Finding a junction partner for candidate solar cell absorbers enargite and bournonite from electronic band and lattice matching

An essential step in the development of a new photovoltaic (PV) technology is choosing appropriate electron and hole extraction layers to make an efficient device. We recently proposed the minerals enargite (⁠$Cu3AsS4$⁠) and bournonite (⁠$CuPbSbS3$⁠) as materials that are chemically stable with desirable optoelectronic properties for use as the absorber layer in a thin-film PV device. For these compounds, spontaneous lattice polarization with internal electric fields—and potential ferroelectricity—may allow for enhanced carrier separation and novel photophysical effects. In this work, we calculate the ionization potentials for non-polar surface terminations and propose suitable partners for forming solar cell heterojunctions by matching the electronic band edges to a set of candidate electrical materials. We then further screen these candidates by matching the lattice constants and identify those that are likely to minimise strain and achieve epitaxy. This two-step screening procedure identified a range of unconventional candidate junction partners including $SnS2$⁠, ZnTe, $WO3$⁠, and $Bi2O3$⁠.