The photoconductivity in thin films of a new composite based on CdSe nanoplatelets (NPL) and PCDTBT polymer has been studied using photoconductivity spectrum, I-U and lux-ampere measurements at various temperatures. The incorporation of 7 vol.% of NPLs into the polymer blend led to an increase in photoconductivity by an order of magnitude compared to the pristine PCDTBT film in the temperature range of 310–360 K and the electric field strength above 200 V cm –1 . An analysis of current-voltage and luminous characteristics measured at various temperatures demonstrated that the observed increase in the photoconductivity of the composite is due to a change in the transport mechanism of nonequilibrium charge carriers with an increase in their concentration. The observed saturation of photoconductivity with increasing temperature is supposed to occur due to the increase in exciton diffusion length with temperature increasing and limited exciton generation area.

One-dimensional periodic surface structures were formed by femtosecond laser irradiation of amorphous hydrogenated silicon (a-Si:H) films. The a-Si:H laser processing conditions influence on the periodic relief formation as well as correlation of irradiated surfaces structural properties with their electrophysical properties were investigated. The surface structures with the period of 0.88 and 1.12 μm were fabricated at the laser wavelength of 1.25 μm and laser pulse number of 30 and 750, respectively. The orientation of the surface structure is defined by the laser polarization and depends on the concentration of nonequilibrium carriers excited by the femtosecond laser pulses in the near-surface region of the film, which affects a mode of the excited surface electromagnetic wave which is responsible for the periodic relief formation. Femtosecond laser irradiation increases the a-Si:H films conductivity by 3 to 4 orders of magnitude, up to 1.2 × 10−5 S∙cm, due to formation of Si nanocrystalline phase with the volume fraction from 17 to 28%. Dark conductivity and photoconductivity anisotropy, observed in the irradiated a-Si:H films is explained by a depolarizing effect inside periodic microscale relief, nonuniform crystalline Si phase distribution, as well as different carrier mobility and lifetime in plane of the studied samples along and perpendicular to the laser-induced periodic surface structures orientation, that was confirmed by the measured photoconductivity and absorption coefficient spectra.

The effect of the annealing of CH3NH3PbI3 perovskite on its electrical, photoelectric and optical properties has been estimated. The annealing leads to a two-phase structure consisting of perovskite and lead iodide, whose relative concentrations depend on the annealing temperature. The formation of a PbI2 phase in a perovskite film upon heating leads to a decrease in the conductivity and photoconductivity of two-phase material, which contradicts the assumption of a decrease in recombination associated with PbI2, obtained by measuring the parameters of a solar cell.

Amorphous silicon films were modified by femtosecond laser pulses. Revealed on irradiated surface are micron-scale laser-induced periodic structures that affect anisotropy of dark conductivity, photoconductivity and carrier mobility within the film.

An approach for the determination of the distribution of density of electronic states in organic photoconductors is proposed. It is based on the analysis of absorption coefficient spectral dependence and the photoconductivity temperature dependence of photosensitive thin solid films. Feasibility of the approach is demonstrated by a study of the dependences using co-polymer of phenylquinoline derivative and 2,1,3-benzothiadiazole as an organic photoconductor. The distributions of density of electronic states are described well by the Gaussian function, and the corresponding full-width at-half-maxima are determined.

The effect of annealing of organometallic perovskite CH3NH3PbI3 film on its electrical, photoelectric, and optical properties is studied. It was shown that annealing at Та>140 °C leads to the two-phase structure formation consisting of perovskite and lead iodide, the relative content of which depends on the annealing conditions, in particular, on its temperature. The PbI2 formation in the perovskite structure leads to a decrease in the conductivity and photoconductivity of the material. Our studies indicate the possibility of forming planar structures consisting of semiconductor materials with various values of the band gap: 1.6 eV (CH3NH3PbI3) and 2.4 eV (PbI2).

The effect of annealing of a CH3NH3PbI3 organometallic perovskite film on its electrical, photoelectrical, and optical properties is studied. It is shown that annealing at the temperature Ta > 140°C results in the formation of a two-phase structure consisting of perovskite and lead iodide, whose relative content depends on the conditions of annealing, specifically, on the annealing temperature. The formation of PbI2 in the perovskite structure yields a decrease in the conductivity and photoconductivity of the material. The studies suggest the possibility of the formation of planar structures composed of semiconductor materials with different band gaps, 1.6 eV (CH3NH3PbI3) and 2.4 eV (PbI2).

Abstract A significant effect of the environment (vacuum, air) on the results of measurements of CH3NH3PbI3 films conductivity and photoconductivity is shown. It was found that prolonged illumination with white light does not change the value of CH3NH3PbI3 interband photoconductivity (hν > 1.6 eV), but leads to a metastable increase in the photoconductivity near the quantum energy hν ≈ 1.2 eV. This indicates a photoinduced creation or filling of nonrecombination localized states, located at an energy distance of 1.2 eV from the transport level of nonequilibrium charge carriers.

Anisotropic periodic relief in form of ripples was formed on surface of amorphous hydrogenated silicon (a-Si:H) films by femtosecond laser pulses with the wavelength of 1.25 μm. The orientation of the surface structures relative to laser radiation polarization vector depended on the number of laser pulses N acting on the film surface. When N = 30, the structures with 0.88 μm period were formed orthogonal to the laser radiation polarization; at N = 750 the surface structures had period of 1.12 μm and direction parallel to the polarization. The conductivity of the laser-modified a-Si:H films increased by 3 to 4 orders of magnitude, up to 3.8·10–5 (Ω∙cm)–1, due to formation of nanocrystalline Si phase with a volume fraction from 17 to 30%. Anisotropy of the dark conductivity, as well as anisotropy of the photoconductivity spectral dependences was observed in the modified films due to depolarizing influence of periodic microscale relief and uneven distribution of nanocrystalline Si phase within such laser-induced structure.

It is known that the photovoltaic properties of organic perovskite based solar cells decline at high humidity that is one of the perovskite solar cells disadvantages. We investigated the effect of humidity on the perovskite CH(3)NH(3)PbI(3)conductivity that can be applied to creation of cheap and effective humidity sensors. The measurements have shown that perovskite CH(3)NH(3)PbI(3)has a competitively high sensitivity to humidity. The mechanisms that lead to a change in the perovskite conductivity in a humid environment are proposed.

Electrical, photoelectrical, and optical properties of thin films of a new heat-resistant polyphenylquinoline synthesized using facile methods were investigated. An analysis of the obtained temperature dependences of the dark conductivity and photoconductivity indicates the hopping mechanism of conductivity over localized states arranging at the energy distance of 0.8 eV from the Fermi level located inside the band gap of the investigated material. The optical band gap of the studied material was estimated from an analysis of the spectral dependences of the photoconductivity and absorption coefficient before (1.8-1.9 eV) and after (2.0-2.2 eV) annealing at temperatures exceeding 100 °C. The Gaussian character of the distribution of the localized states of density inside the band gap near the edges of the bands was established. A mechanism of changes in the optical band gap of the investigating polymer under its annealing is proposed.

The effect of temperature on the photoconductivity and its spectral dependence for thin films of organometallic CH3NH3PbI3 perovskite is studied. The measurements performed at temperatures below room temperature reveal the features of the change in the photoconductivity with temperature in the region of the phase transition from the tetragonal to orthorhombic structure (140–170 K). On the basis of analysis of the effect of temperature on the nature of the change in the spectral dependences of the photoconductivity in the phase-transition region, mechanisms are proposed, which clarify the observed change in the photoconductivity.

In this work, the effect of temperature on photoconductivity and its spectral dependence for thin films of metal-organic perovskite CH3NH3PbI3 was studied. Measurements carried out in the temperature region below room temperature revealed specific features of photoconductivity variation with temperature in the phase transition region from the tetragonal to orthorhombic structure (140–170 K). Based on the analysis of the effect of temperature on the spectral dependences of photoconductivity in the region of the phase transition mechanisms are proposed that determine the observed change in photoconductivity

A one-dimensional surface relief with a 1.20 +/- 0.02 mu m period was formed in amorphous hydrogenated silicon films as a result of irradiation by femtosecond laser pulses (1.25 mu m) with a fluence of 0.15 J cm(-2). Orientation of the formed structures was determined by the polarization vector of the radiation and the number of acting pulses. Nanocrystalline silicon phases with volume fractions from 40 to 67% were detected in the irradiated films according to the analysis of Raman spectra. Observed micro-and nanostructuring processes were caused by surface plasmon-polariton excitation and near-surface region nanocrystallization, respectively, in the high-intensity femtosecond laser field. Furthermore, the formation of Si-III and Si-XII silicon polymorphous modifications was observed after laser treatment with a large exposure dose. The conductivity of the film increased by three orders of magnitude at proper conditions after femtosecond laser nanocrystallization compared to the conductivity of the untreated amorphous surface. The conductivity anisotropy of the irradiated regions was also observed due to the depolarizing contribution of the surface structure, and the non-uniform intensity distribution in the cross-section of the laser beam used for modification.

The modification of boron-doped amorphous hydrogenated silicon films [a-Si:H(B)] with femtosecond laser radiation is studied in this work. It is demonstrated that femtosecond laser crystallization of the a-Si:H(B) film area leads to extremely high values of the free charge carrier (hole) concentration, which is typical for degenerated semiconductors. The free charge carrier concentration is locally determined by measuring the Raman spectra in the modified areas. The shape of Raman spectra is typical for Fano resonance. It is found that the charge carrier concentration in the modified areas may exceed 1020 cm−3 depending on the femtosecond irradiation conditions. The areas with such a high concentration of free charge carriers are also characterized by high volume fraction of crystalline phase (more than 90%). Such a sharp increase in the free charge carrier concentration in the modified areas may be explained by an increase in concentration of electrically active boron atoms. The activation energy of the temperature dependence of the conductivity for laser beam treated areas is in full agreement with the data obtained from the analysis of the Raman scattering spectra.

Direct-write femtosecond laser nano-structuring of 300 nanometer thick a-Si:H films results in space-variant functional metasurfaces with form bire-fringence of up to Delta n approximate to -0.5. Engineering the orientation of local optical axis allows implementing continuous phase profiles of nearly any optical element including arrays of polarization micro-converters and microlenses, polarization gratings, and computer-generated holograms with continuous phase gradients of approximate to 1 rad mu m(-1).

Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures are different, which allows us to orient them relative to each other in a desirable way. Both structures independently influence the optical properties of the modified films, which causes the diffraction of transmitted light and making the films polarization-sensitive. The conductivity of the modified films correlates with the mutual orientation of the anisotropic structures, whereas no interrelation between the photoconductivity and optical performance of the modified films has been observed.

In this work, we present new results on the plasma processing and structure of hydrogenated polymorphous silicon (pm-Si:H) thin films. pm-Si:H thin films consist of a low volume fraction of silicon nanocrystals embedded in a silicon matrix with medium range order, and they possess this morphology as a significant contribution to their growth comes from the impact on the substrate of silicon clusters and nanocrystals synthesized in the plasma. Quadrupole mass spectrometry, ion flux measurements, and material characterization by transmission electron microscopy (TEM) and atomic force microscopy all provide insight on the contribution to the growth by silicon nanocrystals during PECVD deposition. In particular, cross-section TEM measurements show for the first time that the silicon nanocrystals are uniformly distributed across the thickness of the pm-Si:H film. Moreover, parametric studies indicate that the best pm-Si:H material is obtained at the conditions after the transition between a pristine plasma and one containing nanocrystals, namely a total gas pressure around 2 Torr and a silane to hydrogen ratio between 0.05 to 0.1. From a practical point of view these conditions also correspond to the highest deposition rate achievable for a given RF power and silane flow rate.

Поступило в Редакцию 22 июня 2016 г