Effect of Zn doping concentration on optical band gap of PbS thin films

Abstract The lead sulfide (PbS) thin films with Zn doping concentration from 0 at.% to 5 at.% were synthesized utilizing chemical bath deposition technique. X-ray diffraction (XRD) revealed that the calculated crystallite size decreased from 20.6 nm to 16.7 nm with the increasing zinc doping concentration. FESEM images showed PbS nanocrystals on the surface of the films exhibited pyramidal shape, and the grain size became smaller with the increasing doping concentration. The AFM results showed that the root mean square roughness of the PbS film has been reduced due to Zn doping. The optical properties of films were explored by UV–vis–NIR spectrophotometer in the range from 400 to 2400 nm, the optical bandgap value of PbS films increased from 1.14 eV to 1.74 eV. All as-deposited films were p-type semiconducting. Among them, the 3 at.% Zn-PbS thin films possessed the lowest resistivity (10.8 Ω -cm), the highest carrier concentration (2.82 × 10 17  cm −3 ) and carrier mobility (11.2 cm −2 V −1 s −1 ). A new ideal bandgap (1.39 eV) absorber composition (1 at.% Zn-doped PbS film) was rationally designed and facilely developed. Our work presents a promising potential for ideal bandgap absorber layer of solar cells.