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

TL;DR

This paper derives analytical expressions for the dark current-voltage behavior of polycrystalline solar cells with charged grain boundaries, linking grain boundary properties to open circuit voltage and improving understanding of efficiency impacts.

Contribution

It provides new analytical formulas for dark current-voltage relations in polycrystalline solar cells with charged grain boundaries, validated by simulations.

Findings

Dark J(V) can determine open circuit voltage V_oc.

Charged grain boundaries significantly reduce V_oc.

Analytical expressions match numerical simulations accurately.

Abstract

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 $V_{\rm oc}$ of an illuminated junction for a given short-circuit current density $J_{\rm sc}$ . A precise relation between the grain boundary properties and $V_{\rm oc}$ is provided, advancing the understanding of the influence of grain boundaries on the efficiency of thin film polycrystalline photovoltaics like CdTe and $\mathrm{Cu(In,Ga)Se_2}$.