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RISS 인기검색어
- 검색키워드
- 저자 : M.F. Toney (검색결과 4 건)
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Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide
Gold-Parker, Aryeh,Gehring, Peter M.,Skelton, Jonathan M.,Smith, Ian C.,Parshall, Dan,Frost, Jarvist M.,Karunadasa, Hemamala I.,Walsh, Aron,Toney, Michael F. National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.47
<▼1><P><B>Significance</B></P><P>Hybrid organic–inorganic perovskites are a promising class of materials for efficient and low-cost solar cells. Unlike conventional inorganic semiconductors such as silicon and gallium arsenide, hybrid perovskites feature significant dynamic disorder in their crystal structure. This dynamic disorder can be broadly classified into lattice vibrations (phonons) and molecular rotations. Phonons interact with charge carriers through electron–phonon coupling, which has substantial impacts on the operation of solar cells. Our study shows that acoustic phonons, the type responsible for transmitting heat in conventional semiconductors, have extraordinarily short lifetimes in the archetypal hybrid perovskite methylammonium lead iodide. These short lifetimes have direct implications on the cooling and transport of electrons and reflect a key difference between hybrid perovskites and conventional photovoltaic semiconductors.</P></▼1><▼2><P>Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.</P></▼2>
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Ko, Sangwon,Kim, Do Hwan,Ayzner, Alexander L.,Mannsfeld, Stefan C. B.,Verploegen, Eric,Nardes, Alexander M.,Kopidakis, Nikos,Toney, Michael F.,Bao, Zhenan American Chemical Society 2015 Chemistry of materials Vol.27 No.4
<P>We observed a thermotropic phase transition in poly[3,4-dihexyl thiophene-2,2′:5,6′-benzo[1,2-b:4,5-b′]dithiophene] (<B>PDHBDT</B>) thin films accompanied by a transition from a random orientation to an ordered lamellar phase via a nearly hexagonal lattice upon annealing. We demonstrate the effect of temperature-dependent molecular packing on charge carrier mobility (μ) in organic field-effect transistors (OFETs) and photovoltaic characteristics, such as exciton diffusion length (<I>L</I><SUB>D</SUB>) and power conversion efficiency (PCE), in organic solar cells (OSCs) using <B>PDHBDT</B>. The μ was continuously improved with increasing annealing temperature and <B>PDHBDT</B> films annealed at 270 °C resulted in a maximum μ up to 0.46 cm<SUP>2</SUP>/(V s) (μ<SUB>avg</SUB> = 0.22 cm<SUP>2</SUP>/(V s)), which is attributed to the well-ordered lamellar structure with a closer π–π stacking distance of 3.5 Å as shown by grazing incidence-angle X-ray diffraction (GIXD). On the other hand, <B>PDHBDT</B> films with a random molecular orientation are more effective in photovoltaic devices than films with an ordered hexagonal or lamellar phase based on current–voltage characteristics of <B>PDHBDT</B>/C60 bilayer solar cells. This observation corresponds to an enhanced dark current density (<I>J</I><SUB>D</SUB>) and a decreased <I>L</I><SUB>D</SUB> upon annealing. This study provides insight into the dependence of charge transport and photovoltaic characteristics on molecular packing in polymer semiconductors, which is crucial for the management of charge and energy transport in a range of organic optoelectronic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-4/cm503773j/production/images/medium/cm-2014-03773j_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm503773j'>ACS Electronic Supporting Info</A></P>
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Structure of palladium nanoclusters for hydrogen gas sensors
K.J. Stevens,B. Ingham,M.F. Toney,S.A. Brown,A. Lassesson 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4
Palladium nanoclusters produced by inert gas aggregation/magnetron sputtering are used as building blocks for the construction ofnano electronic devices with large surface to volume ratios that can be used as sensitive hydrogen gas sensors in fuel cells and in petro-chemical plants. X-ray diraction (XRD), extended X-ray absorption ne structure (EXAFS), and high resolution transmission electronmicroscopy (HRTEM) have been used to characterise the structure, lattice constant, particle diameter and oxide thickness of the palla-dium nanoclusters in order to understand the operation of these sensors. Grazing incidence XRD (GIXRD) of heat treated Pd clustershas shown that the palladanite structure forms at elevated temperatures.
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