Near-surface electronic defects and morphology of CuIn[sub 1−x]Ga[sub x]Se[sub 2] (original) (raw)
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Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study
Journal of Physics D: Applied Physics, 2013
Sb doping of Cu(In,Ga)Se 2 (CIGS) solar cells has been reported to exhibit a positive effect on the morphology of the absorber layer, offering a possibility to lower manufacturing cost by lowering the annealing temperatures during the CIGS deposition. In this work electron microscopy, energy-dispersive X-ray spectroscopy and photoluminescence experiments have been performed on cells deposited on soda lime glass substrates, adding a thin Sb layer onto the Mo back contact prior to the CIGS absorber deposition. The defect structure of CIGS solar cells doped with Sb in this way has been investigated and is compared with that of undoped reference cells. The influence of substrate temperature during absorber growth has also been evaluated. For all samples the photoluminescence results can be explained by considering three donor-acceptor pair recombination processes involving the same defect pairs.
Near-surface defect distributions in Cu (In, Ga) Se 2
The density and distribution of point defects in Cu(In,Ga)Se (CIGS) layers used for solar cell applications is critical to the 2 resulting device performance. These devices are generally thought to be limited by recombination in the space-charge region of the collecting heterojunction. The situation is complicated by the presumed presence of an n-type surface layer on the CIGS absorber. Both the surface inversion and space-charge recombination processes are intimately tied to near-surface point defects.
Progress in Photovoltaics: Research and Applications, 1997
This contribution is a summary of an international, interdisciplinary workshop dedicated to defects in chalcopyrite semiconductors and their relation to the device characteristics of thin-®lm solar cells, held on 3±5 June 1996 in Oberstdorf, Germany. Results of dierent characterization methods were brought together to identify common observations. The comparison of results from electrical defect spectroscopy and luminescence investigations con®rmed the presence of energetic distributions of defects throughout the bandgap of chalcopyrite thin ®lms. Electrical defect spectroscopy detects a defect about 280 meV above the valence band edge of Cu(In, Ga)Se 2 regardless of the preparation conditions of the sample. In a solar cell the density of this defect depends on the operation conditions. This observation might be related to the migration of copper in an electric ®eld, which occurs even at room temperature. Other defects appear to be related to processing or impurities. Photoluminescence decay measurements yield time constants of several nanoseconds under low injection conditions. Modelling of the current±voltage characteristics of Cu(In, Ga)Se 2 -based thin-®lm cells suggests that compensating acceptor states in the CdS or at the heterointerface are responsible for the frequently observed cross-overs between the dark and illuminated curves.
Required CIGS and CIGS/Mo Interface Properties for High-Efficiency Cu(In, Ga)Se2 Based Solar Cells
Advances in Materials Physics and Chemistry, 2020
In this work, we have modeled and simulated the electrical performance of CIGS thin-film solar cell using one-dimensional simulation software (SCAPS-1D). Starting from a baseline model that reproduced the experimental results, the properties of the absorber layer and the CIGS/Mo interface have been explored, and the requirements for high-efficiency CIGS solar cell were proposed. Simulation results show that the band-gap, acceptor density, defect density are crucial parameters that affect the performance of the solar cell. The best conversion efficiency is obtained when the absorber band-gap is around 1.2 eV, the acceptor density at 10 16 cm −3 and the defect density less than 10 14 cm −3. In addition, CIGS/Mo interface has been investigated. It appears that a thin MoSe 2 layer reduces recombination at this interface. An improvement of 1.5 to 2.5 mA/cm 2 in the current density (J sc) depending on the absorber thickness is obtained.
Applied Physics Letters, 2009
In-depth resolved composition inhomogeneities of polycrystalline Cu͑In, Ga͒Se 2 ͑CIGS͒ complex layers for high efficiency solar cells were investigated with Raman scattering measurements. In-depth resolved analysis of the frequency of the main CIGS Raman mode in the spectra measured after sputtering of the layers at different depths lead to identification of different compositions across the layer thickness. These data are in good agreement at both qualitative and quantitative levels with the in-depth resolved composition analysis of the samples by sputtered neutral mass spectroscopy. In addition, Raman measurements also allow detection of additional phases as ordered vacancy compounds.
Reinterpretation of defect levels derived from capacitance spectroscopy of CIGSe solar cells
Thin Solid Films, 2009
In this work we make an attempt to clarify ambiguities and to present our present understanding of defects and defect-related phenomena affecting the capacitance characteristics of Cu(In,Ga)Se 2 -based solar cells. We discuss deep defect levels derived from admittance and deep level transient spectroscopy, as well as shallow levels affecting the charge distributions by capacitance-voltage profiling. The discussion includes two types of metastable effects affecting capacitance characteristics: one induced at room temperature by light or voltage bias, and one created at low temperature by red illumination of reverse-biased junction (ROB effect). Recent theoretical achievements on negative-U properties of such intrinsic defects as selenium vacancies and In Cu antisites are used to explain the experimental data. We show that the most prominent level in the admittance spectra is due to the response of interface states combined with contribution of deep V Se -V Cu −/2− acceptor level. We attribute the ROB metastability to the relaxation of In Cu defects upon electron capture. Finally we discuss the influence of these defects on the device efficiency.
ELECTRIC AND CHEMICAL CHARACTERIZATIONS OF THE HETEROINTERFACES IN THE Cu(In,Ga)Se 2 SOLAR CELLS
We have studied Cu(In,Ga)Se 2 chemical and electric behavior and composition engineering. All investigations were carried out on co-evaporated Cu(In,Ga)Se 2 (CIGS) samples onto which different surface etching were applied. XPS was used to determine the composition evolution of the CIGS surface with treatment and CIGS/CdS interface. Electric measurements were studies using admittance spectroscopy and Kelvin probe. Work presented will give a progress report on three years of collaboration relating to the study of the mechanisms of formation of CIGS/CdS interfaces.