Structure and electronic properties of domain walls and stacking fault defects in prospective photoferroic materials bournonite and enargite

Abstract

Bournonite (CuPbSbS3) and enargite (Cu3AsS4) have recently been used as absorber layers in thin-film photovoltaic devices due to their ideal bandgap and ferroelectric properties. An understanding of the ferroelectric domain structure in these materials is required so that the benefits of the internal depolarizing electric fields can be fully exploited. Here, the atomic structure and electronic properties of domain walls (DWs) are elucidated through a combined aberration-corrected scanning transmission electron microscopy and density functional theory study. ∼90° and 180° DWs are observed in bournonite. As the 180° DW is charge neutral, it cannot contribute to the anomalous photovoltaic effect that leads to high open circuit voltages. The ∼90° DW shows a slight offset across the boundary, but the contributions of this to the anomalous photovoltaic effect are negligible. The DWs are also electrically passive, i.e., they do not result in significant recombination and do not block charge carrier transport. A high density of stacking faults (SF) was, however, observed in enargite. The SFs have a large number of defect states within the bandgap, which would lower the device efficiency through Shockley–Read–Hall recombination.