  The efficiency of a solar cell is often limited by electron-hole
recombination mediated by defect states within the band gap of the photovoltaic
(PV) semiconductor. The Shockley-Read-Hall (SRH) model considers a static trap
that can successively capture electrons and holes. In reality however, true
trap levels vary with both the defect charge state and local structure. Here we
consider the role of metastable structural configurations in capturing
electrons and holes, taking the tellurium interstitial in CdTe as an
illustrative example. Consideration of the defect dynamics, and
symmetry-breaking, changes the qualitative behaviour and activates new pathways
for carrier capture. Our results reveal the potential importance of metastable
defect structures in non-radiative recombination, in particular for
semiconductors with anharmonic/ionic-covalent bonding, multinary compositions,
low crystal symmetries or highly-mobile defects.
