Empirical J-V modelling of CIGS solar cells

Chalcopyrite based solar modules combine the advantages of thin film module technology with the stability of crystalline silicon cells. Therefore chalcopyrite based modules can potentially take up a large part of the PV market. Today the efficiency of lab scale devices is close to 20 %, comparable to the best multicrystalline silicon cells. Physical insight in the electronic device structure is essential to develop devices with even higher efficiencies. To analyse the cells we measure J-V curves, both dark and light different light intensities, Jsc-Voc curves, spectral response measurements QE(λ) and capacitance measurements. The diode parameters saturation current J0, ideality factor n, series resistance Rs and shunt conductance Gsh are extracted form the dark, light and Jsc-Voc curves. We investigated the light dependence of these parameters at room temperature for different CIGS cells. In this article we will introduce new interpretation schemes: a comparison of the shape of the J-V curves measured over 4 decades of illumination intensity with simulations based on a one diode model, and a study of the fill factor loss calculated ideal FF0 minus measured FF as a function of Jsc/Voc or Voc/Jsc, obtained by varying the illumination intensity. The interpretations proposed here can help solar cell developers in finding causes for a too low fill factor FF. 1

Analysis of graded band gap solar cells with SCAPS

To simulate the complicated, graded structure of modern thin film CIGS solar cells, we followed a �material driven� approach. Each layer is considered as a compound A1-yBy; the desired composition grading y(x) over a layer is set; all materials properties are specified for the pure materials A and B; finally, the local materials properties are derived from the local composition. This strategy was implemented in our thin film solar cell simulation software SCAPS.The new facility was used to study CIGS based thin film solar cells with a graded absorber layer. We showed that a grading strategy with a Ga-poor bulk and narrow Ga-rich layers at both ends of the absorber can indeed lead to a more favourable trade-off between Jsc and Voc than can be obtained with uniform CIGS absorbers. However, this result depends on the specific assumptions on recombination

Electrical characteristics of Cu(In,Ga)Se2 thin films solar cells on metallic foil substrates

Flexible thin-film solar cells offer distinct advantages over cells on rigid glass substrates, but theirefficiency is yet somewhat lower. When using metallic foil substrates, diffusion of impurities from the metalsubstrate to the CIGS cell should be avoided or be under control. Here the electrical characteristics of thin film CIGSsolar cells on metallic substrate foils are studied in order to assess the influence of the substrate on the internaloperation of the solar CIGS cell. We therefore characterised the cells by room temperature I-V, C-V, C-f , QE(�É) andtemperature dependent I-V-T, C-V-T, C-f-T measurements.The efficiency of the best cells studied is in the 13 % range. The apparent doping density profile NA(x), deduced fromroom temperature C-V measurements, is correlated with the nature of the barrier/contact layers. NA(x) is in the 1016cm-3 range, and increasing towards around 2�~1017 cm-3 towards the junction, possibly be due to indium vacanciesnear the heterointerface. This was further evidenced by studying the temperature dependence of C-f-T measurements.Analysis o

Numerical simulation of thin film solar cells: practical exercises with SCAPS

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