Fig. 1: Materials design and characterizations.

a Material design strategies. XRD patterns and Rietveld refinement plots of b HESSe, c LESSe and d CuS samples. e SEM image, f TEM image, g HRTEM image, h SAED pattern, i HAADF-STEM image and the corresponding EDS elemental mappings of Cu, Sn, Sb, Bi, Mn, S and Se for HESSe.