Minimizing the charge recombination rate at the FTO/Zn₂SnO₄ interface by metal oxide semiconductors in DSSCs

Charge recombination at interfaces is one of the main factors that limit the power conversion efficiency of dye-sensitized solar cells. In this work, to reduce the charge recombination at the transparent conductive oxide/mesoporous Zn₂SnO₄ interface and then to improve the photovoltaic performance, different types of metal oxide semiconductor thin films (including SnO₂, TiO₂ and ZnO) are deposited on the FTO substrate by thermal evaporation method. The results reveal that in comparison with SnO₂ and ZnO, the TiO₂ dense layer acts as the most appropriate blocking layer for suppressing the charge recombination and increasing the short-circuit current density and power conversion efficiency of the fabricated device. Furthermore, because of the formation of energy barrier at the FTO/Zn₂SnO₄ interface, the charge recombination rate is minimized and the injected electrons from the excited dye molecules into the conduction band of Zn₂SnO₄ are accumulated in its conduction band which leads to upward shift of the Fermi level and increases open-circuit voltage. The maximum power conversion efficiency of 3.02% with short-circuit current density of 7.36 mA/cm² and open-circuit voltage of 664 mV is obtained for the device comprising TiO₂ blocking layer.