Charged grain boundaries and carrier recombination in polycrystalline thin film solar cells

Abstract

We present analytical relations for the dark recombination current of a $p{n}^{+}$ junction with positively charged columnar grain boundaries in the high defect density regime. We consider two defect state configurations relevant for positively charged grain boundaries: a single donor state and a continuum of both acceptors and donors. Compared to a continuum of acceptor+donor states, or to the previously studied single acceptor+donor state, the grain boundary recombination of a single donor state is suppressed by orders of magnitude. We show numerically that superposition holds near the open-circuit voltage $V_{\mathrm{oc}}$, so that our dark $J(V)$ relations determine $V_{\mathrm{oc}}$ for a given short circuit current $J_{\mathrm{sc}}$. We finally explicitly show how $V_{\mathrm{oc}}$ depends on the grain boundary defect state configurations.

18 pages, 11 figures. In this revised version, we rewrote Eq. (8), corrected language and typos, and took unequal values of mobilities for electrons and holes. This latter change led to making all figures again. The title also changed