Enhanced photovoltaic behavior of thickness-dependent BiFeO₃-based heterostructures via the introduction of electron transport layers

Thickness and direct band gap are two important parameters affecting the photovoltaic performance of BiFeO₃ (BFO)-based thin film. In this paper, thickness effects on the microstructure and insulating properties of BFO thin film are firstly explored. The minimum leakage current density (2.18 × 10^− 5 A/cm² at 200 kV/cm) of 200 nm thin film is obtained due to a well-crystallized polycrystalline structure with high densification. On the basis, FTO/TiO₂/BFO and FTO/ZnO/BFO heterostructures are proposed and successfully prepared. It turns out that with the introduction of TiO₂ and ZnO acting as electron transport layer, both heterostructures possess enhanced absorption intensity and exhibit a significant red-shift, which can be ascribed to the reduced direct band gap (E_g) of 2.66 and 2.63 eV, respectively. Particularly, ZnO/BFO possess enhanced photovoltaic with relatively large V_oc, J_sc, FF and η values of 1.32 V, 3.63 mA/cm², 0.59 and 2.86, respectively. Our results demonstrate that the introduction of electron transport layer tends to be an effective way in improving the photovoltaic performance of BFO-based films.