Thin films of Cu₂SnS₃ and Cu₃SnS₄ were grown by sulfurization of dc magnetron sputtered Sn–Cu metallic precursors in a S₂ atmosphere. Different maximum sulfurization temperatures were tested which allowed the study of the Cu₂SnS₃ phase changes. For a temperature of 350 °C the films were composed of tetragonal (I-42m) Cu₂SnS₃. The films sulfurized at a maximum temperature of 400 °C presented a cubic (F-43m) Cu₂SnS₃ phase. On increasing the temperature up to 520 °C, the Sn content of the layer decreased and orthorhombic (Pmn21) Cu₃SnS₄ was formed. The phase identification and structural analysis were performed using x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) analysis. Raman scattering analysis was also performed and a comparison with XRD and EBSD data allowed the assignment of peaks at 336 and 351 cm⁻¹ for tetragonal Cu₂SnS₃, 303 and 355 cm⁻¹ for cubic Cu₂SnS₃, and 318, 348 and 295 cm⁻¹ for the Cu₃SnS₄ phase. Compositional analysis was done using energy dispersive spectroscopy and induced coupled plasma analysis. Scanning electron microscopy was used to study the morphology of the layers. Transmittance and reflectance measurements permitted the estimation of absorbance and band gap. These ternary compounds present a high absorbance value close to 10⁴ cm⁻¹. The estimated band gap energy was 1.35 eV for tetragonal (I-42m) Cu₂SnS₃, 0.96 eV for cubic (F-43m) Cu₂SnS₃ and 1.60 eV for orthorhombic (Pmn21) Cu₃SnS₄. A hot point probe was used for the determination of semiconductor conductivity type. The results show that all the samples are p-type semiconductors. A four-point probe was used to obtain the resistivity of these samples. The resistivities for tetragonal Cu₂SnS₃, cubic Cu₂SnS₃ and orthorhombic (Pmn21) Cu₃SnS₄ are 4.59 × 10⁻² Ω cm, 1.26 × 10⁻² Ω cm, 7.40 × 10⁻⁴ Ω cm, respectively.

In this paper, co-evaporation of Cu(In,Ga)Se₂ (CIGS) in an inline single-stage process is used to fabricate solar cell devices with up to 18.6% conversion efficiency using a CdS buffer layer and 18.2% using a Zn_1-xSn_xO_y Cd-free buffer layer. Furthermore, a 15.6-cm² mini-module, with 16.8% conversion efficiency, has been made with the same layer structure as the CdS baseline cells, showing that the uniformity is excellent. The cell results have been externally verified. The CIGS process is described in detail, and material characterization methods show that the CIGS layer exhibits a linear grading in the [Ga]/([Ga]+[In]) ratio, with an average [Ga]/([Ga]+[In]) value of 0.45. Standard processes for CdS as well as Cd-free alternative buffer layers are evaluated, and descriptions of the baseline process for the preparation of all other steps in the Ångström Solar Center standard solar cell are given.

In this work, tin selenide thin films (SnSe_x) were grown on soda lime glass substrates by selenization of dc magnetron sputtered Sn metallic precursors. Selenization was performed at maximum temperatures in the range 300 °C to 570 °C. The thickness and the composition of the films were analysed using step profilometry and energy dispersive spectroscopy, respectively. The films were structurally and optically investigated by X-ray diffraction, Raman spectroscopy and optical transmittance and reflectance measurements. X-Ray diffraction patterns suggest that for temperatures between 300 °C and 470 °C, the films are composed of the hexagonal-SnSe₂ phase. By increasing the temperature, the films selenized at maximum temperatures of 530 °C and 570 °C show orthorhombic-SnSe as the dominant phase with a preferential crystal orientation along the (400) crystallographic plane. Raman scattering analysis allowed the assignment of peaks at 119 cm⁻¹ and 185 cm⁻¹ to the hexagonal-SnSe₂ phase and those at 108 cm⁻¹, 130 cm⁻¹ and 150 cm⁻¹ to the orthorhombic-SnSe phase. All samples presented traces of condensed amorphous Se with a characteristic Raman peak located at 255 cm⁻¹. From optical measurements, the estimated band gap energies for hexagonal-SnSe₂ were close to 0.9 eV and 1.7 eV for indirect forbidden and direct transitions, respectively. The samples with the dominant orthorhombic-SnSe phase presented estimated band gap energies of 0.95 eV and 1.15 eV for indirect allowed and direct allowed transitions, respectively.

In this work, we investigated structural, morphological, electrical, and optical properties from a set of ${\text{Cu}}_2\text{Zn}\text{Sn}{\text{S}}_4$ thin films grown by sulfurization of metallic precursors deposited on soda lime glass substrates coated with or without molybdenum. X-ray diffraction and Raman spectroscopy measurements revealed the formation of single-phase ${\text{Cu}}_2\text{Zn}\text{Sn}{\text{S}}_4$ thin films. A good crystallinity and grain compactness of the film was found by scanning electron microscopy. The grown films are poor in copper and rich in zinc, which is a composition close to that of the ${\text{Cu}}_2\text{Zn}\text{Sn}{\text{S}}_4$ solar cells with best reported efficiency. Electrical conductivity and Hall effect measurements showed a high doping level and a strong compensation. The temperature dependence of the free hole concentration showed that the films are nondegenerate. Photoluminescence spectroscopy showed an asymmetric broadband emission. The experimental behavior with increasing excitation power or temperature cannot be explained by donor-acceptor pair transitions. A model of radiative recombination of an electron with a hole bound to an acceptor level, broadened by potential fluctuations of the valence-band edge, was proposed. An ionization energy for the acceptor level in the range 29–40 meV was estimated, and a value of $172\pm 2$ meV was obtained for the potential fluctuation in the valence-band edge.