Efficiency enhancement of PbS quantum dots-sensitized nanocrystalline SnO2 thin film prepared by two-phase method

A novel two-phase method was employed to directly deposit PbS quantum dots (QDs) on nanocrystalline SnO 2 thin films. In the two-phase method, the nanocrystalline SnO 2 thin film with adsorption of Pb 2+ ions was placed in an aqueous solution, and S 2− ions were dissolved in an oil solution. As two solutions were contacted, S 2− ions prefer to transfer to the aqueous solution and diffuse to the thin film surface with the adsorbed Pb 2+ ions to homogeneously form monodispersed PbS QDs on the nanocrystalline thin film. The homogeneous monodispersed QDs-sensitized thin film was used as a photoelectrode to fabricate QDs-sensitized solar cell. The loaded amount of PbS QDs and the thickness of ZnS passivation layer were optimized to obtain the highest light-to-electric conversion efficiency of 1.01 % under the simulated AM 1.5 illumination, which is increased by 61 % compared with that of the PbS QDs-sensitized solar cell employing the successive ionic layer adsorption and reaction (SILAR). The solar cell with homogeneous sensitization of QDs generates a photocurrent density of 11.09 mA·cm −2 , which is 2.4 times higher than that of the unhomogeneous one prepared by SILAR. The conversion efficiency enhancement mechanism due to the two-phase method was discussed in detail through the measurements of intensity-modulated photovoltage spectrum and electrochemical impedance spectroscopy.