(BixSb1−x)2Se3 thin films for short wavelength infrared region solar cells

Abstract

The short-wavelength infrared region of the solar spectrum remains largely untapped. The development of small band gap (0.7–1.1 eV) photovoltaic devices that will complement existing photovoltaic devices can potentially add 6% power conversion efficiency points. Bismuth-alloyed antimony selenide [(Bi_xSb_1−x)₂Se₃] is a potentially suitable light absorber with a tunable band gap in the relevant range. This paper reports a procedure for depositing Bi-alloyed Sb₂Se₃ thin films through close-spaced sublimation (CSS). Continuous thin films with various Bi concentrations and alloying up to 30 at% of Bi into Sb₂Se₃ [Bi/(Bi + Sb) = 0.30] were prepared. The composition, structure, and optical properties of the (Bi_xSb_1−x)₂Se₃ thin films were characterized. A decrease in the optical band gap from 1.17 eV to 0.99 eV has been observed by Bi-alloying (x = 0.30). A three-times decrease in grain size from ∼270 nm (for x = 0.0) to ∼100 nm (for x > 0.11) has been observed. The (Bi_xSb_1−x)₂Se₃ thin films were tested in an FTO/ZnO/CdS/(Bi_xSb_1−x)₂Se₃/Au solar cell structure to find their applicability in photovoltaic devices.