A detailed analysis of the radiative recombination processes in CuxGaySe2 epitaxial layers is presented aiming at an investigation of the intrinsic defect levels as a function of chemical composition CuxGaySe2 is grown by metalorganic vapor phase epitaxy to allow a precise control of composition Temperature and excitation intensity dependent photoluminescence is used to identify different recombination mechanisms and to determine the ionization energies of the defect levels involved Defect-correlated optical transitions in Cu-rich epilayers are described in a recombination model consisting of two acceptor and one donor levels showing ionization energies of (60±10) meV, (100±10) meV, and (12±5) meV, respectively The identification of a shallow compensating donor in CuxGaySe2 and the assignment of the 100 meV state to an acceptor are the most important new aspects in this model Photoluminescence properties of layers showing Ga-rich compositions are discussed in a model of highly doped and highly compen

Radiative recombination via intrinsic defects in CuxGaySe2

III−VI and I−III−VI semiconductors with anomalous grain boundaries have been actively studied for high efficiency photovoltaic applications. Nanowire morphology can provide a well-defined nanodomain for studying grain boundary and p−n junction physics for improving solar cell efficiency. We report the synthesis of In2Se3 and CuInSe2 single crystalline nanowires via a Au-catalyzed vapor−liquid−solid growth. Superlattice forms in In2Se3 nanowires at room temperature and a reversible superlattice transformation takes place at 200 °C. Cu concentration in CuInSe2 nanowires can be controlled, and nanowires show a dependence of crystal structure on Cu concentration.

Synthesis and Phase Transformation of In2Se3 and CuInSe2 Nanowires

Prospects of wide-gap chalcopyrites for thin film photovoltaic modules

What are the solar cell efficiencies that we can strive towards? We show here that several simple criteria, based on cell and module performance data, serve to evaluate and compare all types of today's solar cells. Analyzing these data allows to gauge in how far significant progress can be expected for the various cell types and, most importantly from both the science and technology points of view, if basic bounds, beyond those known today, may exist, that can limit such progress. This is important, because half a century after Shockley and Queisser (SQ) presented limits, based on detailed balance calculations for single absorber solar cells, those are still held to be the only ones, we need to consider; most efforts to go beyond SQ are directed towards attempts to circumvent them, primarily via smart optics, or optoelectronics. After formulating the criteria and analyzing known loss mechanisms, use of such criteria suggests–additional limits for newer types of cells, Organic and Dye-Sensitized ones, and their siblings,–prospects for progress and–further characterization needs, all of which should help focusing research and predictions for the future.

/pdf/assessing-possibilities-and-limits-for-solar-cells-5fnn2flo1r.pdf

Assessing Possibilities and Limits for Solar Cells

We report the growth and characterization of improved efficiency wide-bandgap ZnO/CdS/CuGaSe2 thin-film solar cells. The CuGaSe2 absorber thickness was intentionally decreased to better match depletion widths indicated by drive-level capacitance profiling data. A total-area efficiency of 9·5% was achieved with a fill factor of 70·8% and a Voc of 910 mV. Published in 2003 by John Wiley & Sons, Ltd.

/pdf/improved-performance-in-zno-cds-cugase2-thin-film-solar-31crngcgsk.pdf

Improved performance in ZnO/CdS/CuGaSe2 thin-film solar cells

Heterojunctions, such as ZnO/CdS/CuGaSe2, were fabricated for photovoltaic applications. Optimization of device structures based on monocrystalline CuGaSe2 led to the highest-to-date power conversion efficiencies for CuGaSe2 solar cells. At room temperature under 100 mW/cm2 AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm2, and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination intensity and temperature, spectral response and electron-beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assisted by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias ofV > 0.5 V or an illumination level ofP > 10 mW/cm2. Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.

CuGaSe2 solar cells with 9.7% power conversion efficiency

Heterojunctions, such as ZnO/CdS/CuGaSe2, were fabricated for photovoltaic applications. Optimiza- tion of device structures based on monocrystalline CuGaSe2 led to the highest-to-date power conversion efficiencies for CuGaSe2 solar cells. At room temperature under 100 mW/cm 2 AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm 2, and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination inten- sity and temperature, spectral response and electron- beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assist- ed by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias of V > 0.5 V or an illumination level of P > 10 mW/cm 2. Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.

H. Riazi

Papers

CuGaSe2 solar cells with 9.7% power conversion efficiency

CuGaSe2 solar cells with 9.7% power conversion