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Shallow Traps (shallow + trap)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Electron Trapping in Higher Adduct Fullerene-Based Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Martijn Lenes
Abstract Here, the performance of bulk-heterojunction solar cells based on a series of bisadduct analogues of commonly used derivatives of C60 and C70, such PCBMs and their thienyl versions, is investigated. Due to their higher lowest unoccupied molecular orbital an increase in open-circuit voltage and thus performance is expected. It is shown that the occurrence of a multitude of different isomers results in a decrease in the electron transport for some of the materials. Surprisingly, the solar-cell characteristics are very similar for all materials. This apparent discrepancy is explained by a significant amount of shallow trapping occurring in the fullerene phase that does not hamper the solar cell performance due the filling of these shallow traps during illumination. Furthermore, the trisadduct analogue of [60]PCBM has been investigated, which, despite an even further increase in open-circuit voltage, results in a significantly reduced device performance due to a strong deterioration of the electron mobility in the fullerene phase. [source]

Afterglow and thermally stimulated luminescence induced by UV radiation in CVD diamond

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2007
M. Barboza-Flores
Abstract Afterglow (AG) and thermoluminescence (TL) of CVD diamond UV-irradiated with wavelength of 200,260 nm at room temperature are reported. The AG curves monotonously decrease with time and are fitted well by the hyperbolic law. The decay times depends on UV wavelength and decreases with the AG intensity increasing. The TL glow curves exhibit two pronounced TL peaks with maxima at about 350 K and 513 K with unstructured signal between them and are fitted well by four TL peaks. The first, 350 K peak with the activation energy of 0.59 eV was supposed to be second kinetics order. The higher temperature peaks at 402 K, 445 K and 513 K with the activation energies of 0.46 eV, 0.49 eV and 0.68 eV, respectively were assumed to be first kinetics order. The comparison of the AG decay times with the kinetics parameters of the 350 K TL peak proved that AG is caused by thermal emptying of the traps responsible for the 350 K peak. The behaviour of AG and 350 K TL peak was described by the model, in which shallow traps, recombination centers and deep thermally disconnected traps are taken into account. The AG and TL creation spectra are practically the same and consists of a broad band, which exponentially increases from 260 nm, reaches a maximum at 240 nm and then begins decreasing. The creation spectra of the AG and TL peaks are the same and closely related with the fundamental absorption of UV light near indirect band gap of diamond. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Atomic structure and positron lifetime in the metallic glass Zr55Cu30Ni5Al10

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
K. Sugita
Abstract Zr-based metallic glasses have superior characteristics such as mechanical strength, corrosion resistance and precision casting ability. From positron lifetime measurements, a negative temperature dependence of the mean positron lifetime above room temperature was reported and ascribed to the presence of shallow traps. However, the trapping sites remain unknown under the present circumstances. To get a further understanding of the experimental positron lifetime value, the positron density distribution and the lifetime in the Zr-based metallic glass Zr55Cu30Ni5Al10 have been calculated. The calculation shows that the positrons are annihilated inhomogeneously and most positrons are annihilated preferentially around Cu/Al. These results indicate that the positron lifetime not exactly reflects the total free volume. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ionic and electronic defects in a-BaTiO3 thin films studied by transient and steady state conductivity measurements

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
F. El Kamel
Abstract Conduction mechanisms in BaTiO3 films deposited at low temperatures on Cu-electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J - E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 1022 m,3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]