Microsphere Light-Scattering Layer Assembled by ZnO Nanosheets for the Construction of High Efficiency (>5%) Quantum Dots Sensitized Solar Cells

This work reported on a bilayer photoelectrode constructed by ZnO nanoparticle (NP) film and ZnO microsphere (MS) scattering layer for CdS/CdSe quantum dot cosensitized solar cells (QDSCs) with a power conversion efficiency (PCE) of greater than 5%. We controlled the growth orientations of ZnO crystals to form nanosheets, which attached together and assembled into MS due to the high surface energy of the nanosheets. MSs were used as a top layer to effectively increase the light diffuse reflection and harvesting to enhance photogenerated current. In comparison with ZnO NPs photoelectrode, the short circuit current density (J(sc)) of ZnO NPs/MSs photoelectrode increased from 10.3 mA/cm(2) to 16.0 mA/cm(2), which was an enhancement of 55%. To further increase the fill factor and PCE of QDSCs, ZnO NPs/MSs was treated in the solution of H3BO3 and (NH4)(2)TiF6 to form a barrier surface layer, which suppressed the charge recombination and prolonged electron lifetime. As a result, the solar cell displayed J(sc) of 17.13 mA/cm(2), V-oc of 0.56 V, FF of 0.53, and PCE of 5.08%, one of the highest values for ZnO-based QDSCs at this time.