Thin-film (Sb,Bi)2Se3 Semiconducting Layers with Tunable Band Gaps Below 1 eV for Photovoltaic Applications

Polycrystalline $(\mathrm{Sb},\mathrm{Bi}{)}_{2}{\mathrm{Se}}_{3}$ thin-film semiconductors are grown by coevaporation with a subsequent annealing process. It is shown that $\mathrm{Bi}$ can be incorporated into the ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$ lattice, substituting up to approximately 60% of the $\mathrm{Sb}$ atoms, while maintaining the orthorhombic crystal structure. Upon $\mathrm{Bi}$ substitution, the lattice expands mainly along the one-dimensional $(\mathrm{Sb},\mathrm{Bi}{)}_{4}{\mathrm{Se}}_{6}$ ribbons. In addition, the band gap decreases with a direct (indirect) band gap of 0.891 eV (0.864 eV) for a $({\mathrm{Sb}}_{0.4},{\mathrm{Bi}}_{0.6}{)}_{2}{\mathrm{Se}}_{3}$ thin film. A photovoltaic device based on a $(\mathrm{Sb},\mathrm{Bi}{)}_{2}{\mathrm{Se}}_{3}$ absorber is fabricated that displays an open-circuit voltage of 133 mV and a short-circuit current density of $18.4\phantom{\rule{0.1em}{0ex}}\mathrm{mA}/{\mathrm{cm}}^{2}$, demonstrating the potential of this material for infrared detection or multijunction solar-cell applications.