Exploring p-type dopants in the Zintl phosphide AM₂P₂ solar absorbers

The Zintl phosphides AM₂P₂ (A=Ca, Ba, and M=Cd, Zn) have recently been proposed as a new class of thin-film solar absorbers because of their attractive optoelectronic and defect properties. Our previous work found that these materials could be used as a p-type absorber layer for p-n junction type solar cells. Using first-principles hybrid functional calculations, we systematically explored potential dopants that could lead to adequate p-type doping in the Zintl phosphides. The potential p-type dopants that we considered span quite a range of chemistry, including alkali elements (Na and K) and group 11 elements (Cu and Ag) for substitution of the A and M sites. We also addressed the dopant self-compensation and compensation by other intrinsic donor defects. Our results identify K in BaCd₂P₂ and Ag and Cu in CaCd₂P₂ and CaZn₂P₂ as promising p-type dopants under P-rich growth conditions.