Lead-Sulfide-Selenide Quantum Dots and Gold-Copper Alloy nanoparticles Augment Light Harvesting of Solar Cells

Lead-sulfide-selenide (PbSSe) quantum dots (QDs) and gold-copper (AuCu) alloy nanoparticles (NPs) are incorporated in a cadmium sulfide (CdS)/titanium oxide (TiO2) photoanode for the first time for enhanced conversion of solar energy to electricity. PbSSe QDs with a band gap of 1.02 eV, extend the light harvesting range of the photoanode from visible to the near infrared region. The conduction band (CB) edge of PbSSe QDs is wedged between the CBs of TiO2 and CdS; this additional level coupled with a good electrical conductivity of the dots facilitate charge transport and collection, for a high power conversion efficiency (PCE) of 4.44% is achieved for the champion cell with the TiO2/PbSSe/CdS electrode. Upon including AuCu alloy NPs in the QDs sensitized electrodes, they enhance light absorption via plasmonic and light scattering effects and also by injection of hot electrons to the CBs of the QDs. Incident photon to current conversion efficiency (IPCE) enhancement factor comparisons, fluorescence decay and impedance studies reveal that PbSSe QDs and AuCu alloy NPs, promote charge injection to the current collector, and increase the photogenerated charges produced, thus enabling the TiO2/PbSSe/CdS/AuCu cell to deliver the highest PCE of 5.26%, among the various photoanode compositions used