Hierarchical SnO₂ nanoparticle-ZnO nanorod photoanode for improving transport and life time of photoinjected electrons in dye-sensitized solar cell.

A hierarchical photoanode comprising a SnO(2) nanoparticle underlayer and a ZnO nanorod overlayer was prepared and its photovoltaic performance was compared to photoanodes consisting of SnO(2) nanoparticle only and ZnO nanorod only. The photoanode layer thickness was adjusted to about 7.6 μm to eliminate thickness effect. Ruthenium complex, coded N719, was used as a sensitizer. The photoanode composed of ZnO nanorod only showed a power conversion efficiency (PCE) as low as 0.54% with a short-circuit photocurrent density (J(SC)) of 2.04 mA/cm(2) and an open-circuit voltage (V(OC)) of 500 mV. The photoanode with SnO(2) nanoparticle only exhibited higher PCE (1.24%) because of higher J(SC) (6.64 mA/cm(2)), whereas V(OC) (340 mV) was lower than ZnO nanorod. Compared to SnO(2) nanoparticle and ZnO nanorod films, the bilayer structured film demonstrated much higher PCE (2.62%) because of both higher J(SC) (7.35 mA/cm(2)) and V(OC) (660 mV). Introduction of ZnO nanorod on the SnO(2) nanoparticle layer improved significantly electron transport and lifetime compared to the SnO(2) only film. One Order of magnitude slower charge recombination rate for the bilayer film than for the SnO(2) film was mainly responsible for the improved efficiency.