The role of crystallinity of the Nb2O5 blocking layer on the performance of dye-sensitized solar cells

Abstract

The prevention of back electron transfer by inserting an energy barrier layer at the interface of a photo-anode is an effective method for improving the photovoltaic parameters in dye sensitised solar cells (DSSCs). In this study, phase a modified Nb₂O₅ blocking layer was inserted at the fluorine doped tin oxide (FTO)/TiO₂ interface via a Rf magnetron sputtering process. For a critical tunnelling distance of ∼40 nm, the crystalline Nb₂O₅ blocking layer improved the efficiency close to 7% and outperformed the amorphous blocking layer by about 68%. The longer electron lifetime observed in DSSCs containing an inhomogeneous Nb₂O₅ layer indicates that trapping/de-trapping impedes the discharge of electrons to the TiO₂ band edge. The origin of the longer electron lifetime is explained by formulating a theory from photovoltage decay measurements.