High photocurrent performance of nebulizer sprayed Bi₂S₃ thin films by a novel Cu-La doping strategy

Nowadays, chalcogenide-based thin layers are proving a promising light-absorbing material with low cost and are technologically suitable for light to current conversion applications. In this study, for the first time, pristine Bi₂S₃, Bi₂S₃:Cu2%, Bi₂S₃:La2%, and Bi₂S₃:Cu2%:La2% thin films were prepared by nebulizer spray pyrolysis technique on a glass substrate at 300 °C. The obtained XRD pattern confirms the orthorhombic structure of Bi₂S₃ and possesses a maximum crystallite size of 38 nm for Bi₂S₃:Cu: La co-doped sample. Images taken with a FESEM analysis showed the unformed distribution of round shaped grains without any cracks and co-doping leads to the development of slight cluster formation. The optical absorbance spectra of the thin films were observed from the wavelength of 350 nm to 1000 nm, and the co doping process highly strengthen the optical absorbance, which is prerequisite for an efficient photodetector. A lower band gap value of 1.7 eV is achieved for Bi₂S₃: Cu: La thin film. From PL studies, defect emission bands around ∼325 and 525 nm related to band edge emission and sulfur vacancies are obtained. Further, UV photosensing properties of each sample were evaluated. Commendable performance with maximum responsivity (1.24 × 10⁻¹ AW⁻¹), detectivity (1.13 × 10¹⁰ Jones), and EQE (40%) were achieved for Bi₂S₃:Cu:La-sample. The enhanced figures-of-merit are attributed large crystalline size, good crystallinity, lower bandgap and crack free surface. The photo sensing results may widen the field of photosensing application.