Enhanced photovoltaic performance and morphological control of the PbS counter electrode grown on functionalized self-assembled nanocrystals for quantum-dot sensitized solar cells via cost-effective chemical bath deposition

Abstract

This study describes the synthesis of monodispersed PbS nanocrystals by a facile chemical bath deposition and cost-effective approach. PbS counter electrodes (CEs) were used to grow high-quality thin films containing cube-shaped nanocrystals or nanodendrites. The size and shape of the PbS nanocrystals can be easily controlled by varying the deposition time. Quantum dot-sensitized solar cells (QDSSCs) were made and showed improved performance using the PbS CEs obtained with a deposition time of 2 h. The nanocrystal structured PbS CE in QDSSCs under one-sun illumination (AM 1.5, 100 mW cm⁻²) yielded a high short circuit current density (J_sc) of 11.20 mA cm⁻², an open circuit voltage (V_oc) of 0.560 V, a fill factor (FF) of 0.55, and a power conversion efficiency (η) of 3.48%. These values are much higher than those of the Pt CE (J_sc = 79.29 mA cm⁻², V_oc = 0.604, FF = 0.28, and η = 1.58%). The concentration of acetic acid plays an important role in deciding the size and shape of the PbS nanocrystals in the nucleation and growth process. The PbS strongly adhered to the FTO substrate due to the acetic acid, which acts as a stabilizer and a strong reagent in this one-step preparation. The performance of the PbS CE was improved by the surface morphology, which enables rapid electron transport and a lower electron recombination rate for the polysulfide electrolyte redox couple. Electrochemical impedance spectroscopy and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the PbS and Pt CEs.