Application of a polymer nanocomposite with carbon filler to limit overvoltages in a photovoltaic element

The ability of a structure in the form of a photovoltaic element with a built-in posistor layer based on a polymer nanocomposite with carbon filler being in direct thermal contact to protect against overvoltages was studied experimentally and by simulation.It was shown that the current and voltage on the reverse-biased p-n junction of the photovoltaic layer are limited and decrease from the moment when the temperature of this structure reaches values close to the tripping temperature of the posistor nano-composite to the low-conductivity state.The temperature of the photovoltaic layer has a value close to the tripping temperature of the posistor layer,which is equal to~125°C.The possibility of realizing protection against reverse electrical overvoltages and thermal breakdown of photovoltaic systems based on photovoltaic elements with built-in layers of posistor polymer nano-composites with carbon fillers was established.

High-frequency capacitance-voltage characteristics of the heterogeneous structure based on the model of spherical semiconductor particles in a dielectric

The dependence of the parameters of the capacitance effect in heterogeneous dispersed two-component structures based on semiconductors from the bulk fraction of the semiconductor component is modeled.The used method for determining the changes of the energy bands bending on the surface of the spherical semiconductor particle by applying dc electric field allowed to calculate the changes of the dipole moment and effective(taking into account the polarization of the free charge)dielectric constant of this semiconductor particle.This result allowed to use the known models of the dielectric constant of two-component structures for the description of the capacitance field effect in the heterogeneous structures.The relations allowing to estimate the value of the bulk donor concentration in the semiconductor component of the matrix of the heterogeneous system and the statistical mixture have been obtained.The approbation of the obtained calculation relations to evaluate the donor concentration in the ZnO grains of zinc oxide varistor ceramics leads to the correct values that are consistent with estimates of other methods and models.It is established that the sensitivity of the relative dielectric constant to the applied dc electric field is dependent on the bulk fraction of the semiconductor particles in the heterogeneous structures.The bulk fraction of the semiconductor particles significantly affects on the dielectric constant beginning with the values from
0:8 for matrix systems and
0:33 for statistical mixtures.

Percolation effects in dc degradation of ZnO varistors

For quantitative estimation of the degree of electrical disorder(electrical inhomogeneity)in ZnO varistor ceramics caused by a variation in the barrier height at different grain boundaries in a sample,the comparison of threshold electric fields(onsets of highly nonlinear current-voltage characteristics)in ceramics and single grain boundary(GB)is suggested and approved.At dc degradation similar behavior of the current-voltage characteristics of ZnO varistor ceramics and single GB is observed.The percolation model of Shklovskii-De Gennes is applicable for the description of a disorder in ZnO varistor ceramics.The degree of the disorder in ZnO varistor ceramics is not dependent on the duration of dc degradation at least at degradation time below 60 h.At voltages close to the onset of a highly nonlinear region of current-voltage characteristic the correlation radius of infinite cluster is~5 times greater than the average grain size.

Percolation effects in the capacitive properties of metal-oxide varistors in the range of high voltage

C-V characteristics of ZnO-based ceramic structures used in manufacturing high-voltage and low-voltage varistors of different chemical compositions and manufacturing techniques have been investigated.A correlation between the intensity of electric field corresponding to transition of the C-V characteristics to the negative capacitances and average sizes of grains of a varistor structure has been established.Obtained data have been interpreted with the use of notions of the percolation theory of electric conductivity.The Shklovskii-De Gennes model has been used.It has been shown that on the highly nonlinear segment of C-V characteristics of a varistor structure,the size of an infinite cluster are limited to several intercrystallite potential barriers.This result is observed in all kinds of investigated varistor ceramics.

Electrical properties of structures based on varistor ceramics and polymer nanocomposites with carbon filler

The characteristics of a two-layer structure on the basis of the layers of varistor ceramics and polymeric PPTC nanocomposite being in thermal contact for the purpose of using it as a limiter of constant voltage and long-term varying electrical overvoltages are analyzed.A theoretical model of such a structure has been developed,and its main electrical characteristics are simulated.It is shown that the provision of the required output voltage limitation is performed by selecting the classification voltage of the varistor layer.The maximum current of the varistor layer required for heating the structure is determined by the intensity of heat transfer to the environment.It has established a satisfactory agreement between the theoretical and experimental electrical characteristics for the structure based on the layers used in commercial varistors and PPTC fuses.

Isothermal depolarization current in metal-oxide varistor ceramics under various polarizing fields

A method of analysis of experimental kinetic dependences of isothermal depolarization currents in metal-oxide varistor ceramics composed of ZnO–Bi_(2)O_(3)–CoO–Sb_(2)O_(3)–SnO_(2)–MnO–B_(2)O_(3) has been proposed and tested.The method is based on reconstruction of dependences with the use of the Kohlrausch–Williams–Watt function.Expansion of the distribution and reduction of the average time of dielectric relaxation of the depolarization were found as the magnitude of the polarizing electric field increased.These findings have been interpreted in the framework of the notion of participation in the recharge of localized states more distant from the Fermi level in the crystallites of zinc-oxide ceramics under increased polarizing fields.