Performance enhancement of quantum dot sensitized solar cells by adding electrolyte additives

Besides the relatively high redox potential of the adopted S2-/S-n(2-) polysulfide redox couple electrolyte, the parasitic charge recombination process is another significant factor that limits the open-circuit voltage and consequent power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we report a facile method to modify the polysulfide electrolyte with the addition of polyethylene glycol (PEG) additives to suppress the charge recombination occurring at the TiO2/QDs/electrolyte interfaces. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the PEG additive in the polysulfide electrolyte reduces interfacial recombination when compared with the conventional polysulfide electrolyte in the absence of the PEG additive. A dramatic enhancement of PCE from 5.80% to 6.74% was observed with the introduction of 15 wt% PEG in the polysulfide electrolyte in CdSe based QDSCs. Moreover, the PEG additive also improves the photovoltaic performance stability of the resultant cells.