Impact of sheet resistance on 2-D modeling of thin-film solar cells

A rigorous mathematical approach was used to find a relation between the transparent-conductive-oxide (TCO) sheet resistance ρS (Ω/□) of a thin-film solar cell and the parameter R (Ω) that describes the TCO resistance in a two-dimensional circuit model. Additionally, the mathematical relationship that connects experimentally derived series resistance RS (Ω cm2) of the solar cell to the TCO sheet resistance ρS (Ω/□) and the bulk semiconductor resistivity ρ (Ω cm) was derived. It was found that the fill factor of the solar cell is governed by a reduced dimensionless TCO sheet resistance that depends only weakly on the type and quality of the solar cell. Parameters corresponding to thin-film Cu(In,Ga)Se2, two-junction a-Si, and an ideal solar cell were used as concrete examples.