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 made from 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 a great deal of attention. Here, we demonstrate a possibility to use such inexpensive semiconductors for the sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH3 NH3 PbI3 ) 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.
The conversion of thermal energy to electricity and vice versa by means of solid state thermoelectric devices is extremely appealing. However, its cost-effectiveness is seriously hampered by the ...relatively high production cost and low efficiency of current thermoelectric materials and devices. To overcome present challenges and enable a successful deployment of thermoelectric systems in their wide application range, materials with significantly improved performance need to be developed. Nanostructuration can help in several ways to reach the very particular group of properties required to achieve high thermoelectric performances. Nanodomains inserted within a crystalline matrix can provide large charge carrier concentrations without strongly influencing their mobility, thus allowing to reach very high electrical conductivities. Nanostructured materials contain numerous grain boundaries that efficiently scatter mid- and long-wavelength phonons thus reducing the thermal conductivity. Furthermore, nanocrystalline domains can enhance the Seebeck coefficient by modifying the density of states and/or providing type- and energy-dependent charge carrier scattering. All these advantages can only be reached when engineering a complex type of material, nanocomposites, with exquisite control over structural and chemical parameters at multiple length scales. Since current conventional nanomaterial production technologies lack such level of control, alternative strategies need to be developed and adjusted to the specifics of the field. A particularly suitable approach to produce nanocomposites with unique level of control over their structural and compositional parameters is their bottom-up engineering from solution-processed nanoparticles. In this work, we review the state-of-the-art of this technology applied to the thermoelectric field, including the synthesis of nanoparticles of suitable materials with precisely engineered composition and surface chemistry, their combination and consolidation into nanostructured materials, the strategies to electronically dope such materials and the attempts to fabricate thermoelectric devices using nanoparticle-based nanopowders and inks.
Colloidal nanocrystals (NCs) of APbX3-type lead halide perovskites A = Cs+, CH3NH3 + (methylammonium or MA+) or CH(NH2)2 + (formamidinium or FA+); X = Cl–, Br–, I– have recently emerged as highly ...versatile photonic sources for applications ranging from simple photoluminescence down-conversion (e.g., for display backlighting) to light-emitting diodes. From the perspective of spectral coverage, a formidable challenge facing the use of these materials is how to obtain stable emissions in the red and infrared spectral regions covered by the iodide-based compositions. So far, red-emissive CsPbI3 NCs have been shown to suffer from a delayed phase transformation into a nonluminescent, wide-band-gap 1D polymorph, and MAPbI3 exhibits very limited chemical durability. In this work, we report a facile colloidal synthesis method for obtaining FAPbI3 and FA-doped CsPbI3 NCs that are uniform in size (10–15 nm) and nearly cubic in shape and exhibit drastically higher robustness than their MA- or Cs-only cousins with similar sizes and morphologies. Detailed structural analysis indicated that the FAPbI3 NCs had a cubic crystal structure, while the FA0.1Cs0.9PbI3 NCs had a 3D orthorhombic structure that was isostructural to the structure of CsPbBr3 NCs. Bright photoluminescence (PL) with high quantum yield (QY > 70%) spanning red (690 nm, FA0.1Cs0.9PbI3 NCs) and near-infrared (near-IR, ca. 780 nm, FAPbI3 NCs) regions was sustained for several months or more in both the colloidal state and in films. The peak PL wavelengths can be fine-tuned by using postsynthetic cation- and anion-exchange reactions. Amplified spontaneous emissions with low thresholds of 28 and 7.5 μJ cm–2 were obtained from the films deposited from FA0.1Cs0.9PbI3 and FAPbI3 NCs, respectively. Furthermore, light-emitting diodes with a high external quantum efficiency of 2.3% were obtained by using FAPbI3 NCs.
The spatial localization of charge carriers to promote the formation of bound excitons and concomitantly enhance radiative recombination has long been a goal for luminescent semiconductors. ...Zero‐dimensional materials structurally impose carrier localization and result in the formation of localized Frenkel excitons. Now the fully inorganic, perovskite‐derived zero‐dimensional SnII material Cs4SnBr6 is presented that exhibits room‐temperature broad‐band photoluminescence centered at 540 nm with a quantum yield (QY) of 15±5 %. A series of analogous compositions following the general formula Cs4−xAxSn(Br1−yIy)6 (A=Rb, K; x≤1, y≤1) can be prepared. The emission of these materials ranges from 500 nm to 620 nm with the possibility to compositionally tune the Stokes shift and the self‐trapped exciton emission bands.
Fully inorganic, perovskite‐derived zero‐dimensional Cs4SnBr6 exhibits room‐temperature broad‐band photoluminescence from self‐trapped excitons, centered at 540 nm with a quantum yield of 15±5 % (298 K; near 100 % at 200 K), and a large Stokes shift of ca.1.2 eV. A compositional series, Cs4−xAxSn(Br1−yIy)6 (A=Rb, K; x≤1, y≤1), was obtained wherein the emission peak ranges from 500 nm to 620 nm.
Many in-memory computing frameworks demand electronic devices with specific switching characteristics to achieve the desired level of computational complexity. Existing memristive devices cannot be ...reconfigured to meet the diverse volatile and non-volatile switching requirements, and hence rely on tailored material designs specific to the targeted application, limiting their universality. "Reconfigurable memristors" that combine both ionic diffusive and drift mechanisms could address these limitations, but they remain elusive. Here we present a reconfigurable halide perovskite nanocrystal memristor that achieves on-demand switching between diffusive/volatile and drift/non-volatile modes by controllable electrochemical reactions. Judicious selection of the perovskite nanocrystals and organic capping ligands enable state-of-the-art endurance performances in both modes - volatile (2 × 10
cycles) and non-volatile (5.6 × 10
cycles). We demonstrate the relevance of such proof-of-concept perovskite devices on a benchmark reservoir network with volatile recurrent and non-volatile readout layers based on 19,900 measurements across 25 dynamically-configured devices.
Lead halide perovskites have emerged as promising new semiconductor materials for high-efficiency photovoltaics, light-emitting applications and quantum optical technologies. Their luminescence ...properties are governed by the formation and radiative recombination of bound electron-hole pairs known as excitons, whose bright or dark character of the ground state remains unknown and debated. While symmetry analysis predicts a singlet non-emissive ground exciton topped with a bright exciton triplet, it has been predicted that the Rashba effect may reverse the bright and dark level ordering. Here, we provide the direct spectroscopic signature of the dark exciton emission in the low-temperature photoluminescence of single formamidinium lead bromide perovskite nanocrystals under magnetic fields. The dark singlet is located several millielectronvolts below the bright triplet, in fair agreement with an estimation of the long-range electron-hole exchange interaction. Nevertheless, these perovskites display an intense luminescence because of an extremely reduced bright-to-dark phonon-assisted relaxation.
The decay of the majority of radioactive isotopes involves the emission of gamma ( gamma ) photons with energies of 50keV to 10MeV. Detectors of such hard radiation that are low-cost, highly ...sensitive and operate at ambient temperatures are desired for numerous applications in defence and medicine, as well as in research. We demonstrate that 0.3-1cm solution-grown single crystals (SCs) of semiconducting hybrid lead halide perovskites (MAPbI sub(3), FAPbI sub(3) and I-treated MAPbBr sub(3), where MA=methylammonium and FA=formamidinium) can serve as solid-state gamma-detecting materials. This possibility arises from a high charge-carrier mobility-lifetime ( mu tau ) product of 1.0-1.810 super(-2)cm super(2)V super(-1), a low dark carrier density of 10 super(9)-10 super(11)cm super(-3) (refs 3,4), a low density of charge traps of 10 super(9)-10 super(10)cm super(-3) (refs 4,5) and a high absorptivity of hard radiation by the lead and iodine atoms. We demonstrate the utility of perovskite detectors for testing the radiopurity of medical radiotracer compounds such as super(18)F-fallypride. Energy-resolved sensing at room temperature is presented using FAPbI sub(3) SCs and an super(241)Am source.
Flexible, thin-film electronic and optoelectronic devices typically involve a trade-off between performance and fabrication cost. For example, solution-based deposition allows semiconductors to be ...patterned onto large-area substrates to make solar cells and displays, but the electron mobility in solution-deposited semiconductor layers is much lower than in semiconductors grown at high temperatures from the gas phase. Here, we report band-like electron transport in arrays of colloidal cadmium selenide nanocrystals capped with the molecular metal chalcogenide complex In(2)Se(4)(2-), and measure electron mobilities as high as 16 cm(2) V(-1) s(-1), which is about an order of magnitude higher than in the best solution-processed organic and nanocrystal devices so far. We also use CdSe/CdS core-shell nanoparticles with In(2)Se(4)(2-) ligands to build photodetectors with normalized detectivity D* > 1 × 10(13) Jones (I Jones = 1 cm Hz(1/2) W(-1)), which is a record for II-VI nanocrystals. Our approach does not require high processing temperatures, and can be extended to different nanocrystals and inorganic surface ligands.
Replacement of Li-ion liquid-state electrolytes by solid-state counterparts in a Li-ion battery (LIB) is a major research objective as well as an urgent priority for the industry, as it enables the ...use of a Li metal anode and provides new opportunities to realize safe, non-flammable, and temperature-resilient batteries. Among the plethora of solid-state electrolytes (SSEs) investigated, garnet-type Li-ion electrolytes based on cubic Li
La
Zr
O
(LLZO) are considered the most appealing candidates for the development of future solid-state batteries because of their low electronic conductivity of ca. 10
S cm
(RT) and a wide electrochemical operation window of 0-6 V vs. Li
/Li. However, high LLZO density (5.1 g cm
) and its lower level of Li-ion conductivity (up to 1 mS cm
at RT) compared to liquid electrolytes (1.28 g cm
; ca. 10 mS cm
at RT) still raise the question as to the feasibility of using solely LLZO as an electrolyte for achieving competitive energy and power densities. In this work, we analyzed the energy densities of Li-garnet all-solid-state batteries based solely on LLZO SSE by modeling their Ragone plots using LiCoO
as the model cathode material. This assessment allowed us to identify values of the LLZO thickness, cathode areal capacity, and LLZO content in the solid-state cathode required to match the energy density of conventional lithium-ion batteries (ca. 180 Wh kg
and 497 Wh L
) at the power densities of 200 W kg
and 600 W L
, corresponding to ca. 1 h of battery discharge time (1C). We then discuss key challenges in the practical deployment of LLZO SSE in the fabrication of Li-garnet all-solid-state batteries.
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