Fig. 2: Crystal structure and bandgap.

a Schematic crystal structure of Pb_0.98Na_0.02Se−x% AgInSe₂ (LISS). b Powder XRD patterns of LISS. c Refined lattice constants of LISS. d Room temperature infrared spectra for PbSe−x% AgInSe₂ and Pb_0.98Na_0.02Se−x% AgInSe₂.