An official website of the United States government
Both organohalide perovskites and colloidal quantum dots are attractive and promising materials for optoelectronic applications. Recent experiments have combined the two to create “quantum dot-in-perovskite” assemblies for highly efficient light emissions. In this work, we unravel photoexcitation dynamics at the interface between the perovskite and the quantum dot by means of first-principle non-adiabatic molecular dynamics simulations. We find that such assemblies adopt the type-I band structure and are free of defect states. The interfacial and the electronic structure are robust against the thermal fluctuations at 300K. The lowest excitation is predicted to be localized entirely on the quantum dot and the photoexcited charge transfer takes place in a picosecond timescale. The charge transfer dynamics of the photoexcited electron and hole exhibits a moderate asymmetry, which can be attributed to the differences in electronic coupling between the donor and the acceptor and the electron-phonon coupling. The ultrafast and balanced charge transfer dynamics endows the ‘dot-in-a-crystal’ devices with unprecedented performance, which could lead to important applications in photovoltaics, photocatalysis, and infrared light emissions.
more »
« less
Composite Structures with Emissive Quantum Dots for Light Enhancement
Abstract Since their inception, quantum dots have proven to be advantageous for light management applications due to their high brightness and well‐controlled absorption, scattering, and emission properties. As quantum dots become commercially available at large scale, the need for robust, stable, and flexible optical components continues to drive the development of robust and flexible quantum dot composite materials. In this review, after a thorough introduction to quantum dots, discussion delves into methods for fabricating quantum dot loaded composite optical elements such as thin films, microfabricated patterns, and microstructures. The importance of surface chemistry and ligand engineering, host matrixes, wet processing, and unique patterning methodologies is presented by considering photostability, aggregation, and phase separation of quantum dots in corresponding composites. With regard to prospective optical applications of quantum dot materials, emphasis is placed on light emitting and guiding composite materials for lasing applications, specifically whispering gallery mode‐based photonic microsystems. These developments will enable novel flexible, portable, and miniaturized optoelectronic devices such as light‐emitting diodes, flexible pixelated displays, solar cells, large‐area microwaveguides, omnidirectional micromirrors, optical metasurfaces, and directional microlasers.
more »
« less
- Award ID(s):
- 1803495
- PAR ID:
- 10462470
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 7
- Issue:
- 4
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Widespread clinical adoption of photodynamic therapy (PDT) and photobiomodulation (PBM) has been limited due to the lack of a suitable commercial light source. Cost-effective quantum dot light-emitting diodes (QLEDs) promise to be an ideal light source nicely fitting into this niche, not only complying with desired form factors—flexibility, lightweight, and uniform large area illumination—but with narrow emission spectrum and high power density at clinically relevant deep red wavelengths. This paper is intended to provide a review on the development of QLEDs as a photomedical light source, specifically, for PDT and PBM. First, we introduce the potential of QLEDs as light sources in the photomedical field, briefly describe the mechanisms and benefits of both PDT and PBM phototherapies, and present the unique features of flexible QLEDs (FQLEDs) over conventional and commercial light sources. Then, the pioneering work and state-of-the-art research using QLEDs and organic light emitting diodes (OLEDs) for photomedicine are presented. The performance of QLEDs/OLEDs used in photomedical studies and latest progress on QLEDs are also summarized. Ultimately, we discuss the materials and design strategies for fabrication of efficient and stable FQLEDs, and present the basic requirements for near future introduction of FQLEDs into the healthcare and photomedicine markets. This review is expected to be comprehensive and useful to the scientific community interested in developing lightweight and flexible light sources for photomedicine and/or exploring novel applications for OLED/QLED based lighting devices.more » « less
-
Optically pumped white light-emitting diodes (WLEDs), consisting of blue/ultraviolet LED chips and down conversion phosphors, have a wide range of applications in our daily life, such as full color display and solid-state lighting. While remarkable progress in light quality, device efficiency, and lifetime has been achieved during the last two decades, many challenges remain in optically pumped WLEDs, and searching for low cost high performance down conversion phosphors is still of great interest. Recently, metal halide perovskites have emerged as a highly promising new generation of light emitters for their exceptional optical properties with high quantum efficiencies and color tunability, which have also inspired researchers to investigate their derivatives. In this perspective, we briefly review the progress during the last few years in the development of metal halide perovskites and perovskite-related materials as down conversion phosphors for optically pumped WLEDs. We also highlight some major issues and challenges that need to be addressed to enable perovskite-based light emitters to possibly replace currently used rare-earth doped inorganic phosphors and quantum dots.more » « less
-
Both absorption and emission of light in semiconductor quantum dots occur through excitation or recombination of confined electron−hole pairs, or excitons, with tunable size-dependent resonant frequencies that are ideal for applications in various fields. Some of these applications require control over quantum dot shape uniformity, while for others, control over energy splittings among exciton states emitting light in different polarizations and/or between bright and dark exciton states is of key importance. These splittings, known as exciton fine structure, are very sensitive to the nanocrystal shape. Theoretically, nanocrystals of spheroidal shape are often considered, and their nonsphericity is treated perturbatively as stemming from a linear uniaxial deformation of a sphere. Here, we compare this treatment with a nonperturbative model of a cylindrical box, free of any restrictions on the cylinder’s aspect ratio. This comparison allows one to understand the limits of validity of the traditional perturbative model and offers insights into the relative importance of various mechanisms controlling the exciton fine structure. These insights are relevant to both colloidal nanocrystals and epitaxial quantum dots of III−V and II−VI semiconductors.more » « less
-
Light emitting diodes (LEDs) have wide applications from fullcolor displays to solid‐state lighting. Numerous types of luminescent materials have been explored for LEDs, ranging from inorganic semiconductors to metal complexes and quantum dots. Despite the rapid pace of development, LEDs have not achieved their full potentials in terms of performance and cost efficiency. Identifying new eco‐friendly materials for LEDs is of great interest. Recently, metal halide perovskites and perovskite‐related hybrid materials have emerged as new generation luminescent materials with unique optoelectronic properties. Here, some of our recent development of LEDs based on metal halide perovskites and perovskite‐related materials will be discussed.more » « less
