G. F. Novikov

Study of the recombination process at crystallite boundaries in CuIn1 − xGaxSe2 (CIGS) films by microwave photoconductivity

The loss kinetics of photogenerated charge carriers in thin polycrystalline chalcopyrite CuIn1−xGaxSe2 (CIGS) films has been studied by microwave photoconductivity (at 36 GHz). The films were synthesized using the ampoule method and three variants of physical vapor deposition with subsequent selenization: magnetron sputtering, thermal deposition, and modified thermal deposition with intermetallic precursors. The photoconductivity was excited by 8-ns nitrogen laser pulses with maximum intensity of 4 × 1014 photons/cm per pulse. Measurements were performed in the temperature range 148–293 K. The photoresponse amplitude is found to depend linearly on the sizes of coherent-scattering regions in the film grains, which were calculated from X-ray diffraction data. The photoresponse decay obeys hyperbolic law. The photoresponse half-decay time increases with a decrease in both temperature and light intensity. It is shown that the recombination of free holes with trapped electrons is very efficient near the crystallite boundaries.

The formation of MoS2 secondary phase at the Cu—Zn—Sn—S/Mo interface during the sulfurization process of Cu—Zn—Sn precursor films

We report on the influence of the sulfurization conditions on the MoS2 secondary phase formation in Cu—Zn—Sn—S thin films synthesized by thermal evaporation method of metals and intermetallics that can be used for the formation of absorbing layers of solar cells. The dependence between photoconductivity and the intensity of the base line of MoS2 was found in Raman spectra, which is described by a curve with characteristic maximum. It was found that the secondary phase formation on the Cu—Zn—Sn—S/Mo boundary and photoconductivity of sulfurized films are strongly dependent on the applied temperature conditions. Specifically, films without MoS2 phase have a low photoconductivity, whereas a high photoconductivity was observed for the films with significant content of secondary phase.

Microstructure and Raman Scattering of Cu 2 ZnSnSe 4 Thin Films Deposited onto Flexible Metal Substrates

Cu2ZnSnSe4 thin films are produced by selenizing electrochemically layer-by-layer deposited and preliminarily annealed Cu–Zn–Sn precursors. For flexible metal substrates, Mo and Ta foils are used. The morphology, elemental and phase compositions, and crystal structure of Cu2ZnSnSe4 films are studied by scanning electron microscopy, X-ray spectral microanalysis, X-ray phase analysis, and Raman spectroscopy.

Dielectric spectroscopy study of cyanate ester oligomer curing kinetics

The evolution of dielectric properties during the cyanate ester oligomer curing process was studied in the electric field frequencies range of 10–2—105 Hz. The kinetic of the curing process was investigated using the acquired data for complex dielectric permittivity and conductivity. It is demonstrated that, along with the formation of the polymer network, a microphase separation of the reaction intermediate, namely carbamate, takes place during the trimerization reaction. It is manifested in the frequency spectra as the Maxwell—Wagner polarization.

Effect of Precursor Mixture Composition on the Phase Composition and Electrical Transport Properties of Cu1.85ZnSnS4 and Cu1.5Zn1.15Sn0.85S4 Kesterite Solid Solutions Prepared in Molten KI

We have studied the effect of precursor mixture composition on the phase composition and electrical transport properties of Cu1.85ZnSnS4 and Cu1.5Zn1.15Sn0.85S4 solid solutions with the kesterite structure, prepared by reacting binary sulfides and sulfur in molten KI, and found conditions for the synthesis of Cu1.85ZnSnS4 and Cu1.5Zn1.15Sn0.85S4 solid solutions free from inclusions of impurity phases. The Cu1.5Zn1.15Sn0.85S4 and Cu1.85ZnSnS4 solid solutions have been shown to be p-type semiconductors.

Lifetime of Excess Electrons in Cu-Zn-Sn-Se Powders

The method of time-resolved microwave photoconductivity at a frequency of 36 GHz in the range of temperatures of 200–300 K is used to study the kinetics of the annihilation of charge carriers in Cu–Zn–Sn–Se powders obtained by the solid-phase method of synthesis in cells. The lifetime of excess electrons at room temperature is found to be shorter than 5 ns. The activation energy for the process of recombination amounted to Ea ~ 0.054 eV.

Effect of the chemical composition of Cu–In–Ga–Se layers on the photoconductivity and conversion efficiency of CdS/CIGSe solar cells

The effect of the [Ga]/[In+Ga] ratio of gallium and indium on the microwave photoconductivity of Cu–In–Ga–Se (CIGSe) films and on the efficiency of solar cells fabricated in accordance with the same technology is investigated. According to the observations of a field-emission scanning electron microscopy (FESEM), the grain size decreases with increasing Ga content. With increasing gallium content in the samples, the photogenerated-electron lifetime and the activation energy of the microwave photoconductivity also decrease. The changes in the activation energy of the through conduction in darkness are less than 20%. Analysis of the obtained data shows that the known effect of the gallium gradient on the efficiency should be associated with modification of the internal structure of grains instead of with their boundaries.

One-step electrochemical synthesis of Cu—Zn—Sn—Se precursor thin films from solutions containing lactic acid

The influence of the conditions of electrochemical deposition of Cu—Zn—Sn—Se precursor thin films from solutions containing lactic acid on their optical and electrophysical properties was studied. It was found that an additional annealing step of precursor films in a selenium atmosphere at 550 °C is necessary for the preparation of single-phase polycrystalline photoconducting Cu—Zn—Sn—Se films with a band gap energy equal to ~1 eV. The obtained semiconductor CZTSe materials satisfy the composition and property requirements imposed on absorbing layers in solar panels.