Search results for " semiconductor"
showing 10 items of 332 documents
Photocurrent spectroscopy in passivity studies
2018
The aim of this article is to present photocurrent spectroscopy as useful in situ technique for the physicochemical characterization of passive films and corrosion layers. The response of (both amorphous and crystalline) semiconductor/electrolyte junction under irradiation is treated and discussed in order to get information about solid-state properties such as band gap and flat band potential. The possibility to use Photocurrent Spectroscopy (PCS), in a quantitative way, to get information on the composition of corrosion layers is discussed through a semiempirical correlation between the band gap of the oxides (or hydroxides) and the difference of electronegativity of their constituents. F…
Efficient wide band gap double cation – double halide perovskite solar cells
2017
In this work we study the band gap variation and properties of the perovskite compound Cs0.15FA0.85Pb(BrxI1−x)3 as a function of the halide composition, with the aim of developing an efficient complementary absorber for MAPbI3 in all-perovskite tandem devices. We have found the perovskite stoichiometry Cs0.15FA0.85Pb(Br0.7I0.3)3 to be a promising candidate, thanks to its band gap of approximately 2 eV. Single junction devices using this perovskite absorber lead to a maximum PCE of 11.5%, among the highest reported for solar cells using perovskites with a band gap wider than 1.8 eV.
Optical and magnetic properties of ZnCoO thin films synthesized by electrodeposition
2008
Ternary Zn1−xCoxO crystalline films with different compositions were grown by electrodeposition. The Co content in the final compound is linked to the initial Co/Zn ratio in the starting solution. X-ray diffraction reveals a wurtzite structure for the Zn1−xCoxO films. Transmittance spectra show two effects proportional to Co content, a redshift of the absorption edge and three absorption bands, which are both interpreted to be due to the Co incorporated into the ZnO lattice. The amount of deposited charge was used to get a precise control of the film thickness. Magnetic measurements point out that Co(II) ions are isolated from each other, and consequently the films are paramagnetic. Francis…
Spin polarized tunneling at room temperature in a Heusler compound-a non-oxide material with a large negative magnetoresistance effect in low magneti…
2003
Summary form only given. Materials which display large changes in resistivity in response to an applied magnetic field (magnetoresistance) are currently of great interest due to their potential for applications in magnetic sensors, magnetic random access memories, and spintronics-a new kind of electronics based on spin instead of charge. Although ferromagnetic manganites show colossal magnetoresistance (CMR) effects around their Curie temperature, the low field and nearly temperature independent magnetoresistance properties important for spintronics are found only at low temperatures. Guided by striking features in the electronic structure of several magnetic compounds, we prepared the Heus…
Assessment on the use of the amorphous semiconductor theory for the analysis of oxide films
2015
Abstract Although the theory of Schottky barrier in amorphous semiconductors is generally accepted, the limits of validity of such theory have not yet been explored. The classic semi-analytical solution is obtained under the constraint of constant electronic density of states (DOS) distribution in the mobility gap. In order to take into account the presence of a DOS variable in energy, a semi-empirical corrective power law was introduced in this paper. It is shown that the equations derived for thick films maintain their validity also in the case of thin films, provided that the space charge region width remains lower than 70% of the whole film thickness. A new expression based on the use o…
Surface band-gap narrowing in quantized electron accumulation layers.
2010
An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.
PEDOT thin films with n-type thermopower
2019
peer-reviewed Synthesis of n-type organic semiconductors is challenging as reduced states are difficult to obtain due to their instability in air. Here, we report tailoring of semiconducting behavior through control of surfactant concentration during synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles. Nanoparticles were synthesized by mini-emulsion polymerization, where stable suspensions were used to produce polymer films by a simple casting technique on polyethylene terephthalate (PET) substrates. Electrical conductivity and Seebeck coefficients were measured as a function of surfactant concentration. It was found that conductivity decreases three orders of magnitude as s…
Phosphomolybdic acid as an efficient hole injection material in perovskite optoelectronic devices.
2018
Efficient perovskite devices consist in a perovskite film sandwiched in between charge selective layers, in order to avoid non-radiative recombination. A common metal oxide used as p-type or hole transport layer is molybdenum oxide. MoO3 is of particular interest for its very large work function, which allows it to be used both as an interfacial charge transfer material as well as a dopant for organic semiconductors. However, high quality and high work function MoO3 is typically thermally evaporated in vacuum. An alternative solution-processable high work function material is phosphomolybdic acid (PMA), which is stable, commercially available and environmentally friendly. In this communicat…
Quantum chemical simulations of doped ZnO nanowires for photocatalytic hydrogen generation
2016
Zinc oxide (ZnO) is considered in general as a promising material for solar water splitting. Its wurtzite-structured bulk samples, however, can be considered as active for photocatalytic applications only under UV irradiation, where they possess ∼1% efficiency of sunlight energy conversion due to their wide band gap (3.4 eV). Although pristine ZnO nanowires (NWs) possess noticeably narrower band gaps than the bulk, the tendency of band gap reduction with increasing NW diameter is insufficient, and further modification is required. We have contributed to filling this gap by performing a series of ab initio calculations on ZnO NWs of different diameters (dNW), which are mono-doped by metal (A…
Doped semiconductors as half-metallic materials: Experiments and first-principles calculations ofCoTi1−xMxSb(M=Sc, V, Cr, Mn, Fe)
2008
This work reports experiments and first-principles calculations on the substitutional semiconducting $C{1}_{b}$ compound $\mathrm{Co}{\mathrm{Ti}}_{1\ensuremath{-}x}{M}_{x}\mathrm{Sb}$. Diluted magnetic semiconductors have been prepared by substituting titanium in the semiconducting compound CoTiSb by other $3d$ transition elements $M$. Self-consistent calculations of the electronic structure predict some of the materials to be half-metallic ferromagnets. The structural, electronic, electric, and magnetic properties of the pure and substituted materials have been investigated. It is found from the experiments that substitution of up to 10% Ti by Fe, Mn, Cr, and V does not affect the crystal…