Photoelectrochemical Formation of Polysulfide at PbS QD-Sensitized Plasmonic Electrodes

Effective electron-hole separation is a key to enhance photoenergy conversion of semiconductor quantum dot (QD)-sensitized plasmonic solar cells. However, in contrast to intense studies on electron transfer, hole transfer from QDs and consequent chemical reactions with donors in electrolytes remain unclear. Herein, in situ electrochemical surface-enhanced Raman scattering (SERS) measurement on a PbS QD-sensitized TiO₂/Au/TiO₂ photoelectrode indicated formation of cyclo-octasulfur (α-S₈) via tuning the electrochemical potential. A photocurrent density of 100 nA/cm² was recorded simultaneously even with an extremely low QD loading. Two-dimensional correlation analysis of the SERS revealed subsequent formation of S₈^- and S₄^2- at -1.1 to -0.1 V (vs Ag/AgCl), S₈ from -0.3 V, and S₅^2- and S₆^2- at ≥0.2 V via complex disproportionation reactions. The sensitive detection is attributed to the enhanced electromagnetic field of localized surface plasmon resonance, which provides a better understanding of charge separation processes in QD-sensitized solar cells.