Large-grained Sb2S3 thin films with Sn-doping by chemical bath deposition for planar heterojunction solar cells

Herein, the growth of large-grained and compact Sb2S3 thin films with good electrical properties by Sn doping using a chemical bath deposition (CBD) and annealing approach is detailed. Sn-doped Sb2S3 thin films were prepared using the CBD method with SbCl3, SnCl2.2H2O, and Na2S2O3 as source materials, and ethylenediamine tetraacetic acid (EDTA) as the complexing agent at 40 ° C for 3 h followed by annealing at 250 °C for 30 min under Ar ambience. Un-doped Sb2S3 films exhibited an orthorhombic crystal structure with lattice parameters of a= 1.142 nm, b= 0.381 nm, and c= 1.124 nm, crystalline grain sizes of 100 nm, a direct optical band gap of 1.70 eV, p-type electrical conductivity with high electrical resistivity, and low hole mobility. With Sn doping, a significant increase in the grain size of the films from 6 to >10μm was observed with increasing Sn content from 1.0 to 5.5 at% followed by a decrease in the grain size. The direct optical band gap of the films was 1.71-1.72 eV. By varying Sn at%, the electrical resistivity of the films decreased, and hole mobility increased from 117 to 205 cm2 V−1 s−1 up to 5.5 at% and decreased to 166 cm2 V−1 s−1 at 7.2 at%. With the addition of 1.0-5.5 at% Sn in the Sb2S3 films, the grain growth and electrical properties of the films were drastically enhanced, which is beneficial for the fabrication of planar heterojunction solar cells.