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

Abstract

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 (η = 2.47%, J_sc = 10.60 mA cm⁻²) and Pt-based cell (η = 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 >0.3 M), and therefore, the fill factor decreased for the PbS CEs. The influence of different urea concentrations is discussed in detail.