Low Temperature Preparation of PbS Thin Films by Chemical Bath Deposition and the Photovoltaic Performance in Heterojunction Solar Cells

Abstract

PbS thin films were successfully prepared by chemical bath deposition at low temperature of 40, 50 and 60°C using an improved transparent precursor solution which contained 0.05 M lead nitrate, 0.2 M sodium hydroxide, 0.2 M triethanolamine and 0.06 M thiourea. The obtained PbS thin films appeared smooth and compact, and the crystal sizes were calculated to be 62 nm, 131 nm, 254 nm by Scherrer's equation at deposition temperatures of 40, 50 and 60°C, the corresponding band gaps were estimated to be 1.58 eV, 1.38 eV and 1.20 eV, respectively. The work function of the PbS thin films were measured by Ultraviolet Photoelectron Spectroscopy and they were –4.90, –4.60 and –4.50 eV, respectively. The valence and conduction band edges of the PbS thin films were calculated from the work function and optical band gap values. What is more, the optimized PbS/TiO2 heterojunction thin film solar cell combined with spiro-OMeTAD hole-transport layer was fabricated and obtained the photoelectric conversion efficiency of 0.24%.