Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 20
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Phys Chem Lett ; 12(18): 4362-4367, 2021 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-33938752

RESUMO

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

2.
J Phys Chem Lett ; 11(16): 6772-6778, 2020 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-32689804

RESUMO

Hybrid perovskite solar cells attract a great deal of attention due to the feasibility of their low-cost production and their demonstration of impressive power conversion efficiencies (PCEs) exceeding 25%. However, the insufficient intrinsic stability of lead halides under light soaking and thermal stress impedes practical implementation of this technology. Herein, we show that the photothermal aging of a widely used perovskite light absorber such as MAPbI3 can be suppressed significantly by using polyvinylcarbazole (PVC) as a stabilizing agent. By applying a few complementary methods, we reveal that the PVC additive leads to passivation of defects in the absorber material. Introducing an optimal content of PVC into MAPbI3 delivers a PCE of 18.7% in combination with a significantly improved solar cell operational lifetime: devices retained ∼70% of the initial efficiency after light soaking for 1500 h, whereas the control samples without PVC degraded almost completely under the same conditions.

3.
ACS Appl Mater Interfaces ; 12(16): 19161-19173, 2020 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-32233360

RESUMO

We investigated the impact of a series of hole transport layer (HTL) materials such as Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiOx, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), and polytriarylamine (PTA) on photostability of thin films and solar cells based on MAPbI3, Cs0.15FA0.85PbI3, Cs0.1MA0.15FA0.75PbI3, Cs0.1MA0.15FA0.75Pb(Br0.15I0.85)3, and Cs0.15FA0.85Pb(Br0.15I0.85)3 complex lead halides. Mixed halide perovskites showed reduced photostability in comparison with similar iodide-only compositions. In particular, we observed light-induced recrystallization of all perovskite films except MAPbI3 with the strongest effects revealed for Br-containing systems. Moreover, halide and ß FAPbI3 phase segregations were also observed mostly in mixed-halide systems. Interestingly, coating perovskite films with the PCBM layer spectacularly suppressed light-induced growth of crystalline domains as well as segregation of Br-rich and I-rich phases or ß FAPbI3. We strongly believe that all three effects are promoted by the light-induced formation of surface defects, which are healed by adjacent PCBM coating. While comparing different hole-transport materials, we found that NiOx and PEDOT:PSS are the least suitable HTLs because of their interfacial (photo)chemical interactions with perovskite absorbers. On the contrary, polyarylamine-type HTLs PTA and PTAA form rather stable interfaces, which makes them the best candidates for durable p-i-n perovskite solar cells. Indeed, multilayered ITO/PTA(A)/MAPbI3/PCBM stacks revealed no aging effects within 1000 h of continuous light soaking and delivered stable and high power conversion efficiencies in solar cells. The obtained results suggest that using polyarylamine-type HTLs and simple single-phase perovskite compositions pave a way for designing stable and efficient perovskite solar cells.

4.
J Phys Chem Lett ; 11(7): 2630-2636, 2020 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-32178515

RESUMO

In this work, we report a comparative study of the gamma ray stability of perovskite solar cells based on a series of perovskite absorbers including MAPbI3 (MA = methylammonium), MAPbBr3, Cs0.15FA0.85PbI3 (FA = formamidinim), Cs0.1MA0.15FA0.75PbI3, CsPbI3, and CsPbBr3. We reveal that the composition of the perovskite material strongly affects the radiation stability of the solar cells. In particular, solar cells based on the MAPbI3 were found to be the most resistant to gamma rays since this perovskite undergoes rapid self-healing due to the special gas-phase chemistry analyzed with ab initio calculations. The fact that the solar cells based on MAPbI3 can withstand a 1000 kRad gamma ray dose without any noticeable degradation of the photovoltaic properties is particularly exciting and shifts the paradigm of research in this field toward designing more dynamic rather than intrinsically robust (e.g., inorganic) materials.

5.
Chem Commun (Camb) ; 56(10): 1541-1544, 2020 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-31922170

RESUMO

We report the application of a Ni-based coordination polymer derived from 1,2,4,5-tetraaminobenzene (P1) as a fast and stable potassium battery anode. In a voltage range of 0.5-2.0 V vs. K+/K, a reversible capacity of 220 mA h g-1 was obtained at 0.1 A g-1. Even with a relatively high electrode loading of 5.0 mg cm-2 and only 10 wt% carbon additive, 118 mA h g-1 was still retained at 1 A g-1. For thinner electrodes with 30 wt% carbon, a capacity of up to 104 mA h g-1 was observed at 10 A g-1 (charging in ∼40 seconds). An areal capacity of up to 2.73 mA h cm-2 was demonstrated. The capacity fade at 1 A g-1 was only 4.4% after 200 cycles. Structure transformations of P1 during charge/discharge were studied using X-ray photoelectron spectroscopy and in situ X-ray diffraction.

6.
J Phys Chem A ; 124(1): 135-140, 2020 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-31820980

RESUMO

Thermal effects in organo-metal halide perovskites are studied by ab initio molecular dynamics (MD) simulations performed at effective temperatures of 293 and 383 K and by X-ray photoelectron spectroscopy (XPS). We find that the cause of thermal instability in this class of perovskites is the rotation of the methylammonium (MA) groups that destroy the rigid lattice of pure compounds (MAPbI3 and MAPbBr3). When the Pb-I lattice is initially distorted by partial replacement of the I with Cl or Br, this not only prevents formation of PbI2 seeds but also improves lattice flexibility and stability against the temperature-induced motion and rotation of MA groups.

7.
J Phys Condens Matter ; 32(9): 095501, 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-31722319

RESUMO

In this study, we investigate the photo-/thermal degradation mechanism of hybrid perovskites by using x-ray photoelectron (XPS) valence band (VB) spectra coupling with density functional theory (DFT) calculations. Herein, CH3NH3PbI3 is respectively subjected to irradiation with visible light and annealing at an exposure of 0-1000 h. It is found from XPS survey spectra that, in both cases (irradiation and annealing), a decrease in the I:Pb ratio is observed with aging time, which unambiguously indicates the formation of PbI2 as the product of photo/thermal degradation. The comparison of the XPS VB spectra of irradiated and annealed perovskites with the DFT calculations of CH3NH3PbI3 and PbI2 compounds have showed a systematic decrease in the contribution of I-5p states, which allows us to determine the respective threshold for degradation, which is 500 h for light irradiation and 200 h for annealing. This discrepancy might be due to the fact that the relaxation of thermal excitations of the system is carried out only by the phonons (which are non-radiative physical processes) while the radiative processes occurred during the photoexcitation will elastically or inelastically divert part of the external energy from the system to reduce its impact on perovskite degradation.

8.
J Phys Chem Lett ; 11(1): 333-339, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31838849

RESUMO

We report the first systematic assessment of intrinsic photothermal stability of a large panel of complex lead halides APbX3 incorporating different univalent cations (A = CH3NH3+, [NH2CHNH2]+, Cs+) and halogen anions (X = Br, I) using a series of analytical techniques such as UV-vis and X-ray photoelectron spectroscopy, X-ray diffraction, EDX analysis, atomic force and scanning electron microscopy, ESR spectroscopy, and mass spectrometry. We show that heat stress and light soaking induce a severe degradation of perovskite films even in the absence of oxygen and moisture. The stability of complex lead halides increases in the order MAPbBr3 < MAPbI3 < FAPbI3 < FAPbBr3 < CsPbI3 < CsPbBr3, thus featuring all-inorganic perovskites as the most promising absorbers for stable perovskite solar cells. An important correlation was found between the stability of the complex lead halides and the volatility of univalent cation halides incorporated in their structure. The established relationship provides useful guidelines for designing new complex metal halides with immensely improved stability.

9.
J Phys Chem Lett ; 10(18): 5440-5445, 2019 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-31495174

RESUMO

Polymeric aromatic amines were shown to be very promising cathodes for lithium-ion batteries. Surprisingly, these materials are scarcely used for designing post-lithium batteries. In this Letter, we investigate the application of the high-voltage poly(N-phenyl-5,10-dihydrophenazine) (p-DPPZ) cathodes for K-ion batteries. The designed batteries demonstrate an impressive specific capacity of 162 mAh g-1 at the current density of 200 mA g-1, operate efficiently at high current densities of 2-10 A g-1, enabling charge and discharge within ∼1-4 min, and deliver the specific capacity of 125-145 mAh g-1 with a retention of 96 and 79% after 100 and 1000 charge-discharge cycles, respectively. Finally, these K-ion batteries with polymeric p-DPPZ cathodes showed rather outstanding specific power of >3 × 104 W kg-1, thus paving a way to the design of ultrafast and durable high-capacity metal-ion batteries matching the increasing demand for high power and high energy density electrochemical energy storage devices.

10.
J Phys Condens Matter ; 31(41): 415301, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31292291

RESUMO

X-ray and optical spectroscopies were applied in order to study the band structure and electronic excitations of the SiO x /R y O z (R = Si, Al, Zr) suboxide superlattices. The complementary x-ray emission and absorption measurements allow for the band gap values for the SiO x layers to be established, which are found to have almost no dependency on the cation type R. It is determined that, after annealing, the stoichiometric factor x remains near 1.8 in all the systems under study, implying that the silicon quantum dot synthesis reaction is not fully completed. It is shown that the SiO x /Al2O3 multilayer contains octahedral structural motifs (SiO6) usually found in stishovite, whereas SiO x /SiO2 and SiO x /ZrO2 demonstrate an electronic structure similar to conventional silica. The intrinsic electronic excited states are examined by means of synchrotron-excited photoluminescence spectroscopy. Low-energy UV-excited luminescence of SiO x layers is found to have the same spectrum in all of the studied structures, while VUV-excited spectra strongly depend on the cation R. In these measurements, manifestations of 'slow' exciton-mediated and 'fast' defect-related luminescence are distinguished using nanosecond time resolution. It is shown that both mobile and bounded excitons appear in the suboxide layer under 6.2 eV and 5.8 eV irradiation and then relax radiatively through the triplet-singlet transition of the neighbouring oxygen-deficient centers. The complete picture of the optical excitation and relaxation processes in these materials is illustrated in a general diagram depicting electronic states.

11.
J Phys Condens Matter ; 29(40): 405804, 2017 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-28857048

RESUMO

We present measurements of resistivity, x-ray absorption (XAS) and emission (XES) spectroscopy together with ab initio band structure calculations for quasi two dimensional ruthenate Na2RuO3. Density function calculations (DFT) and XAS and XES spectra both show that Na2RuO3 is a semiconductor with an activation energy of ∼80 meV. Our DFT calculations reveal large magneto-elastic coupling in Na2RuO3 and predict that the ground state of Na2RuO3 should be antiferromagnetic zig-zag.

12.
Langmuir ; 33(39): 10118-10124, 2017 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-28873309

RESUMO

We demonstrate a facile approach to designing transparent electron-collecting electrodes by depositing thin layers of medium and low work function metals on top of transparent conductive metal oxides (TCOs) such as ITO and FTO. The modified electrodes were fairly stable for months under ambient conditions and maintained their electrical characteristics. XPS spectroscopy data strongly suggested integration of the deposited metal in the TCO structure resulting in additional doping of the conducting oxide at the interface. Kelvin probe microscopy measurements revealed a significant decrease in the ITO work function after modification. Organic solar cells based on three different conjugated polymers have demonstrated state of the art performances in inverted device geometry using Mg- or Yb-modified ITO as electron collecting electrode. The simplicity of the proposed approach and the excellent ambient stability of the modified ITO electrodes allows one to expect their wide utilization in research laboratories and electronic industry.

13.
J Phys Chem Lett ; 8(6): 1211-1218, 2017 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-28220700

RESUMO

We report a careful and systematic study of thermal and photochemical degradation of a series of complex haloplumbates APbX3 (X = I, Br) with hybrid organic (A+ = CH3NH3) and inorganic (A+ = Cs+) cations under anoxic conditions (i.e., without exposure to oxygen and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI3) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the cesium-based all-inorganic complex lead halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks.

14.
J Chem Phys ; 143(22): 224704, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26671393

RESUMO

The electronic structure of [6,6]-phenyl C61 butyric acid methyl ester (PCBM), poly(3-hexylthiophene) (P3HT), and P3HT/PCBM blends is studied using soft X-ray emission and absorption spectroscopy and density functional theory calculations. We find that annealing reduces the HOMO-LUMO gap of P3HT and P3HT/PCBM blends, whereas annealing has little effect on the HOMO-LUMO gap of PCBM. We propose a model connecting torsional disorder in a P3HT polymer to the HOMO-LUMO gap, which suggests that annealing helps to decrease the torsional disorder in the P3HT polymers. Our model is used to predict the characteristic length scales of the flat P3TH polymer segments in P3HT and P3HT/PCBM blends before and after annealing. Our approach may prove useful in characterizing organic photovoltaic devices in situ or even in operando.


Assuntos
Fulerenos/química , Polímeros/química , Teoria Quântica , Tiofenos/química , Elétrons
15.
Sci Rep ; 5: 15380, 2015 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-26486966

RESUMO

This study reports a scalable and economical method to open a band gap in single layer graphene by deposition of cobalt metal on its surface using physical vapor deposition in high vacuum. At low cobalt thickness, clusters form at impurity sites on the graphene without etching or damaging the graphene. When exposed to oxygen at room temperature, oxygen functional groups form in proportion to the cobalt thickness that modify the graphene band structure. Cobalt/Graphene resulting from this treatment can support a band gap of 0.30 eV, while remaining largely undamaged to preserve its structural and electrical properties. A mechanism of cobalt-mediated band opening is proposed as a two-step process starting with charge transfer from metal to graphene, followed by formation of oxides where cobalt has been deposited. Contributions from the formation of both CoO and oxygen functional groups on graphene affect the electronic structure to open a band gap. This study demonstrates that cobalt-mediated oxidation is a viable method to introduce a band gap into graphene at room temperature that could be applicable in electronics applications.


Assuntos
Cobalto/química , Grafite/química , Oxirredução , Catálise , Óxidos/química , Oxigênio/química , Propriedades de Superfície
16.
Mater Sci Eng C Mater Biol Appl ; 42: 529-37, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25063150

RESUMO

The work presents results of the studies performed on electropolishing of pure niobium in a bath that contained: sulphuric acid, hydrofluoric acid, ethylene glycol and acetanilide. After the electropolishing, the specimens were subjected to anodic passivation in a 1moldm(-3) phosphoric acid solution at various voltages. The surface morphology, thickness, roughness and chemical composition of the resulting oxide layers were analysed. Thusly prepared niobium samples were additionally investigated in terms of their corrosion resistance in Ringer's solution. The electropolished niobium surface was determined to be smooth and lustrous. The anodisation led to the growth of barrier-like oxide layers, which were enriched in phosphorus species.


Assuntos
Corrosão , Técnicas Eletroquímicas , Nióbio/química , Oxirredução , Ácidos Fosfóricos , Espectroscopia Fotoeletrônica , Propriedades de Superfície
17.
Adv Mater ; 26(28): 4870-4, 2014 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-24903059

RESUMO

The first 4 eV of the conduction band in graphene oxide is dominated by states from carbon sites that are in close proximity, but not directly bonded, to oxidizing functional groups. The carbon sites that are bonded directly to these groups, such as epoxide and hydroxyl groups, are much higher in energy.

18.
Mater Sci Eng C Mater Biol Appl ; 39: 259-72, 2014 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-24863224

RESUMO

This paper reports on the surface modification of a Ti-15Mo alloy by plasma electrolytic oxidation (PEO). This process was carried out in solutions of 0.1M Ca(H2PO2)2 with various concentrations of tricalcium phosphate (Ca3(PO4)2), wollastonite (CaSiO3), or silica (SiO2) using voltages of up to 350V. The surface microstructure (SEM, cross-section of coating), roughness and chemical composition (energy-dispersive X-ray spectroscopy, thin layer X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy) of the porous oxide layers were investigated. The concentration of powder added to the solution changed the chemical composition and morphology of PEO coatings on the Ti-15Mo alloy surface. Calcium and phosphorous compounds were detected in the coatings formed on the substrate by the PEO process at 300V.


Assuntos
Ligas/química , Eletrólise/métodos , Oxirredução , Fosfatos de Cálcio/química , Materiais Revestidos Biocompatíveis/química , Teste de Materiais/métodos , Espectroscopia Fotoeletrônica , Porosidade , Dióxido de Silício/química , Espectrometria por Raios X , Propriedades de Superfície , Suspensões , Difração de Raios X
19.
Chemistry ; 18(10): 2912-22, 2012 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-22290810

RESUMO

We demonstrate that the electronic structure of mesoporous silicon is affected by adsorption of nitro-based explosive molecules in a compound-selective manner. This selective response is demonstrated by probing the adsorption of two nitro-based molecular explosives (trinitrotoluene and cyclotrimethylenetrinitramine) and a nonexplosive nitro-based aromatic molecule (nitrotoluene) on mesoporous silicon using soft X-ray spectroscopy. The Si atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as evident from the large shifts in emission energy present in the Si L(2,3) X-ray emission spectroscopy (XES) measurements. Furthermore, we find that the energy gap (band gap) of mesoporous silicon changes depending on the adsorbant, as estimated from the Si L(2,3) XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab initio molecular dynamics calculations of model compounds suggest that these changes are due to spontaneous breaking of the nitro groups upon contacting surface Si atoms. This compound-selective change in electronic structure may provide a powerful tool for the detection and identification of trace quantities of airborne explosive molecules.

20.
Anal Sci ; 21(7): 811-3, 2005 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-16038501

RESUMO

A numerical simulation was done to check the possibility of using planar C/C/C multilayers with density contrast 0.2 and 0.7 g/cm3 as an X-ray waveguide. After an optimization procedure, suitable waveguide layer thicknesses were found which provide a high degree of resonant standing wave field intensity enhancement in the core layer at incident beam energy of 13 keV. The obtained results were compared with those of the Mo/Be/Mo waveguide, whose high waveguiding capability at the same energy value was reported in the 1990s. The comparison shows that standing wave field intensity resonant enhancement provided by C/C/C planar multilayers is very high and, consequently, a guided beam can be well detected.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...