Radiative transitions in BaCd2P2 solar material

Zintl phosphide BaCd2P2 (BCP) has recently received attention as a promising impurity- and defect-tolerant solar absorber. It has been found to exhibit bright band-to-band photoluminescence (PL) comparable to that of GaAs. In this work, we systematically investigate the mechanisms of radiative and nonradiative recombination in BCP by studying the band-to-band and defect PL emissions. From the temperature quenching of the band-to-band PL, we find that BCP exhibits an apparent activation energy for nonradiative recombination similar to that of GaAs. Furthermore, both materials possess radiative shallow defects with PL emissions near their respective bandgaps. In both cases, these defect emissions arise from free-to-bound transitions. By combining first-principles calculations and experiments, we find that the shallow radiative-defect emissions are most consistent with Ba vacancies (VBa) in BCP and B-on-As substitutional defects (BAs) in GaAs. The former is supported by the suppression of shallow-defect PL emission in Ba-rich BCP samples. Finally, we discuss emissions from deep defects at approximately 0.95 eV at low temperatures, which are present in both materials.