Accurate explicit equations for the fill factor of real solar cells-Applications to thin-film solar cells

ABSTRACT Even within the simplest real solar cell model, the exact value of the fill factor (FF) is only computable by numerical calculations. Here, we perform approximations to the power–voltage curve given by the one‐diode model with series and shunt resistance losses, obtaining explicit expressions for the voltage and current at the maximum power point, and thus an explicit approach for the FF. Over a broad range of possible solar cell parameters, including cells where the impact of shunt losses on the fill factor is not negligible, the approximate equations yield relative errors typically around 1%. The equations are applied to explore the dependence of FF on alternative buffer material thickness of organic solar cells, and to investigate the incidence of shunt and series resistance losses on the FF of Cu(In,Ga)Se2 solar cells under indoor illumination conditions. Copyright © 2012 John Wiley & Sons, Ltd. We obtain accurate equations for the fill factor of solar cells suffering from both series and shunt resistance losses. The equations are applied on two examples: visualization of optimum alternative buffer layer thickness of organic solar cells, and investigation of shunt and series resistance limitations to the fill factor of Cu(In,Ga)Se2 solar cells under indoor illumination conditions. The figure shows how our model follows the fill factor of organic solar cell data where series and shunt resistance limit the fill factor.