Regenerative PbS and CdS Quantum Dot Sensitized Solar Cells with a Cobalt Complex as Hole Mediator

Abstract

Metal sulfide (PbS and CdS) quantum dots (QDs) were prepared over mesoporous TiO₂ films by improved successive ionic layer adsorption and reaction (SILAR) processes. The as-prepared QD-sensitized electrodes were combined with a cobalt complex redox couple [Co(o-phen)₃]^2+/3+ to make a regenerative liquid-type photovoltaic cell. The optimized PbS QD-sensitized solar cells exhibited promising incident photon-to-current conversion efficiency (IPCE) of over 50% and an overall conversion efficiency of 2% at 0.1 sun in a regenerative mode. The overall photovoltaic performance of the PbS QD-sensitized cells was observed to be dependent on the final turn of the SILAR process, giving a better result when the final deposition was Pb²⁺, not S^2-. However, in the case of CdS QD-sensitized cells, S^2- termination was better than that of Cd²⁺. The cobalt complex herein used as a regenerative redox couple was found to be more efficient in generating photocurrents from PbS QD cells than the typical hole scavenger Na₂S in a three-electrode configuration. The CdS-sensitized cell with this redox mediator also showed better defined current−voltage curves and an IPCE reaching 40%.