Preparation of monodispersed PbS quantum dots on nanoporous semiconductor thin film by two-phase method

The novel two-phase method was developed to in situ prepare monodispersed PbS quantum dots (QDs) on nanoporous semiconductor thin film. In this method, the two phases refer to an oil phase consisting of S2− ions (phase I) and an aqueous solution (phase II). Nanoporous SnO2 thin film adsorbed by Pb2+ ions was immersed in the aqueous solution. The S2− ions contained in the oil phase prefered to transfer through the oil/aqueous interfaces, and contacted with Pb2+ ions on the nanoporous thin film within the phase II to form QDs. The particle size and size distribution of QDs were controlled by the diffusion of S2− ions within the phase II. Volume ratio of ethylene glycol and water in the phase II can change the diffusion rate of S2− ions in the phase II, thus PbS QDs with different particle sizes and size distribution were prepared. The SnO2 thin film with PbS QDs deposited by the two-phase method was used to fabricate QDs-sensitized solar cells and the corresponding photoelectric conversion efficiency attained to 1.05% measured under simulated illumination with intensity of 100 mW cm−2 (AM 1.5). These results demonstrated that the reported two-phase method is a facile and environment-friendly approach to fabricate monodispersed PbS QDs on the nanoporous SnO2 thin film.