A5080398727- Perovskite Materials and Applications
- Organic Electronics and Photovoltaics
- Solid-state spectroscopy and crystallography
- Chalcogenide Semiconductor Thin Films
- Conducting polymers and applications
- Quantum Dots Synthesis And Properties
- Molecular Junctions and Nanostructures
- Optical properties and cooling technologies in crystalline materials
- Fullerene Chemistry and Applications
- Semiconductor materials and interfaces
- Electronic and Structural Properties of Oxides
- Machine Learning in Materials Science
- Photochemistry and Electron Transfer Studies
- Organic Light-Emitting Diodes Research
- Semiconductor materials and devices
- Advanced Thermoelectric Materials and Devices
- Thermal Expansion and Ionic Conductivity
- Magnetic and transport properties of perovskites and related materials
- ZnO doping and properties
- Thin-Film Transistor Technologies
- Organic and Molecular Conductors Research
- Optical and Acousto-Optic Technologies
- Synthesis and Properties of Aromatic Compounds
- Copper-based nanomaterials and applications
- Force Microscopy Techniques and Applications
Imperial College London
2016-2025
Stanford University
2022
King Abdullah University of Science and Technology
2022
The Francis Crick Institute
2022
London Biofoundry
2022
University of Oxford
2022
King's College London
2018-2019
University of Bath
2007-2019
Yonsei University
2019
Thomas Young Centre
2019
Solar cells based on organic–inorganic halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behaviour such as current–voltage hysteresis and a low-frequency giant dielectric response. Ionic transport has been suggested to be an important factor contributing these effects; however, the chemical origin of this mobile species are unclear. Here, activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) derived from...
The performance of organometallic perovskite solar cells has rapidly surpassed that both conventional dye-sensitized and organic photovoltaics. High-power conversion efficiency can be realized in mesoporous thin-film device architectures. We address the origin this success context materials chemistry physics bulk as described by electronic structure calculations. In addition to basic optoelectronic properties essential for an efficient photovoltaic (spectrally suitable band gap, high optical...
Abstract Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic neutron scattering measurements showing that dipolar CH 3 NH + ions reorientate between faces, corners or edges of pseudo-cubic lattice cages in PbI crystals with a room temperature residence time ∼14 ps. Free rotation, π-flips and ionic diffusion are ruled out within 1–200-ps window....
We report a model describing the molecular orientation disorder in CH3NH3PbI3, solving classical Hamiltonian parametrised with electronic structure calculations, nature of motions informed by ab-initio dynamics. investigate temperature and static electric field dependence equilibrium ferroelectric (molecular) domain resulting polarisability. A rich twinned dipoles is observed, strongly varying as function applied field. propose that internal electrical fields associated microscopic...
The hybrid halide perovskite ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$ exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$. equilibrium structures compare well to solutions temperature-dependent powder neutron diffraction. By following the normal...
The structure of black formamidinium lead halide, α-[HC(NH2)2]PbI3, at 298 K has been refined from high resolution neutron powder diffraction data and found to adopt a cubic perovskite unit cell, = 6.3620(8) Å. trigonal planar [HC(NH2)2]+ cations lie in the central mirror plane cell with disordered over 12 possible sites arranged so that C–H bond is directed into cube face, whereas −NH2 groups hydrogen (NH···I 2.75–3.00 Å) iodide atoms [PbI3]− framework. High atomic displacement parameters...
Organic-inorganic semiconductors, which adopt the perovskite crystal structure, have perturbed landscape of contemporary photovoltaics research. In this Account, we discuss internal motion methylammonium lead iodide (CH$_3$NH$_3$PbI$_3$) and formamidinium ([CH(NH$_2$)$_2$]PbI$_3$), covering: (i) molecular rotation-libration in cuboctahedral cavity; (ii) drift diffusion large electron hole polarons; (iii) transport charged ionic defects. These processes give rise to a range properties that...
Ferroelectric materials offer opportunities for unconventional solar energy conversion.
Polymer/small molecule binaries, such as P3HT:PC61BM display eutectic phase behavior with optimum photovoltaic performance at slightly hypoeutectic compositions (with respect to polymer content). Such blends readily solidify into a finely phase-separated matrix surrounding primary crystals of the small-molecular species. The resulting large interfacial area and component connectivity is desirable microstructure for bulk-heterojunction solar cells.
Methylammonium lead iodide perovskites are considered direct bandgap semiconductors. Here we show that in fact they present a weakly indirect 60 meV below the transition. This is consequence of spin-orbit coupling resulting Rashba-splitting conduction band. The nature explains apparent contradiction strong absorption and long charge carrier lifetime. Under hydrostatic pressure from ambient to 325 MPa, Rashba splitting reduced due induced ordering crystal structure. becomes increasingly more...
The introduction of a mobile and polarized organic moiety as cation in 3D lead-iodide perovskites brings fascinating optoelectronic properties to these materials. extent the time scales orientational mobility molecular mechanism behind its motion remain unclear, with different experimental computational approaches providing very qualitative quantitative description dynamics. Here we use ultrafast 2D vibrational spectroscopy methylammonium (MA) lead iodide directly resolve rotation cations...
Lead halide perovskites such as methylammonium lead triiodide (MAPI) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this solution processable material works so well is currently missing. Previous research has revealed that MAPI possesses multiple forms static disorder regardless preparation method, which surprising in light its excellent performance. Using high energy resolution inelastic X-ray (HERIX) scattering, we measure...
Valence band energies of three organic–inorganic perovskites are compared from electronic structure theory.
Raman and THz spectra of CH<sub>3</sub>NH<sub>3</sub>PbX<sub>3</sub> interpreted with a catalogue computed vibrations their influence on heat electrical transport.
Two novel indacenodithiophene (IDT) based donor–acceptor conjugated polymers for use in organic field effect transistors and photovoltaic devices are synthesized characterized. The of inclusion two fluorine atoms on the acceptor portion polymer is thoroughly investigated via a range techniques. inductively withdrawing mesomerically donating properties result decrease highest occupied molecular orbital (HOMO), with little lowest unoccupied (LUMO) as demonstrated through density functional...
Lead halide perovskite semiconductors are soft, polar, materials. The strong driving force for polaron formation (the dielectric electron-phonon coupling) is balanced by the light band effective-masses, leading to a strongly-interacting large-polaron. A first-principles prediction of mobility would help understand fundamental limits. Theories need consider (rather than free-carrier) state due interactions. In this material we expect that at room temperature polar-optical phonon mode...
The local crystal structures of many perovskite-structured materials deviate from the average space-group symmetry. We demonstrate, lattice-dynamics calculations based on quantum chemical force constants, that all cesium-lead and cesium-tin halide perovskites exhibit vibrational instabilities associated with octahedral titling in their high-temperature cubic phase. Anharmonic double-well potentials are found for zone-boundary phonon modes compounds barriers ranging 108 to 512 meV. well depth...
Halide perovskite semiconductors and solar cells respond to electric fields in a way that varies across time length scales. We discuss the microscopic processes give rise macroscopic polarization of these materials, ranging from optical vibrational response transport ions electrons. The strong frequency dependence dielectric permittivity can be understood by separating static constant into its constituents, including orientational due rotating dipoles, which connects theory with experimental...
Abstract Hyperfluorescence shows great promise for the next generation of commercially feasible blue organic light-emitting diodes, which eliminating Dexter transfer to terminal emitter triplet states is key efficiency and stability. Current devices rely on high-gap matrices prevent transfer, unfortunately leads overly complex from a fabrication standpoint. Here we introduce molecular design where ultranarrowband emitters are covalently encapsulated by insulating alkylene straps. Organic...
The performance of an organic photovoltaic cell depends critically on the mobility charge carriers within constituent molecular semiconductor materials. However, a complex combination phenomena that span range length and time scales control transport in disordered semiconductors. As result, it is difficult to rationalize properties terms material parameters. Until now, efforts improve mobilities semiconductors have proceeded largely by trial error rather than through systematic design....
Efficient charge pair generation is observed in many organic photovoltaic (OPV) heterojunctions, despite nominal electron-hole binding energies which greatly exceed the average thermal energy. Empirically, efficiency of this process appears to be related choice donor and acceptor materials, resulting sequence excited state energy levels structure interface. In order establish a suitable physical model for process, range different theoretical studies have addressed nature interfacial states,...
Forming a four-component compound from the first 103 elements of periodic table results in more than 1012 combinations. Such materials space is intractable to high-throughput experiment or first-principle computation. We introduce framework address this problem and quantify how many can exist. apply principles valency electronegativity filter chemically implausible compositions, which reduces inorganic quaternary 1010 demonstrate that estimates band gaps absolute electron energies be made...
Lattice vibrations in CH$_3$NH$_3$PbI$_3$ are strongly interacting, with double well instabilities present at the Brillouin zone boundary. Analysis within a first-principles lattice dynamics framework reveals anharmonic potentials short phonon quasi-particle lifetimes and mean-free paths. The behaviour is distinct from inorganic semiconductors GaAs CdTe where three-phonon interaction strengths three orders of magnitude smaller. implications for applications hybrid halide perovskites arising...
Chiral molecules exist as pairs of nonsuperimposable mirror images; a fundamental symmetry property vastly underexplored in organic electronic devices. Here, we show that field-effect transistors (OFETs) made from the helically chiral molecule 1-aza[6]helicene can display up to an 80-fold difference hole mobility, together with differences thin-film photophysics and morphology, solely depending on whether single handedness or 1:1 mixture left- right-handed is employed under analogous...