Unravelling the Role of Stacking Disorder on the Optoelectronic Properties of Zn3P2

Abstract Zinc phosphide (Zn3P2) is a promising photovoltaic absorber for thin-film and flexible solar cells due to its earth-abundant composition and favourable optoelectronic properties. Recent advances in epitaxy have enabled the growth of high-quality Zn3P2 thin films despite the challenges posed by its incompatible lattice parameter and thermal expansion coefficient. However, Zn3P2 remains prone to intrinsic extended defects, such as rotated domains, that can limit device performance. Here, using (scanning) transmission electron microscopy, we identify a class of extended defects that appear as planar faults described by displacement vectors lying in the (001) plane. Within a pseudo-cubic description of Zn3P2, we establish a direct correspondence between planar faults and rotated domains, showing that both arise from the flexible ordering of vacant sites in the Zn sublattice. First-principles calculations reveal an extremely low planar-defect formation energy of 2.5 mJ m−2, demonstrating that these defects form at essentially negligible energetic cost, in excellent agreement with their high experimentally observed occurrence. Additional density functional theory calculations show that the studied intrinsic planar defects neither introduce mid-gap electronic states nor significantly perturb the local electrostatic potential, indicating that they are electronically benign. Our results suggest that any connection between the observed planar defects and a reduction in device performance must therefore involve indirect mechanisms, such as strain effects or interactions with other defects.