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

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 similar to 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.