White, red and blue light-induced metastabilities in Cu2ZnSnS(4)(Se-4) solar cells were investigated by temperature dependent current-voltage measurements, drive level capacitance profiling, impedance and thermal admittance spectroscopy. A set of devices were studied where white and blue light soaking at room temperature led to degradation of the device performance, while after red light soaking the solar cell efficiency did not change. We observed a significant effect of light soaking on capacitance data measured in both low and high-temperature ranges for these devices. In particular, the net doping concentration extracted from drive-level capacitance profiling substantially increased after light soaking treatments. Low and high-temperature capacitance steps observed in the reference capacitance-frequency spectra were assigned to Fermi level pinning and bulk defects, correspondingly. Light soaking with different-wavelength light led to a shift of both steps toward the high-frequency range, and hence a decrease in the thermal admittance activation energies. A low-frequency 'inductive' loop was detected in the impedance spectra after light soaking, regardless of wavelength. It was proposed that the appearance of the 'inductive' loop is due to the formation of a negative electric field at the highly defected CdS/Cu2ZnSnS(4)(Se-4) hetero-interface. This result also leads us to conclude that such electric field is responsible for the metastable behaviour of these devices at room temperature, while the low temperature metastable changes might have a different origin. We also discuss the methodology for electrical characterization of the metastable solar cells in detail.

We demonstrate a simple approach to fabricate single-phase SnS thin films by thermal vacuum annealing of SnS2 layers obtained by the close-spaced vacuum sublimation method. It was found that the initial non-annealed SnS2 films exhibit typical chemical composition for SnS2 with ratio of Sn/S = 0.49. The structural quality of the SnS2 phase was studied by X-ray diffraction and Raman spectroscopy measurements. In particular, it was established that films have a hexagonal 2H-SnS2 crystal structure. The field emission scanning electron microscope analysis of the surface and cross-section shows plate-like crystallites with an average size of 2 mu m. Annealing of the SnS2 samples was carried out at 300, 400, and 500 degrees C for 30, 60, and 90 min for each temperature, and at 600 degrees C for 30 min. It was shown that concentration of S gradually decreases with increasing annealing temperature and time. The samples annealed at 500 degrees C for 30, 60, and 90 min demonstrate a typical SnS composition ratio of Sn/S = 0.96. Further, by using X-ray diffraction, Raman, and energy dispersive X-ray analysis, we found that annealing of the samples at 500 degrees C for 30, 60, and 90 min provides a phase transition from hexagonal SnS2 to orthorhombic SnS. The shorter annealing time and temperature leads to the mixed SnS, Sn2S3, and SnS2 phase composition. The shape and size of plate-like crystallites remains the same after annealing. However, randomly distributed nano-pores were observed. Transmittance and reflectance measurements of the SnS2 and SnS films show both direct and indirect optical band gaps in the materials. For SnS films a large absorption coefficient of 10(4) -10(5) cm(-1) above the band gap was found. The current-voltage characteristic of the ITO/SnS2/Sn structure shows small rectification current, while the current-voltage curve of ITO/SnS/Sn is linear. The dark resistivity was found to be 1.01 x 10(5) Omega cm and 1.18 x 10(3) Omega cm for SnS2 and SnS films, respectively. The heterojunction structure was obtained by annealing of the SnS2 deposited on the ITO/CdS structure to obtain the SnS phase. The p-SnS/n-CdS heterojunction shows weak photovoltaic response under illumination at AM 1.5 conditions, namely, open circuit voltage (V-oc), short circuit current density (J(sc)), and fill factor (FF) of 0.35 V, 34.08 mu A/cm(2), and 0.42, respectively.

Tin sulphide is a promising absorber material for low-cost and earth abundant thin film solar cells. In this regard, we have studied phase composition, structural, and electrical properties of n-CdS/p-SnS heterostructure obtained by the close spaced vacuum sublimation (CSS) method. Surface and cross-sectional morphology of the structure were studied by using of field emission scanning electron microscope (FESEM). Thickness of the layers (450 nm for SnS and 550 nm for CdS) and growth mechanism were determined directly from heterostructure cross-section. Crystal structure and films purity were studied by X-ray diffraction (XRD) and Raman spectroscopy methods. The light current density-voltage (J-V) characteristic showed small photovoltaic effect with an open-circuit voltage (Voc) of 0.058 mV, a short circuit current density (Jsc) of 3.83 mA/cm2, a fill factor (FF) of 0.41 and an efficiency (η) of 0.092 %.

Herein, we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical-potential space (SCPS) of CZTS at an elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of VCu−−ZnCu+ complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like ZnCu+ antisites are involved in the formation of VCu−−ZnCu+ complex making CuZn− dominant and providing p-type conductivity even for Cu-poor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS d...

Cu 2 ZnSn(S, Se) 4 (CZTSe) is an earth-abundant semiconductor with potential for economical thin-film photovoltaic devices. Short minority carrier lifetimes contribute to low open circuit voltage and efficiency. Deep level defects that may contribute to lower minority carrier lifetimes in kesterites have been theoretically predicted, however very little experimental characterization of these deep defects exists. In this work we use admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) to characterize devices built using CZTSSe absorber layers deposited via both coevaporation and solution processing. AS reveals a band of widely-distributed activation energies for traps or energy barriers for transport, especially in the solution deposited case. DLTS reveals signatures of deep majority and minority traps within both types of samples.

The present paper deals with the laser ablation in CdZnTe crystal irradiated by pulsed infrared laser. Two values of threshold intensities of the laser ablation were determined, namely of about 8.5 and 6.2 MW/cm(2) for the incident and the rear surfaces, correspondingly. Lower intensity of the laser ablation for the rear surface is explained by thermal self-focusing of the laser beam in the CdZnTe crystal due to heating of Te inclusions with a following hydrodynamic expansion. (C) 2015 Elsevier B.V. All rights reserved.

The effect of substrate temperature on the structural and electrical properties, phase composition, and surface morphology of tin disulfide thin (SnS2) films obtained by the close-spaced vacuum sublimation (CSS) method was studied.Scanning electrical microscope (SEM) images of the samples showed that all of the films were poly-crystalline with an average grain size of 0.7-1.2 mu m. The average thickness of the thin films was 1 mu m.Energy dispersive spectroscopy (EDS) analysis showed that all layers had close to stoichiometric atomic composition. Namely, the concentrations of tin and sulfur were 35 and 65% respectively.X-ray diffraction (XRD) study indicated that the samples obtained at 473-723 K mostly contained hexagonal phase SnS2 with high texture along the (002) crystallographic plane. The values of the lattice constants (a and c) of SnS2 thin films increase monotonically with substrate temperature from 0.3637 to 03647 nm and from 0.5703 to 0.5743 nm, respectively.Investigation of the SnS2 films by Raman spectroscopy confirmed the results of XRD studies, namely that the layers have single-phase hexagonal structure of 2H polytype.Studies of the electrical properties of SnS2 thin films showed that the conductivity of the films changed from 1.8 x 10(-4) to 10(-7) (Om.cm)(-1). Analysis of the I-V characteristics in the space-charge limited current (SCLC) mode made it possible to define (E-t1 = (0.52-0.55), E-t2 = (0.46-0.49), E-t3 = (0.43-0.45), and E-t4 = (0.35-0.39) eV), the localized states energy depths in the band gap of the SnS2 thin films. The concentration of these localized states exceeds 1.31 x 10(14) cm(-3). Also, from the measurements of temperature dependent conductivity, several localized states with activation energies of 0.25 and 0.26 eV states were determined. (C) 2016 Elsevier B.V. All rights reserved.

This work was supported by Erasmus Ianus Programme and by the Ministry of Education, Science of Ukraine (Grant No. 0115U003242, 0113U000131) by the National Academy of Sciences of Ukraine (Grants Nos. BС-157-15 and B-146-15) and State Fund for Fundamental Research (project N GP/F61/087).

thin film of SnS2 obtained by close-spaced vacuum sublimation was irradiated by an Nd:YAG laser (lambda = 532 nm) using two intensities of laser radiation of 8.5 MW/cm(2) and 11.5 MW/cm(2). It was shown that laser irradiation leads to evaporation of sulphur from the surface, and the formation of SnS and Sn2S3 phases. The study of samples' cross-section by energy dispersive X-ray analysis reveals that in the case of irradiation at 8.5 MW/cm(2) intensity, the SnS layer is formed only at the surface of the initial SnS2 thin film. The application of more intensive radiation of 11.5 MW/cm(2) leads to changes in chemical composition for the entire thin film. The formation of the predominant SnS phase, which includes a small amount of Sn2S3, was confirmed by the X-ray diffraction and Raman spectroscopy methods, as well as by measurements of optical reflectance and transmittance spectra. It was established that laser irradiation of the samples leads to the coalescence of grains accompanied by smoothing of the surface. The current-voltage characteristics of the ITO/SnxSy/Al samples show an ohmic behaviour in the case of non-irradiated intensity samples; for irradiated samples, the diode behaviour of I-V curves was observed. This is considered as evidence of the formation of p-SnS/n-SnS2 heterojunction by laser irradiation. (C) 2016 Elsevier B.V. All rights reserved.

Polycrystalline Cd1−xZnxTe thick films with thicknesses of about 30μm have been deposited on a Mo coated glass substrate by means of close-spaced vacuum sublimation technique. X-ray diffraction measurements have shown that the films obtained have only cubic zinc blende phase. The influence of Zn concentration on the photoluminescence (PL) spectra of Cd1−xZnxTe films was investigated. This let us determine the nature and energy structure of the intrinsic defects and residual impurities in the films. The presence of the most intense acceptor bound exciton A°X-line for x=0.10 and the lines of localized excitons (x=0.32−0.44) in PL spectra of Cd1−xZnxTe films indicates their fairly good optical quality as well as the p-type conductivity. There were also other intensive broad PL bands, caused by the recombination of donor–acceptor pairs involving complex acceptor centers, extended defects of dislocation type, and microstress in the films. It was also established a correlation between the broadening of exciton lines and the values of microstress in Cd1−xZnxTe thick films. Taking into account the energy position of exciton lines, the concentration dependence of the band gap for the Cd1−xZnxTe thick films is presented.

We report a quasichemical model for point defect equilibrium in Cu2ZnSnS4 (CZTS). An ab initio calculation was used to estimate the changes in the phonon spectrum of CZTS due to trial point defects and further vibrational free energy, which in turn influences the final defect concentrations. We identify the dominant point defects and estimate the free carrier concentrations as functions of the Zn, Cu, and Sn chemical potentials, the sulfur chemical potential being set by the vapor-solid equilibrium with elemental S at the same temperature as the sample (one-zone annealing). As hinted by calculated low formation enthalpies, either the Cu vacancy (VCu−) or Cu on Zn antisite (CuZn−) acceptors are expected to dominate over a wide range of cation chemical potentials. However, the sulfur vacancy (VS2+) becomes a dominant compensating donor especially for one-zone annealing conditions. We also find that different native defects induce distinct perturbations to the vibrational free energy, resulting in non-trivial qualitative and quantitative shifts in the defect equilibrium. At typical annealing temperatures and Zn-rich conditions, this may introduce especially strong modulations in the concentrations of ZnSn2− and, contrary to enthalpic predictions, of ZnCu+ compensating donors. The modeling indicates that one-zone processing should result in CZTS, which is p-type but extremely compensated because native donor defects are stabilized by the low Fermi level and finite-temperature effects.

The temperature-dependent conductivity of Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of different sputtered ZnS/Cu/Sn stacks and also of the same stack annealed for different times was investigated from 30-300 K. Fitting of the through-thickness conductivity requires a model including Mott variable-range hopping (M-VRH), nearest-neighbor hopping (NNH), and thermionic emission over grain boundary (GB) barriers. The GB barrier height varies sensitively from 50–150 (±5) meV with annealing and especially with [Cu]/([Zn] + [Sn]) ratio but is independent of [Zn]/[Sn] ratio. These results are critical for understanding the behavior of solar cells based on polycrystalline CZTS absorber layers.

Optical properties of Zn1-xMnxS and Cd1-xMnxTe films, obtained by close-spaced vacuum sublimation technique are investigated. Measuring of optical characteristics layers was carried out by spectrophotometric analysis. This research allowed to obtained spectral distributions of transmittance, reflectance and absorption coefficients of films and to expect band-gap energy of materials.

The native point defects structure in ZnS films obtained by the close-spaced vacuum sublimation technique at different growth conditions has been studied. The energy levels in the band gap were studied by the photoluminescence and injection spectroscopy under monopolar injection conditions. Luminescence spectra were recorded using electrical fluorometer in the range of wavelengths λ=360–710nm under liquid-helium temperature. The point defects structure in the ZnS films was calculated using quasi-chemical formalism. Besides, in order to study the point defects dark voltage–current characteristics using the theory of space charge limited currents was investigated. As a result, dependences of concentration of free carriers and native point defects on technological growth conditions of ZnS films have been received. In the band gap of ZnS a range of localized states with different energy were revealed.

The surface morphology and microstructural characteristic of ZnTe, CdTe and ZnS thin films obtained by close-spaced sublimation technique were investigated. The structural features of layers were examined by XRD, SEM and optical microscopy. Size of coherent scattering regions, lattice microstrain and stacking fault defect concentration were estimated from X-ray diffraction line broadening. The investigation performed elucidates effect of preparation conditions on main structural characteristics of ZnTe, CdTe and ZnS thin films.