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Examines the band-gap engineering in CdS/Cu(In,Ga)Se[sub2] (CIGS) solar cells using a numerical device simulation program. Simulation model description; Discussion on band-gap engineering in CIGS base structure; Analysis of two grading concepts.

Abstract: The paper presents a two-dimensional simulation study of a polycrystalline Cu(In,Ga)Se2 (CIGS) solar cell with various shapes of grains inside the CIGS absorber layer. The grain boundaries (GBs) with a diverse valence-band offset (VBO) and the density of defect states (N tA) are considered so as to evaluate their effects on the performance of the CIGS cell. The numerical simulations show that a CIGS cell with column-like grains can achieve a high conversion efficiency (η), while the η of a CIGS cell with diamond-like grains is low if the VBO at the GBs exceeds 0.4eV. The VBO at which the η of the CIGS cell with diamond-like grains peaks is found at 0.20–0.27eV. A favorable VBO mainly depends on the shape of the grains, but it also depends on the N tA. The simulations of the CIGS cells in the substrate and superstrate configurations showed that their performances change if the VBO is varied. This result also implies that the configuration of the CIGS cell is important and the substrate configuration with larger grains in the space-charge region has a considerable advantage if the VBO ranges from 0eV to 0.2eV. [Copyright &y& Elsevier]

Abstract: A steady-state numerical model of dye-sensitized solar cell is based on continuity and transport equations for electrons, iodide and triiodide ions. The cell model consists of an active layer, where photovoltaic effect including diffusion of electrons in mesoporous TiO2 and ions in electrolyte takes place, and a bulk electrolyte layer, where only ions diffuse. Exponential distribution of trap states in TiO2 and Gaussian distributions of energy levels in the electrolyte within active layer are included in modeling of the recombination dynamics, according to Shockley-Read-Hall statistics and Marcus-Gerischer electron transfer theory. Recombinations at the front contact and a voltage drop at the platinum covered back contact are included in the model. Simulation results are compared with the measured current–voltage characteristics at different light intensities. In particular, light intensity dependence of open circuit voltage is studied over 4 decades. Optimization of cell efficiency regarding active layer and electrolyte layer thickness is carried out. Simulation results show that best efficiency is achieved when electrolyte layer thickness is minimized as much as possible and that active layer thickness is traded off with respect to recombination rates and/or diffusion limited current determined with the selection of the electrolyte. [Copyright &y& Elsevier]

Abstract: A route of optical and electrical modeling of dye-sensitized solar cells (DSSCs) has been developed and validated within a set of test structures. The optical model is based on one-dimensional semi-coherent optical simulator SunShine, in which nanoporous active layer was successfully modelled as effective medium layer with effective scattering of light at its front and back surface interface using effective roughness. The electrical model is based on a pseudo-homogeneous active layer using drift–diffusion transport equations for free electron and ion transport. In both models, input parameters have been extracted from measured performance of test devices and main optical and electrical losses have been quantitatively identified for ionic liquid based DSSC structures, having 7 or 14μm thick active layer. [ABSTRACT FROM AUTHOR]