Finally, CuP 2 is a stronger light absorber than many established photovoltaic materials, with absorption coefficient rapidly rising to 10 5 cm -1 above its 1.5 eV band gap. Combined with a native doping density in the optimal range for a photovoltaic absorber in a pn junction solar cell (10 15 cm -3 -10 17 cm -3 ), we conclude that CuP 2 may deserve more detailed optoelectronic characterization.