at 1550nm at room temperature. The Purcell factor and the spontaneous emission coupling factor are estimated to be 35 and 0.04, respectively.

Mist fabrication of light emitting diodes with colloidal nanocrystal quantum dots

Abstract: In this letter, we report a mist-deposition process for the assembly and patterning of nanocrystal quantum dots (NQDs) during the fabrication of quantum dot light emitting diodes (QD-LEDs), which allows for tight controls over the thickness, surface morphology, composition, and resolution of NQD emissive layers. A defect-free featuring uniform brightness QD-LED containing a mist-deposited emissive CdSe(ZnS) NQD layer was demonstrated. Additionally, the technique of successive mist deposition of multicolor NQDs through a set of registered shallow masks was employed to create a 6×6 matrix of alternating pixels composed of 5nm diameter CdSe(ZnS) NQDs (green) and 8nm diameter CdSe(ZnS) NQDs (red) on the same substrate. The results obtained demonstrate the potential of mist-deposition technology in the future development of full-color QD-LED displays.

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Emergence of colloidal quantum-dot light-emitting technologies

Abstract: This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.

Core/Shell semiconductor nanocrystals.

Abstract: Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

Abstract: Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well a...

Semiconductor nanowires for energy conversion.

Abstract: Semiconductor nanowires represent an important class of nanostructure building block for photovoltaics as well as direct solar-to-fuel application because of their high surface area, tunable bandgap and efficient charge transport and collection. In this talk, I will highlight several recent examples in this lab using semiconductor nanowires and their heterostructures for the purpose of solar energy harvesting. In addition, we have also discovered that the thermoconductivity of the silicon nanowires can be significantly reduced due to phonon scattering, pointing to a very promising approach to design better thermoelectrical materials. It is important to note that the engines that generate most of the world's power typically operate at only 30–40 per cent efficiency, releasing roughly 15 terawatts of heat to the environment. If this “wasted heat” could be recycled, the impact globally would be enormous. Our silicon nanowire thermoelectric technology could have a significant impact in alternative energy generation.