A5072424049- X-ray Diffraction in Crystallography
- Perovskite Materials and Applications
- Crystallization and Solubility Studies
- Quantum Dots Synthesis And Properties
- Chalcogenide Semiconductor Thin Films
- 2D Materials and Applications
- Copper-based nanomaterials and applications
- Electronic and Structural Properties of Oxides
- Solid-state spectroscopy and crystallography
- Layered Double Hydroxides Synthesis and Applications
- Catalysis and Oxidation Reactions
- Catalytic Processes in Materials Science
- Advanced Thermoelectric Materials and Devices
- Conducting polymers and applications
- Advancements in Solid Oxide Fuel Cells
- Organic Light-Emitting Diodes Research
- Luminescence and Fluorescent Materials
- Acoustic Wave Resonator Technologies
- Gold and Silver Nanoparticles Synthesis and Applications
- Silicon and Solar Cell Technologies
- Advanced Photocatalysis Techniques
- Thermal Expansion and Ionic Conductivity
- Magnetic and transport properties of perovskites and related materials
- Terahertz technology and applications
- Thermal properties of materials
Massachusetts Institute of Technology
2016-2023
Frontier Energy (United States)
2017
Organic–inorganic perovskites have been shown to excellent optoelectronic properties. Further, layered demonstrated, utilizing quantum confinement achieve emission blue-shifted from the bulk band gap. Here, we tune this blue-shift build LEDs that span visible spectrum. We demonstrate electroluminescence red-shifted layers dominates mixed-thickness devices and addition of excess ligand is necessary drive toward layers. By tuning thickness layers, with blue lead bromide system orange iodide...
We report the cooling-induced crystallization of layered two-dimensional (2D) lead halide perovskites with controllable inorganic quantum-well thicknesses (n = 1, 2, 3, and 4), organic-spacer chain lengths (butyl-, pentyl-, hexylammonium), A-site cations (methylammonium formamidinium), anions (iodide bromide). Using single-crystal X-ray diffraction, we refined crystal structures for iodide family as a function these compositional parameters across their temperature-dependent phase...
Broadband emission in lead iodide 2D perovskites has been alternately attributed to self-trapped excitons (STEs) or permanent structural defects and/or impurities. Here, we investigate six different multilayered (n > 1) as a function of sample temperature from 5 300 K. We distinguish shallow defect-associated broad near-infrared (NIR) spectral feature, which assign an STE through subgap photoexcitation experiments. When varied the thickness = 2, 3, 4), A-site cation (methylammonium vs...
Hybrid two-dimensional (2D)-layered perovskites with formula A2PbX4, where X = I, Br, or Cl and A is an ammonium-terminated organic cation, have attracted interest due to their tunable optoelectronic properties. In particular, the nature of interactions between tightly bound excitons polar inorganic–organic lattice in these dielectrically quantum-confined materials has been subject intense investigation. Using a combination resonant impulsive-stimulated Raman scattering, nonresonant...
We report the low-frequency Raman spectrum (ω = 10 cm−1–150 cm−1) of a wide variety alkylammonium iodide based 2D lead halide perovskites (2D LHPs) as function A-site cation (MA methylammonium and FA formamidinium), octahedral layer thickness (n 2–4), organic spacer chain length (butyl-, pentyl-, hexyl-), sample temperature (T 77 K–293 K). Using density functional theory calculations under harmonic approximation for n 2 BA:MAPbI, we assign several longitudinal/transverse optical phonon modes...
Hybrid quantum dot (QD)/transition metal dichalcogenide (TMD) heterostructures are attractive components of next generation optoelectronic devices, which take advantage the spectral tunability QDs and charge exciton transport properties TMDs. Here, we demonstrate tunable electronic coupling between CdSe monolayer WS2 using variable length alkanethiol ligands on QD surface. Using femtosecond time-resolved second harmonic (SHG) microscopy, show that electron transfer from photoexcited to...
We investigate the phase behavior of two-dimensional (CxH2x+1NH3)2[(MA,FA)PbI3]n−1PbI4 layered perovskites near room temperature (−20 °C to +100 °C) as a function octahedral layer thickness (n = 1, 2, 3, 4), alkylammonium chain length (butyl, pentyl, and hexyl), identity small organic cation (methylammonium formamidinium). Using differential scanning calorimetry X-ray diffraction, we observe reversible first-order transition corresponding partial melting chains separating perovskite layers....
Recent experimental and theoretical results have highlighted the surprisingly dominant role of acoustic phonons in regulating dynamic processes nanocrystals. While it has been known for many years that phonon frequencies nanocrystals depend on their size, strategies tuning energy at a given fixed size were not available. Here, we show colloidal quantum dots (QDs) can be tuned through choice surface ligand. Using low-frequency Raman spectroscopy, explore dependence l = 0 resonance CdSe QDs...
Layered hybrid perovskites exhibit emergent physical properties and exceptional functional performances, but the coexistence of lattice order structural disorder severely hinders our understanding these materials. One unsolved problem regards how dynamics are affected by dimensional engineering inorganic frameworks their interaction with molecular moieties. Here, we address this question using a combination spontaneous Raman scattering, terahertz spectroscopy, simulations. This approach...
Characterization efforts of core/shell and core/multishell nanocrystals have struggled to quantitatively evaluate the interface width between core shell materials despite its importance in their optoelectronic properties. Here, we demonstrate a scanning transmission electron microscopy (STEM) method for measuring radial elemental composition two spherical nanocrystal systems, Ge/Si CdSe/CdS/ZnS core/double-shell nanocrystals. By fitting model-based distributions elements measured...
We report the cooling-induced crystallization of layered two-dimensional lead halide perovskites with controllable inorganic quantum-well thickness ( n = 1, 2, 3, 4) , organic spacer chain length (butyl-, pentyl-, hexylammonium), A-site cation (methylammonium, formamidinium), and anion (iodide, bromide). crystal structures for iodide family as a function these compositional parameters, across their temperature dependent phase transitions. In general, lower symmetry structures, increasing...
Electronic trap states limit the overall power conversion efficiency of quantum dot (QD) solar cells by inhibiting charge carrier transport and reducing open-circuit voltage. Here, we explore dynamic interaction carriers between band edge sub-band using broadband transient absorption spectroscopy. In monodisperse arrays 4-5 nm diameter PbS QDs, observe an optically active state ~100-200 meV below that occurs at a frequency 1 in ~2500 QDs. Uncoupled QD solids with oleic acid ligands show...
We report the cooling-induced crystallization of layered two-dimensional lead halide perovskites with controllable inorganic quantum-well thickness (<i>n</i> = 1, 2, 3, 4)<i>,</i> organic spacer chain length (butyl-, pentyl-, hexylammonium), A-site cation (methylammonium, formamidinium), and anion (iodide, bromide). crystal structures for iodide family as a function these compositional parameters, across their temperature dependent phase transitions. In general, lower...
We report measurements of the heat capacity and cross-plane thermal conductivity 2D (CxH2x+1NH3)2[MAPbBr3]n-1PbBr4 (MA = methylammonium) lead bromide perovskites (2D LHPs) at room temperature as a function both octahedral layer thickness (n 1,2,3) organic spacer chain length (x=4,5,6,7,8) using differential scanning calorimetry (DSC) frequency domain thermoreflectance (FDTR) respectively. observe ultralow conductivities (0.18-0.51 W/m K) for all LHPs studied, but surprisingly minimal...
Organic-inorganic perovskites have revolutionized the optoelectronics field, providing materials with a wide range of properties for solving numerous applications. Indeed, much recent work has been focused on nanostructured perovskites, quantum dots, nanowires, and nanoplatelets showing tremendous potential. Here, we utilize unique tunability 2D perovskite to build LEDs that span visible spectrum. Quantum confinement in z direction drives significant blueshift, allowing blue devices...
Electronic trap states limit the overall power conversion efficiency of quantum dot (QD) solar cells by inhibiting charge carrier transport and reducing open-circuit voltage. Here, we explore dynamic interaction carriers between band edge sub-band using broadband transient absorption spectroscopy. In monodisperse arrays 4-5 nm diameter PbS QDs, observe an optically active state ~100-200 meV below that occurs at a frequency 1 in ~2500 QDs. Uncoupled QD solids with oleic acid ligands show...