Bandgap engineering of ZnSnP ₂ for high-efficiency solar cells

ZnSnP ₂, an absorber material for solar cells, transitions from an ordered chalcopyrite to a disordered sphalerite structure at high temperatures. We investigate the electronic structure of both phases, combining a screened hybrid density functional with the special quasi-random structure method. We predict a bandgap reduction of 0.95 eV between the ordered and fully disordered materials. Experimental reports are consistent with partial disorder. Tuning of the order parameter would lead to a family of ZnSnP ₂ phases with bandgaps ranging from 0.75 eV to 1.70 eV, thus providing graded solar cell absorbers from a single material system.