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The Coach6 software and the CoachLabII+ measuring console coupled with a computer and equipped with appropriate voltage and current sensors were used to determine the current-voltage and power-voltage characteristics of the photovoltaic cells. The current-voltage and power-voltage characteristics for a single cell and cells connected in series and in parallel were tested depending on the light intensity. Using a simplified theoretical model of a photovoltaic cell based on the one-diode equivalent circuit and Shockley diode equation, the ideality factor, diode saturation current and source current were determined, fitting the appropriate theoretical relationship to the measurement results. Based on the current-voltage and power-voltage characteristics, the short-circuit current, open circuit voltage, maximum power, fill factor, conversion efficiency and load resistance were determined. The dependence of the determined parameters on the light intensity was discussed.

The volume filling fraction dependence of the effective permittivity of the nematic liquid crystal 4-n-pentyl-4’-cyanobiphenyl embedded in different porous membranes and dispersed with aerosil nano...

Dielectric spectroscopy in the frequency range from 10−2 to 107 Hz was applied to investigate the dynamics of the relaxation processes in a banana-shaped liquid crystal compound with fluorinated ch...

The article presents the basic properties of liquid crystals with particular emphasis on their use in the construction of liquid crystal displays. The basic properties of liquid crystal displays, their structure and principle of operation are discussed. The selected examples show the benefits of using liquid crystal displays in vehicle transportation and aviation.

Broadband dielectric spectroscopy was applied to investigate the effect of gel-former agent on the dynamics of the collective modes in a ferroelectric liquid crystal mixture. In the investigated range of gel concentrations, the dynamics of the Goldstone mode is significantly reduced due to the formation of a hydrogen bonding network of the gel-former agent in ferroelectric liquid crystal. The observed changes in dynamics of the collective processes are sensitive to the history of the thermal treatment of the samples.

The effect of hydrophobic aerosil nanoparticles on the dynamics of the soft mode and the Goldstone mode near the SmA*–SmC* phase transition in the ferroelectric liquid crystal (S)-2-methylbutyl 4-n-nonanoyloxybiphenyl-4′-carboxylate has been investigated by means of broadband dielectric spectroscopy. The obtained results for hydrophobic aerosil composites exhibit some differences in the dynamics of the collective processes as compared with dielectric measurements for hydrophilic aerosil dispersions. The observed changes in dynamics of the collective modes near the SmA*–SmC* phase transition were explained taking into account differences in surface treatment of the aerosil nanoparticles and effect of random disorder.

In the cylindrical pore geometry of inorganic Anopore membranes the collective relaxation processes observed in a bulk antiferroelectric liquid crystal change considerably under confinement. The frequency degeneration of the soft and Goldstone modes present at the smectic A* (SmA*)–chiral smectic C (SmC*) phase transition in the bulk phase is removed under geometrical restrictions. The relaxation rate of the soft mode is strongly modified due to the deformation of the smectic layers in the curved geometry of the pores and is superimposed by the molecular relaxation process in the SmA* and SmC* phases. The soft mode in confinement splits into two relaxation processes, which are present through all other mesophases (SmC* and SmCa*). One of them is nearly temperature independent and slightly decreases in frequency in the SmCa* phase. This Goldstone‐like process can be assigned to the highly deformed helical structure fluctuations. The second one exhibits the characteristic features for the molecular and soft...

Broadband dielectric spectroscopy was applied to investigate a newly synthesized antiferroelectric liquid crystal, (S)‐(+)‐4′‐(1‐methylheptyloxycarbonyl)biphenyl‐4‐yl 4‐(6‐heptanoyloxyhex‐1‐oxy)benzoate. Near the SmA–SmC* phase transition the soft and the Goldstone modes are observed. The temperature dependence of the soft mode dielectric strength follows the Cure–Weiss law. In a narrow range of temperature the collective and antiferroelectric relaxation modes coexist as a result of the competition between ferroelectric and antiferroelectric order in the successive smectic layers. In the antiferroelectric phase the low frequency, PL, and high frequency, PH, modes appear, which can be related to the in‐phase and anti‐phase azimuthal angle fluctuations of the director, respectively. The relaxation frequency of the PH and PL modes decreases linearly with decreasing temperature and satisfies the Arrhenius law. Some parameters involved in the extended Landau model of the SmA–SmC* phase transition could be obta...

On the basis of the extended Landau mean field model for the SmA—SmC* phase transition the temperature dependence of the dielectric strength and of the characteristic relaxation frequency of the soft mode are analyzed and some parameters involved in the free energy expansion are determined. The analogies and differences between the influence of the aerosil density and a dc electric field are shown.

Collective relaxation processes are completely undetectable in a ferroelectric liquid crystal confined in porous Anopore membranes, as a result of perfect orientation of the smectic layers perpendicular both to the long axis of the pores and the direction of the measuring electric field. In the ferroelectric liquid crystal – Anopore composite only one relaxation process, assigned to rotation of the molecule around the molecular short axis, appears throughout all smectic phases. The temperature dependence of the relaxation frequency and of the dielectric strength of this process also shows no irregularity at the point of polarization sign reversal. The temperature dependence of the relaxation frequency follows the Arrhenius law with an activation energy slightly higher in the ferroelectric SmC* phase. Analysis of the non‐linear changes of temperature dependence of the dielectric strength at the SmA–SmC* phase transition enables one to obtain the temperature dependence of the tilt angle of the molecules in ...

Dielectric spectroscopy was used to study the influence of random disorder in aerosil–ferroelectric liquid crystal dispersions on the dynamics of the Goldstone mode near the point of polarization sign reversal and the relaxation rate and dielectric strength of the collective modes. In general, the dielectric strength and the relaxation frequency of the Goldstone mode decrease, in comparison with the bulk, with increasing aerosil density near a point of polarization sign reversal. However, the characteristic frequency of the Goldstone mode varies with silica density in an opposite manner on each side of this point. This can be explained as a different sensitivity on the spatial confinement of different molecular conformers above and below the point of polarization sign reversal. The experimental results of temperature and frequency dependence of the complex dielectric constant are compared with predictions of the generalized Landau model for ferroelectric liquid crystals.

Broadband dielectric spectroscopy was applied to study the influence of the dispersed hydrophilic aerosil particle densities on the second-order smectic-A–smectic-C* phase transition and polarization sign reversal in the ferroelectric liquid crystal S-(−)-2-methylbutyl 4- n -nonanoyloxybiphenyl-4′-carboxylate. With increasing aerosil concentration the dielectric strength of the soft and the Goldstone mode considerably decreases and the complete disappearance of the Goldstone mode at ρ s = 0.20 g/cm 3 occurs along with significant broadening of the soft mode. The characteristic frequency of the Goldstone mode slightly increases with increasing density of the silica particles. The frequency degeneracy taking place in the smectic-A–smectic-C* phase transition is removed in the presence of aerosil and an increase in the frequency gap is observed. In a point of polarization sign reversal a rapid drop of the dielectric strength and the disappearance of the Goldstone mode was detected for bulk and confined ferroelectric liquid crystal. However, with increasing concentration of aerosil particles the dielectric strength of the Goldstone mode decreases as a function of temperature stronger below than above the sign reversal point. The characteristic frequency of the Goldstone mode below the point of polarization sign reversal decreases with increasing aerosil concentration.

The influence of the concentration of hydrophilic aerosil particles on the collective dynamic modes of the ferroelectric liquid crystal S‐(‐)‐2‐methylbutyl 4‐n‐nonanoyloxybiphenyl‐4′‐carboxylate near the SmA–SmC* phase transition is investigated by means of dielectric spectroscopy in the frequency range 10−2–107 Hz. For aerosil densities ρs = 0.025, 0.05, 0.08 and 0.15 g cm−3 considerable changes in the dielectric intensities of Goldstone and soft modes are observed. The characteristic frequency of the Goldstone mode slightly increases with increasing concentration of aerosil. The frequency degeneracy occurring in the SmA–SmC* phase transition is lifted in the presence of aerosil and an increase in the frequency gap is observed. Complete disappearance of the Goldstone mode at ρs = 0.20 g cm−3 occurs, along with significant broadening of the soft mode. The results are interpreted as an effect of structure, surface interactions and length scale of the helix in disordered confinement.

Real-time dielectric relaxation spectroscopy for a molecular beam deposited glass forming liquids is proposed as a versatile approach for the study of the dynamic glass transition in geometric confinement. To achieve the highest sensitivity down to monomolecular organic layers in a wide frequency range (0.1 - 10^7 Hz) during simultaneous deposition and desorption, we have used μm spaced interdigitated electrodes under ultrahigh vacuum conditions. Experiments using glycerol deposited on fused silica at -40◦C revealed a dielectric glass transition process for a layer thickness as low as 0.7 nm. While its peak position hardly changes upon thickness reduction, a clear broadening of the relaxation peak is observed that implies an increasing heterogeneous mobility scenario for the thinnest films caused by molecules being part of a reduced (at the substrate) or enhanced (free surface) mobility layer. This finding is supported by desorption experiments that reveal a strong retardation of the desorption rate for films below 1 nm. ispartof: European Physical Journal. Special Topics vol:189 issue:1 pages:181-186 ispartof: location:Grenoble status: published