Photoelectrochemical Formation of Polysulfide at PbS QD-Sensitized Plasmonic Electrodes.

Abstract

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 S42- at -1.1 to -0.1 V (vs Ag/AgCl), S8 from -0.3 V, and S52- and S62- 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.