Optical and Recombination Parameters of CdS1−xTex Thin Films Obtained by the CMBD Method

This paper presents the results of the photoacoustic, SEM, and surface photovoltage experiments performed on the series of CdS1−xTex thin films. These CdS1−xTex (0 ≤ x ≤ 1) thin films were obtained on the glass substrate by the chemical molecular beam deposition (CMBD) method. The polycrystalline character of these films was revealed by SEM pictures. From the experimental optical characteristics, the optical absorption coefficient spectra of the samples and values of their energy gaps vs. their composition were determined. From the surface photovoltage characteristics, the diffusion lengths of the carriers were also determined.

Influence of the reagents’ ratio on photoelectric and optical properties of perovskite films for photovoltaics

The properties of the synthesized films of organic-inorganic perovskites CH3NH3PbI3 obtained at various ratios of starting reagents (PbI2 and CH3NH3I) have been studied. As a solvent, we used chemically pure dried dimethylformamide (DMF). Organic-inorganic perovskites are promising for photovoltaic applications. It has been shown that regardless of the ratio of the starting reagents, single-phase perovskites are formed, at the same time the microstructure of the films changes significantly. It has been reported photoelectric and optical properties of synthesized films, namely: experimental and theoretical spectral dependences of the low-signal surface photovoltage and transmission. The band gap and the Urbach parameter dependence on the ratio of precursors were determined. It has been found that the materials’ band gap depends on the ratio of precursors and equals to 1.59, 1.62 and 1.57 eV, while the characteristic Urbach energy equals to 18, 19 and 22 meV for the PbI2:CH3NH3I films with PbI2 ratio of 1:1, 1:2 and 1:3, respectively. It has been ascertained that the spectral dependences of the low-signal surface photovoltage are much more sensitive to the material microstructure and its electronic structure close to the absorption edge, while the optical transmission spectra are not so sensitive. The limiting value of the short-circuit current density for the films with different PbI2 and CH3NH3I ratios has been determined.

Synthesis and properties of unsymmetrical porphyrins possessing an isonicotinic acid moiety and phenyl, methoxyphenyl, or chlorophenyl groups

The isonicotinic acid containing porphyrin compounds 5-{4-[3-(4-pyridylcarbonyloxy)propoxy]phenyl}-10,15,20-triphenylporphyrin, 5-{4-[3-(4-pyridylcarbonyloxy)propoxy]phenyl}-10,15,20-tri(4-methoxyphenyl)porphyrin, and 5-{4-[3-(4-pyridylcarbonyloxy)propoxy]phenyl}-10,15,20-tri(4-chlorophenyl)porphyrin are prepared and characterized by 1H NMR, 13C NMR, MS, elemental analysis, IR, and UV-Vis. In addition, their spectroscopic properties are investigated through using the Raman spectroscopy, fluorescence, and surface photovoltage measurements. The influence of different substituents on Raman spectra is small, but their impact on the fluorescence spectra and surface photovoltage measurements is significant. Molecular dynamic simulations and UV-Vis diffuse-reflectance spectra show that these porphyrin compounds are potential semiconductor materials.

Frequency-Dependent Sonochemical Processing of Silicon Surfaces in Tetrahydrofuran Studied by Surface Photovoltage Transients

The field of chemical and physical transformations induced by ultrasonic waves has shown steady progress during the past decades. There is a solid core of established results and some topics that are not thoroughly developed. The effect of varying ultrasonic frequency is among the most beneficial issues that require advances. In this work, the effect of sonication of Si wafers in tetrahydrofuran on the photovoltage performance was studied, with the specific goal of studying the influence of the varying frequency. The applied ultrasonic transducer design approach enables the construction of the transducer operating at about 400 kHz with a sufficient sonochemical efficiency. The measurements of the surface photovoltage (SPV) transients were performed on p-type Cz-Si(111) wafers. Sonication was done in tetrahydrofuran, methanol, and in their 3:1 mixture. When using tetrahydrofuran, the enhanced SPV signal (up to ≈80%) was observed due to increasing sonication frequency to 400 kHz. In turn, the signal was decreased down to ≈75% of the initial value when the frequency is lowered to 28 kHz. The addition of methanol suppressed this significant difference. It was implied that different decay processes with hydrogen decomposed from tetrahydrofuran could be attempted to explain the mechanism behind the observed frequency-dependent behavior.