The synthesis and characterization of lead sulfide with cube-like structure as a counter electrode in the presence of urea using a hydrothermal method

High-performance PbS particles with cube-like structure were deposited onto fluorine-doped tin oxide glass substrates using a hydrothermal method. The PbS particles were used as an efficient counter electrode (CE) for polysulfide redox reactions in CdS/CdSe quantum dot-sensitized solar cells (QDSSCs). The deposition time and urea concentration were optimized to prepare the PbS CEs. The morphology becomes smoother and the surface roughness increases with the 0.3 M urea CE, which was confirmed by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Under full sunlight illumination, QDSSCs with the optimized 0.3 M urea CE achieved an efficiency of 3.83% (V-oc = 0.55 V, J(sc) = 13.17 mA cm(-2), and FF = 0.52). This value is higher than those for the 0 M urea cell (eta = 2.47%, J(sc) = 10.60 mA cm(-2)) and Pt-based cell (eta = 1.32%, J(sc) = 5.85 mA cm(-2)). Characterization by electrochemical impedance spectroscopy (EIS) and Tafel polarization indicated that the PbS cube-like CEs have lower charge transfer resistance at the CE/electrolyte interface (R-CE) and superior electrochemical catalytic ability. However, R-CE increased with increasing urea concentration (urea 40.3 M), and therefore, the fill factor decreased for the PbS CEs. The influence of different urea concentrations is discussed in detail.