A novel anion-exchange strategy for constructing high performance PbS quantum dot-sensitized solar cells

Near-infrared responsive PbS quantum dots (QDs) have received particular attention serving as promising candidates for next generation photovoltaics. This work explores a novel anion-exchange strategy to produce high quality in-situ grown PbS QDs on mesoporous TiO2 films. Such an anion-exchange reaction occurs between PbSO3 and S2- in aqueous solution at low temperature under ambient conditions. A solar cell based on such anion-exchanged PbS QDs yields an impressive power conversion efficiency of 3.06% without resorting to any doping or co-sensitization, achieving around 200% performance improvement with respect to that of a conventional successive ionic layer adsorption and reaction (SILAR) processed device. Based on detailed microscopic, optical and electrochemical characterizations, much enhanced photovoltaic performance is attributed to improved electron injection and collection efficiencies. Up-shifted conduction band level of reasonable small-sized PbS QDs processed by anion-exchange gives rise to desired electron injection from PbS to TiO2, while simultaneous deposition of ZnS passivation layer along with the formation of anion-exchanged PbS QDs allows the minimization of interface states for reduced charge recombination. This work offers an alternative promising approach for constructing high performance PbS QD-sensitized solar cells.