Search

ABSTRACT In order to transfer the potential for the high efficiencies seen for Cu(In,Ga)Se2 (CIGSe) thin films from co-evaporation processes to cheaper large-scale deposition techniques, a more intricate understanding of the CIGSe growth process for high-quality material is required. Hence, the growth mechanism for chalcopyrite-type thin films when varying the Cu content during a multi-stage deposition process is studied. Break-off experiments help to understand the intermediate growth stages of the thin-film formation. The film structure and morphology are studied by X-ray diffraction and scanning electron microscopy. The different phases at the film surface are identified by Raman spectroscopy. Depth-resolved compositional analysis is carried out via glow discharge optical emission spectrometry. The experimental results imply an affinity of Na for material phases with a Cu-poor composition, affirming a possible interaction of sodium with Cu vacancies mainly via In(Ga)Cu antisite defects. An efficiency of 12.7% for vacancy compound-based devices is obtained. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT In this letter, we report externally confirmed total area efficiencies reaching up to 12.9% for CdS/Cu(In,Ga)S2 based solar cells. These are the highest externally confirmed efficiencies for such cells. The absorbers were prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor. Structural, compositional, and electrical properties of one of these champion cells are presented. The correlation between the Ga distribution profile and solar cell properties is discussed. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the role of the non-doped i-ZnO layer in thin-film Cu(In,Ga)Se2 solar cells. A large number of laboratory scale module cells with different non-doped ZnO thicknesses are inspected by JV analysis, lock-in thermography and optical spectroscopy. We find that the role of the i-ZnO layer in our samples is to reduce the impact of randomly occurring electrical shunt paths in the devices. Accordingly, the i-ZnO layer leads to a somewhat smaller spread of device parameters. In the case of absent shunt paths, the device parameters of cells and modules without i-ZnO are similar to those with a thin i-ZnO layer. An effect of i-ZnO on the Voc is not systematically observed. However, for larger i-ZnO thickness, Jsc is systematically reduced, which is identified as due to optical absorption in the i-ZnO layer. We further find by high-resolution lock-in thermography that the junction homogeneity is not affected by the i-ZnO layer. Only the non-linear reverse bias current reduces with increasing i-ZnO thickness-an effect that appears to be independent from the saturation current density. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Polycrystalline Cu(In, Ga)Se2 with Ga-content x=Ga/(In+Ga) ranging from 0.0 (CuInSe2) to 1.0 (CuGaSe2) in heterojunction thin film solar cells were grown by multi-source evaporation. Solar cells with a highest efficiency of η=15.3% need a composition of x≈0.2. At this composition, the c/ a ratio of the lattice constants for the tetragonal lattice equals c/ a=2, indicating ideal tetragonality. These results suggest that low electronic defect densities occur at x≈0.2, due to the smallest possible crystallographic distortion of the tetragonal lattice at this composition. Cells with high efficiencies require grain sizes above 145 nm and a high preferred orientation (P204/P220 pole density ratio) for the grains. [ABSTRACT FROM AUTHOR]

This paper uses an innovative peak profile matching method to determine compositional depth profiles of Cu(In,Ga)(S,Se)2 thin films and other suitable solid-solution compounds. A layer absorption model allows the generation of grazing-incidence diffraction patterns on the basis of the known diffractometer instrument function, compositional depth profiles and the corresponding mass absorption characteristics. In contrast to other methods, the modelling approach exploits the information stored in the shape evolution of the peak profile as a function of incidence angle. A small number of diffraction patterns of the same peak are sufficient to track depth-dependent shifts of the principal lattice parameters. The method is adapted to the specific properties of the chalcopyrite Cu(In,Ga)(S,Se)2 system. In fact, the multinary chalcopyrite compounds grown by physical vapour deposition have some remarkable properties which allow the successful application of the method. Issues like surface roughness, refraction at low incidence angles and their effects upon relative intensities can be successfully circumvented by the modelling approach. Ambiguities in the modelling results are very small and can be minimized by comparison with complementary depth profiles using secondary ion mass spectrometry or cross-sectional energy-dispersive X-ray analysis. [ABSTRACT FROM AUTHOR]

Solar cells based on polycrystalline films of CuIn[sub 1-x]Ga[sub x]Se[sub 2] solid solutions were produced for the first time by the pulsed laser evaporation of source targets. The current-voltage characteristics of the cells were investigated, and the main photoelectrical parameters were ascertained. The optimal concentration of gallium ensuring maximal conversion efficiency of the thin-film solar cells and the films of the solid solutions with a chalcopyrite structure were determined. [ABSTRACT FROM AUTHOR]

Results of the application of polarization spectroscopy of the photosensitivity of ZnO/CdS/Cu(In,Ga)Se[sub 2] thin-film solar cells with different thicknesses of the CdS (50 and 100 nm) and ZnO (500 and 1000 nm) layers are considered. It is established that the induced photopleochroism coefficient is lowered while the quantum efficiency of photoconversion of the solar cells is raised by increasing the thickness of the front layer. The experimental conditions and spectral dependence of the induced photopleochroism are linked with the antireflection properties of the ZnO front layers. It is concluded that photosensitivity polarization spectroscopy can be used for rapid diagnostics of finished solar cells and to optimize their fabrication technology. [ABSTRACT FROM AUTHOR]

The photoelectric properties of thin-film ZnO/CdS/Cu(In,Ga)Se[sub 2] solar cells were studied by polarization photoactive absorption spectroscopy. It was shown that the thin-film solar cells have a high efficiency relative to the intensity of unpolarized radiation in the photon energy range from 1.2 to 2.5 eV. The induced photopleochroism coefficient P[sub I] increases with the angle of incidence of the incident radiation as P[sub I] ∼ θ² and at 70° it reaches 17-20% with photon energy 1.3 eV. Oscillations of the photopleochroism were also observed. These results are discussed taking into account the antireflection effect. The results obtained by us make it possible to use such solar cells as wide-band photosensors for linearly polarized radiation and for monitoring the production of high-efficiency, thin-film solar cells based on ternary semiconductors. [ABSTRACT FROM AUTHOR]