Interpretation of a capacitance in polycrystalline solar cells: time domain simulations

In this work, we presented simulations of capacitance of polycrystalline solar cells using time-dependent calculations based on the finite element method. Our starting point was capacitance transient measurements of thin-film CIGS solar cells, which to this day, after twenty years of investigations, do not have the correct theoretical description. We showed, that there exists a model that can be used to explain experimental data, however, it will be not valid without further modification, which will incorporate grain boundaries in it. We developed our software based on deal.ii C++ library using Local Discontinuous Galerkin Method (LDG) and Mixed Finite Element Method (MixFEM) to check how spatial defects can influence the performance of thin-film devices. The results of simulations show that (i) even grain boundary set in parallel to current flow can significantly change properties of a solar cell and the interpretation of its capacitance and that (ii) presence of barriers set perpendicular to current flow, can be indeed responsible for capacitance transient which we know from experiment.