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Wolfgang Heiss

Bio: Wolfgang Heiss is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Quantum dot & Photoluminescence. The author has an hindex of 46, co-authored 220 publications receiving 9361 citations. Previous affiliations of Wolfgang Heiss include Johannes Kepler University of Linz & Lawrence Berkeley National Laboratory.


Papers
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Journal ArticleDOI
TL;DR: Low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 are reported.
Abstract: Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440–700 nm) with low pump thresholds down to 5±1 μJ cm−2 and high values of modal net gain of at least 450±30 cm−1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals. Lead halide perovskite colloidal nanocrystals have promising optoelectronic properties, such as high photoluminescence quantum yields and narrow emission linewidths. Here, the authors report low-threshold amplified spontaneous emission and two kinds of lasing in nanostructured caesium lead halide perovskites.

1,305 citations

Journal ArticleDOI
22 Jan 2015-ACS Nano
TL;DR: The state of the art in research on colloidal NCs is reviewed focusing on the most recent works published in the last 2 years, where semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available.
Abstract: Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenom...

988 citations

Journal ArticleDOI
TL;DR: Here it is demonstrated a possibility to use such inexpensive semiconductors for sensitive detection of X-ray photons by direct photon-to-current conversion and a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms.
Abstract: The evolution of real-time medical diagnostic tools such as angiography and computer tomography from radiography based on photographic plates was enabled by the development of integrated solid-state X-ray photon detectors, based on conventional solid-state semiconductors. Recently, for optoelectronic devices operating in the visible and near infrared spectral regions, solution-processed organic and inorganic semiconductors have also attracted immense attention. Here we demonstrate a possibility to use such inexpensive semiconductors for sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH3NH3PbI3) offers a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms. Solution processed photodiodes as well as photoconductors are presented, exhibiting high values of X-ray sensitivity (up to 25 µC mGyair-1 cm-3) and responsivity (1.9×104 carriers/photon), which are commensurate with those obtained by the current solid-state technology.

830 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported the fabrication and application of hybrid bulk heterojunction photodiodes containing PbS nanocrystalline quantum dots as sensitizers for near-infrared detection up to 1.8 µm.
Abstract: Solution-processed photodiodes with infrared sensitivities at wavelengths beyond the bandgap of silicon (corresponding to a wavelength of ∼1,100 nm) would be a significant advance towards cost-effective imaging. Colloidal quantum dots are highly suitable as infrared absorbers for photodetection, but high quantum yields have only been reported with photoconductors1,2,3. For imaging, photodiodes are required to ensure low-power operation and compatibility to active matrix backplanes4. Organic bulk heterojunctions5 are attractive as solution-processable diodes, but are limited to use in the visible spectrum. Here, we report the fabrication and application of hybrid bulk heterojunction photodiodes containing PbS nanocrystalline quantum dots as sensitizers for near-infrared detection up to 1.8 µm, with rectification ratios of ∼6,000, minimum lifetimes of one year and external quantum efficiencies of up to 51%. By integration of the solution-processed devices on amorphous silicon active matrix backplanes, we demonstrate for the first time near-infrared imaging with organic/inorganic hybrid photodiodes. Near-infrared imaging with solution-processed organic–inorganic hybrid photodiodes is demonstrated for the first time. The hybrid bulk-heterojunction photodiodes contain PbS nanocrystalline quantum dots as sensitizers for the detection of light of up to 1.8 µm in wavelength, have a minimum lifetime of one year, and external quantum efficiencies of up to 51%.

597 citations

Journal ArticleDOI
TL;DR: Various oleic acid salts are demonstrated to act as stabilizers for high-quality iron oxide nanocrystals, synthesized by thermal decomposition of ferric oleate, with different degrees of dissociation at high temperatures to be obtained.
Abstract: Various oleic acid salts are demonstrated to act as stabilizers for high-quality iron oxide nanocrystals, synthesized by thermal decomposition of ferric oleate. Changing the cation species in oleic acid salts allows different degrees of dissociation at high temperatures to be obtained, resulting in various stabilizer performances: Sodium oleate as stabilizer results in monodisperse iron oxide nanocrystals of cubic shape with precisely adjustable edge lengths between 7 and 23 nm. Dibutylammonium oleate and oleic acid, in contrast, induce growth of spherical nanocrystals in the same size range. Further adjustment of the growth conditions leads to {100}-bound bipyramidal nanocrystals with a single, (111) oriented twin plane. While the nanocrystal size is related to their superparamagnetic blocking temperature, the shape influences their magnetization hysteresis properties observed at low temperatures.

368 citations


Cited by
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Journal ArticleDOI
10 Mar 1970

8,159 citations

Journal ArticleDOI
TL;DR: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each that are among the hottest research topics of the last decades.
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

3,720 citations

Journal ArticleDOI
TL;DR: In this paper, the triple cation perovskite photovoltaics with inorganic cesium were shown to be thermally more stable, contain less phase impurities and are less sensitive to processing conditions.
Abstract: Today's best perovskite solar cells use a mixture of formamidinium and methylammonium as the monovalent cations. With the addition of inorganic cesium, the resulting triple cation perovskite compositions are thermally more stable, contain less phase impurities and are less sensitive to processing conditions. This enables more reproducible device performances to reach a stabilized power output of 21.1% and ∼18% after 250 hours under operational conditions. These properties are key for the industrialization of perovskite photovoltaics.

3,470 citations

Journal ArticleDOI
TL;DR: An overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of differentTwo-dimensional crystals or of two- dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides are provided.
Abstract: Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides

3,025 citations

Journal ArticleDOI
TL;DR: This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties ofatomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles.
Abstract: Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

2,144 citations