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 SnO₂ nanoparticle underlayer and a ZnO nanorod overlayer was prepared and its photovoltaic performance was compared to photoanodes consisting of SnO₂ 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/cm² and an open-circuit voltage (V_OC) of 500 mV. The photoanode with SnO₂ nanoparticle only exhibited higher PCE (1.24%) because of higher J_SC (6.64 mA/cm²), whereas V_OC (340 mV) was lower than ZnO nanorod. Compared to SnO₂ nanoparticle and ZnO nanorod films, the bilayer structured film demonstrated much higher PCE (2.62%) because of both higher J_SC (7.35 mA/cm²) and V_OC (660 mV). Introduction of ZnO nanorod on the SnO₂ 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 SnO₂ film was mainly responsible for the improved efficiency.