Charged grain boundaries reduce the open-circuit voltage of polycrystalline solar cells-An analytical description.

Analytic expressions are presented for the dark current-voltage relation J(V ) of a pn+ junction with positively charged columnar grain boundaries with high defect density. These expressions apply to non-depleted grains with sufficiently high bulk hole mobilities. The accuracy of the formulas is verified by direct comparison to numerical simulations. Numerical simulations further show that the dark J(V ) can be used to determine the open-circuit potential Voc of an illuminated junction for a given short-circuit current density Jsc. A precise relation between the grain boundary properties and Voc is provided, advancing the understanding of the influence of grain boundaries on the efficiency of thin film polycrystalline photovoltaics like CdTe and Cu(In, Ga)Se2.