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Quantum confinement in PbI2 nanodisks prepared with cucurbit[7]uril

SANTOS, Erick M. S. dos; PEREIRA, Lourivaldo S.; DEMETS, Grégoire J.-F.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.803022%
This work presents an alternative route for the preparation of heavy metal iodide nanoparticles, particularly lead iodide nanodisks (ca. 50-340 × 7 Å, diameter × thickness), using the macrocycle cucurbit[7]uril as a synthetic template and stabilizing agent. These nanoparticles exhibit an optical-gap blue shift consistent with their small size and 1D quantum confinement. Their thicknesses are compatible with an exfoliated single layer of lead iodide, indicating that cucurbit[7]uril, preventing the stacking and formation of tactoids, thus limiting nanoparticles growth in the z direction. The structure, morphology and properties of these disks were analyzed by X-ray powder diffractometry (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), scanning electron microscopy with analysis of energy dispersive X-ray fluorescence (SEM-EDS) and high resolution transmission electron microscopy (HRTEM).; Este trabalho apresenta uma rota alternativa para a preparação de nanodiscos de iodeto de chumbo (ca. 50-340 × 7Å, diâmetro × espessura) utilizando o macrocíclico cucurbit[7]urila como molde de síntese e agente estabilizante. Estas nanopartículas apresentam um deslocamento para o azul de gap óptico consistente com seu tamanho reduzido e confinamento quântico 1D. Suas espessuras são compatíveis com a de uma camada de iodeto de chumbo esfoliado...

Filmes finos de iodeto de chumbo (PbI2)produzidos por spray pyrolysis ; Thin films of lead iodide (PbI2) produced by spray pyrolysis

Condeles, José Fernando
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 31/10/2003 PT
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Pesquisadores em todo o mundo buscam métodos alternativos que minimizem o tempo de deposição de filmes finos semicondutores cotados como promissores candidatos em aplicações médicas como detectores de raios-X em radiografias digitais. O iodeto de chumbo (PbI2) é considerado, entre outros, como um bom candidato para a fabricação de detectores usados à temperatura ambiente. Outros pesquisadores fabricaram protótipos de detectores usando esse material. Seus experimentos mostraram alta resolução e sensibilidade para imagens em tempo real, mostrando que o material possui potencialidade para aplicações médicas futuramente. Não obstante, uma das desvantagens de seus métodos é o longo tempo necessário para a deposição na fabricação de filmes finos. Este trabalho apresenta uma nova metodologia usada para a deposição de filmes finos de iodeto de chumbo (PbI2). O método alternativo de crescimento dos filmes é chamado de spray pyrolysis. A técnica possui uma vantagem intrínseca pelo fato de a deposição ser facilmente expandida para grandes áreas de substrato que é desejado nas linhas de produção industrial. O pó de iodeto de chumbo foi dissolvido em água deionizada a 100ºC (água em ebulição) onde a solubilidade é maior que à temperatura ambiente. Após a dissolução do pó...

Filmes finos de iodeto de chumbo como detector de raios-X para imagens médicas; Lead Iodide Thin Films as X-ray detectors for Medical Imaging

Condeles, José Fernando
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/10/2007 PT
Relevância na Pesquisa
67.670625%
Nos últimos anos, acentuou-se o interesse em materiais semicondutores com alto número atômico e larga banda de energia proibida para aplicações na detecção de radiação ionizante à temperatura ambiente, usando o método direto de detecção. Alguns materiais como o PbI2, HgI2, TlBr, CdTe and CdZnTe são bons fotocondutores e podem ser usados à temperatura ambiente. Como um bom candidato, o PbI2 apresenta uma banda de energia proibida acima de 2,0 eV, o qual quando operando à temperatura ambiente apresenta um baixo ruído, baixa corrente de fuga e alta coleta de cargas. O alto poder de frenamento da radiação ionizante é devido ao alto número atômico e alta densidade. Pesquisadores buscam métodos alternativos que minimizem o tempo de deposição e barateiem o custo dos filmes finos de materiais semicondutores candidatos em aplicações médicas, como detector de raios-X à temperatura ambiente para radiografias digitais. Neste sentido, apresentamos dois métodos para a deposição de filmes finos policristalinos de iodeto de chumbo (PbI2). As técnicas de spray pyrolysis (SP) e evaporação de solvente em estufa (ES) foram usadas para a fabricação de filmes finos de PbI2 com relativo baixo tempo de deposição. A técnica de SP foi adotada com o uso de água milli-Q e N.N-dimetilformamida (DMF) como solventes...

Fabricação e caracterização de filmes finos de iodeto de chumbo e cristais de iodeto de mercúrio; Fabricatins and Characterization of lead iodide films and mercury iodide crystals.

Caldeira Filho, Ademar Marques
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 09/05/2008 PT
Relevância na Pesquisa
68.28032%
Nos últimos anos, acentuou-se o interesse em materiais semicondutores com alto número atômico e alto gap de energia para aplicações na detecção de radiação ionizante à temperatura ambiente, usando o método direto de detecção. Este trabalho apresentara as características de dois materiais semicondutores na forma de filme para o iodeto de chumbo e de cristal milimétrico para o iodeto de mercúrio. Os filmes foram depositados a partir da evaporadora térmica construída no próprio departamento e caracterizados em função de três distâncias de deposição. O melhor filme obtido foi produzido a 5 cm de distância da fonte, apresentando valores de gap de energia de 2,39 eV e energia de ativação de 1,1 eV. Com o aumento dessa distância as propriedades estruturais, ópticas e elétricas se deterioram, inclusive com variação da composição do material. Os cristais de iodeto de mercúrio foram dissolvidos no solvente orgânico N-N Dimetilformamida e crescidos utilizando a técnica de deposição de solvente. Diferentes taxas de crescimento foram usadas para o crescimento dos cristais. Os melhores resultados foram obtidos para crescimento na estufa a 80ºC, produzindo filmes com gap de energia de 2,2 eV e resistividade da ordem de 108 ?.cm...

Desenvolvimento de cristais baseados em iodeto de Césio para aplicação como detectores de radiação; Development of crystals based in cesium iodide for application as radiation detectors

Pereira, Maria da Conceição Costa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/06/2006 PT
Relevância na Pesquisa
37.336797%
Cintiladores inorgânicos com tempo de decaimento de luminescência rápido, densidade alta e boa produção de luz têm sido objeto de estudos para aplicações em física nuclear, física de energias altas, tomografia nuclear e outros campos da ciência e da engenharia. Cristais de cintilação baseados em iodeto de césio (Csl) são materiais que apresentam higroscopia relativamente baixa, número atômico alto, fácil manuseio e custo baixo, características que favorecem o seu uso como detectores de radiação. Neste trabalho descreve-se a obtenção de cristais Csl puro, Csl:Br e Csl:Pb, utilizando-se a técnica de Bridgman. A concentração do elemento dopante bromo (Br) foi estudada no intervalo de 1,5x10-1 M a 10-2 M e o elemento chumbo (Pb) no intervalo de 10-2 M a 5x10-4 M. Para avaliar os cintiladores desenvolvidos foram efetuadas medidas sistemáticas de emissão de luminescência e tempo de decaimento de luminescência para a radiação gama, ensaios de transmitância óptica, ensaios de microdureza Vickers, determinações da distribuição dos dopantes ao longo dos cristais crescidos e análise da resposta dos cristais à radiação gama no intervalo de energia de 350 keV a 1330 keV e partículas alfa provenientes de fonte de 241Am com energia de 5...

Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system

Gomes Neto, José A; Oliveira, Adriana P; Freshi, Gian P.G; Dakuzaku, Carolina S; De Moraes, Mercedes
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 497-503
ENG
Relevância na Pesquisa
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A new strategy for minimization of Cu2+ and Pb2+ interferences on the spectrophotometric determination of Cd2+ by the Malachite green (MG)-iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd2+ in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO3, 0.1% (v/v) H2SO4 and 0.5 M NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd2+ is extracted as CdCl4/2-. Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb2+ and Cu2+ levels up to 50 and 250 mg 1-1, respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00-50.0 μg Cd 1-1 range (r2 = 0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 μg Cd 1-1. The accuracy was checked for cadmium determination in standard reference materials...

A flow system for the spectrophotometric determination of lead in different types of waters using ion-exchange for pre-concentration and elimination of interferences

Mesquita, Raquel B.R.; Fernandes, Sílvia M.V.; Rangel, António O.S.S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2004 ENG
Relevância na Pesquisa
37.230012%
A flow system for the spectrophotometric determination of lead in natural and waste waters is proposed. The determination is based on the colorimetric reaction between malachite green and iodide, followed by the formation of a ternary complex between those reagents and lead cations. The developed flow system includes a lead pre-concentration step in a column packed with a cationic resin (Chelex 100) operating in a sequential injection mode. To improve the mixture of sample and reagents, a flow injection approach was adopted for the colorimetric determination. This way a hybrid flow system, involving both sequential and flow injection concepts was designed. Another feature of the proposed system is the efficient elimination of major interferent species, such as cadmium and copper. The elimination of cadmium interference is obtained by complexing Cd2+ with chloride and retaining the formed negatively charged complexes in an anionic resin, AG1 X-8. As for copper, with the presence of both ionic resins as well as the conditions for cadmium elimination, it no longer acts as an interferent. Different ranges of lead concentration (50–300 and 300–1000 g l−1) can be determined with minor changes in the controlling software, useful for application to both natural and waste waters. Therefore...

Spectrophotometic flow injection determination of lead in port wine using in-line ion-exchange concentration

Lopes, Teresa I. M. S.; Rangel, António O. S. S.; Sartini, Raquel B.; Zagatto, Elias A. G.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //1996 ENG
Relevância na Pesquisa
37.16726%
A flow injection system with in-line ion exchange is proposed for the spectrophotometric determination of lead in Port wine. A Chelex-100 resin mini-column (200–400 mesh) is used for lead concentration, and the chromogenic reaction is based on the formation of a ternary complex between lead, Malachite Green and iodide. Forty-five digested wine samples can be run per hour (25–500 µg l–1 Pb) and results are comparable to those obtained by ETAAS. Other features are the measurement precision (RSDs lower than 2.6%), a detection limit of 12 µg l–1 and a sampling rate of 45 h–1.

Quantum confinement in PbI2 nanodisks prepared with cucurbit[7]uril

Santos,Erick M. S. dos; Pereira,Lourivaldo S.; Demets,Grégoire J.-F.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2011 EN
Relevância na Pesquisa
47.803022%
This work presents an alternative route for the preparation of heavy metal iodide nanoparticles, particularly lead iodide nanodisks (ca. 50-340 × 7 Å, diameter × thickness), using the macrocycle cucurbit[7]uril as a synthetic template and stabilizing agent. These nanoparticles exhibit an optical-gap blue shift consistent with their small size and 1D quantum confinement. Their thicknesses are compatible with an exfoliated single layer of lead iodide, indicating that cucurbit[7]uril, preventing the stacking and formation of tactoids, thus limiting nanoparticles growth in the z direction. The structure, morphology and properties of these disks were analyzed by X-ray powder diffractometry (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), scanning electron microscopy with analysis of energy dispersive X-ray fluorescence (SEM-EDS) and high resolution transmission electron microscopy (HRTEM).

Growth of mercuric iodide crystals

Ugucioni,J. C.; Ferreira,M.; Fajardo,F.; Mulato,M.
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
Relevância na Pesquisa
37.325366%
Mercuric Iodide (HgI2) is a semiconductor candidate for the construction of X- and gamma-ray detectors for digital medical imaging due to its high atomic number (Z Hg = 80, Z I = 53). Also, HgI2 has a wide optical band-gap (2.13 eV) and high photon absorption coefficient for high-energy radiation. Different structures can lead to varying electrical and optical properties of the final material. In this work, HgI2 crystals were produced by the solvent evaporation technique. The solvents used were ethanol (solubility around 20 mg/ml at 25ºC), ether (solubility around 3.5 mg/ml at 25ºC) and acetone (solubility around 24mg/ml at 25ºC). The evaporation conditions were varied in order to produce different final crystals. The Bérnard cells are responsible for crystallites formation due to the Bérnard-Maragoni convection in the liquid. Millimeter-sized crystals can be obtained as seen by Scanning Electron Microscopy.

Stoichiometry, surface and structural characterization of lead iodide thin films

Condeles,J. F.; Lofrano,R. C. Z.; Rosolen,J. M.; Mulato,M.
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
Relevância na Pesquisa
67.670625%
In this work we present the structural properties and stoichiometry analysis of thin films of lead iodide (PbI2). This material is a very promising semiconductor material for the development of X-ray detectors in digital medical imaging. An alternative deposition method called Spray Pyrolysis was used. We discuss the main advantages and limitations of the deposition process comparing three different starting material powders. Extra iodine atmosphere during deposition and the effect of post-deposition thermal treatment is also discussed. The structural properties were studied by X-ray diffraction, Atomic Force Microscopy (AFM), Scanning Electronic Microscopy (SEM) and stoichiometry analysis were performed using Energy Dispersive Spectroscopy (EDS).

Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%

Kim, Hui-Seon; Lee, Chang-Ryul; Im, Jeong-Hyeok; Lee, Ki-Beom; Moehl, Thomas; Marchioro, Arianna; Moon, Soo-Jin; Humphry-Baker, Robin; Yum, Jun-Ho; Moser, Jacques E.; Grätzel, Michael; Park, Nam-Gyu
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 21/08/2012 EN
Relevância na Pesquisa
47.551943%
We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH3NH3)PbI3 as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI2 and deposited onto a submicron-thick mesoscopic TiO2 film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (JSC) exceeding 17 mA/cm2, an open circuit photovoltage (VOC) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH3NH3)PbI3 NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO2 film. The use of a solid hole conductor dramatically improved the device stability compared to (CH3NH3)PbI3 -sensitized liquid junction cells.

Lead iodide perovskite light-emitting field-effect transistor

Chin, Xin Yu; Cortecchia, Daniele; Yin, Jun; Bruno, Annalisa; Soci, Cesare
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 25/06/2015 EN
Relevância na Pesquisa
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Despite the widespread use of solution-processable hybrid organic–inorganic perovskites in photovoltaic and light-emitting applications, determination of their intrinsic charge transport parameters has been elusive due to the variability of film preparation and history-dependent device performance. Here we show that screening effects associated to ionic transport can be effectively eliminated by lowering the operating temperature of methylammonium lead iodide perovskite (CH3NH3PbI3) field-effect transistors. Field-effect carrier mobility is found to increase by almost two orders of magnitude below 200 K, consistent with phonon scattering-limited transport. Under balanced ambipolar carrier injection, gate-dependent electroluminescence is also observed from the transistor channel, with spectra revealing the tetragonal to orthorhombic phase transition. This demonstration of CH3NH3PbI3 light-emitting field-effect transistors provides intrinsic transport parameters to guide materials and solar cell optimization, and will drive the development of new electro-optic device concepts, such as gated light-emitting diodes and lasers operating at room temperature.

Ionic transport in hybrid lead iodide perovskite solar cells

Eames, Christopher; Frost, Jarvist M.; Barnes, Piers R. F.; O'Regan, Brian C.; Walsh, Aron; Islam, M. Saiful
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 24/06/2015 EN
Relevância na Pesquisa
47.551943%
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 to these effects; however, the chemical origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current–voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and experimental study suggest that hybrid halide perovskites are mixed ionic–electronic conductors, a finding that has major implications for solar cell device architectures.

Gap energy studied by optical transmittance in lead iodide monocrystals grown by Bridgman's Method

Veissid,N.; An,C.Y.; Silva,A. Ferreira da; Souza,J.I. Pinto de
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/1999 EN
Relevância na Pesquisa
67.87606%
The bandgap energy as a function of temperature has been determined for lead iodide. The monocrystal was obtained in a vacuum sealed quartz ampoule inside a vertical furnace by Bridgman's method. The optical transmittance measurement enables to evaluate the values of Eg. By a fitting procedure of Eg as a function of temperature is possible to extract the parameters that govern its behavior. The variation of Eg with temperature was determined as: Eg(T) = Eg(0) - aT2/(a + T), with: Eg(0) = (2.435 ± 0.008) eV, a = (8.7 ± 1.3) x 10-4 eV/K and a = (192 ± 90) K. The bandgap energy of lead iodide at room temperature was found to be 2.277 ± 0.007 eV.

Methylammonium fragmentation in amines as source of localized trap levels and the healing role of Cl in Hybrid Lead-Iodide Perovskites

Delugas, Pietro; Filippetti, Alessio; Mattoni, Alessandro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/05/2015
Relevância na Pesquisa
47.336797%
The resilience to deep traps and localized defect formation is one of the important aspects that qualify a material as suited photo-absorber in solar cell devices. Here we investigate by ab-initio calculations the fundamental physics and chemistry of a number of possible localized defects in hybrid methylammonium lead-iodide perovskites. Our analysis encompasses a number of possible molecular fragments deriving from the dissociation of methylammonium. In particular, we found that in stoichiometric conditions both ammonia and methylamine molecules present lone-pair localized levels well within the perovskite band gap, while the radical cation CH$_2$NH$_3$$^+$ observed by EPR after irradiation injects partially-occupied levels into the band gap but only in $p$-type conditions. These defects are thus potentially capable to significantly alter absorption and recombination properties. Amazingly, we found that additional interstitial Cl is capable to remove these localized states from the band gap. These results are consistent with the observed improvement of photoabsorption properties due to the Cl inclusion in the solution processing.; Comment: preprint format, 23 pages, 10 figures

Lead Iodide Perovskite Light-Emitting Field-Effect Transistor

Chin, Xin Yu; Cortecchia, Daniele; Yin, Jun; Bruno, Annalisa; Soci, Cesare
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/01/2015
Relevância na Pesquisa
47.336797%
Despite the widespread use of solution-processable hybrid organic-inorganic perovskites in photovoltaic and light-emitting applications, determination of their intrinsic charge transport parameters has been elusive due to the variability of film preparation and history-dependent device performance. Here we show that screening effects associated to ionic transport can be effectively eliminated by lowering the operating temperature of methylammonium lead iodide perovskite (CH3NH3PbI3) field-effect transistors (FETs). Field-effect carrier mobility is found to increase by almost two orders of magnitude below 200 K, consistent with phonon scattering limited transport. Under balanced ambipolar carrier injection, gate-dependent electroluminescence is also observed from the transistor channel, with spectra revealing the tetragonal to orthorhombic phase transition. This first demonstration of CH3NH3PbI3 light-emitting FETs provides intrinsic transport parameters to guide materials and solar cell optimization, and will drive the development of new electro-optic device concepts, such as gated light emitting diodes and lasers operating at room temperature.

Persistent photovoltage in methylammonium lead iodide perovskite solar cells

Baumann, A.; Tvingstedt, K.; Heiber, M. C.; Väth, S.; Momblona, C.; Bolink, H. J.; Dyakonov, V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.336797%
Open circuit voltage decay measurements are performed on methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to investigate the charge carrier recombination dynamics. The measurements are compared to the two reference polymer-fullerene bulk heterojunction solar cells based on P3HT:PC60BM and PTB7:PC70BM blends. In the perovskite devices, two very different time domains of the voltage decay are found, with a first drop on a short time scale that is similar to the organic solar cells. However, two major differences are also observed. 65-70% of the maximum photovoltage persists on much longer timescales, and the recombination dynamics are dependent on the illumination intensity.; Comment: 5 pages, 3 figures

Real-Time Observation of Organic Cation Reorientation in Methylammonium Lead Iodide Perovskites

Bakulin, Artem A.; Selig, Oleg; Bakker, Huib J.; Rezus, Yves L. A.; M?ller, Christian; Glaser, Tobias; Lovrinic, Robert; Sun, Zhenhua; Chen, Zhuoying; Walsh, Aron; Frost, Jarvist M.; Jansen, Thomas L. C.
Fonte: ACS Publicador: ACS
Tipo: Article; accepted version
EN
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry Letters, copyright ? American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.5b01555; The introduction of a mobile and polarized organic moiety as a cation in 3D lead-iodide perovskites brings fascinating optoelectronic properties to these materials. The extent and the time scales of the orientational mobility of the organic cation and the molecular mechanism behind its motion remain unclear, with different experimental and computational approaches providing very different qualitative and quantitative description of the molecular dynamics. Here we use ultrafast 2D vibrational spectroscopy of methylammonium (MA) lead iodide to directly resolve the rotation of the organic cations within the MAPbI3 lattice. Our results reveal two characteristic time constants of motion. Using ab initio molecular dynamics simulations, we identify these as a fast (?300 fs) ?wobbling-in-a-cone? motion around the crystal axis and a relatively slow (?3 ps) jump-like reorientation of the molecular dipole with respect to the iodide lattice. The observed dynamics are essential for understanding the electronic properties of perovskite materials.; This work was supported by The Netherlands Organization for Scientific Research (NWO) through the ?Stichting voor Fundamenteel Onderzoek der Materie? (FOM) research program. A.A.B. also acknowledges a VENI grant from the NWO. A.A.B. is currently a Royal Society University Research Fellow. Z.S. and Z.C. acknowledge the ANR-2011-JS09-004-01-PvCoNano project and the EU Marie Curie Career Integration Grant (303824). A.A.B....

The Fabrication and Testing of a Lead Iodide Photovoltaic Cell

Greenberg, Keith
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
48.015225%
A new type of photovoltaic cell using lead iodide as the photosensitive element and aluminum and silver as electrodes was constructed and then tested for open circuit voltage, monochromatic quantum yield of short circuit current, and fill factor. A similar cell was also fabricated using the familiar merocyanine dye M-8 as the photosensitive element for use in a control experiment. Minimal open circuit voltages of not more than 26 mV were obtained for lead iodide while much larger photovoltaic parameters were obtained for M-8. The poor and impermanent performance of lead iodide relative to the organic control suggests that lead iodide is probably an inferior material for Schottky cells. At best it will have to be deposited under strikingly improved conditions not experimentally accessible in this research.