Modulating Photovoltaic Conversion Efficiency of BiFeO₃-Based Ferroelectric Films by the Introduction of Electron Transport Layers

The sol–gel method exhibits the advantages of simple preparation, low cost, and easy control of stoichiometry, which is widely used for the fabrication of BiFeO3-based perovskite ferroelectric films. However, because of the volatilization of organic solvents during the annealing process, voids will inevitably be formed. In this article, high-quality BiFeO3-based thin films (with or without La doping) were prepared by physical vapor deposition methods, namely as magnetron sputtering and pulsed laser deposition, respectively. The deposition procedure of gas particles and the annealing process of thin films could be performed simultaneously by pulsed laser deposition, while is impossible by magnetron sputtering. As a result, pulsed laser deposition is considered as a more suitable approach for ferroelectric thin films fabrication. Besides the adoption of the pulsed laser deposition approach for the fabrication of highly dense thin films, the integration of electron transport layers (SnO2, TiO2, and ZnO) and La3+ doping is demonstrated to help to alleviate the problem of high electron–hole recombination rate, which then increases the photovoltaic conversion efficiency. In this contribution, planar solar cells, which were fabricated by the pulsed laser deposition approach with TiO2 as the electron transport layer, exhibited the best efficiency of 5.62% with a reduced leakage current density. This work provides a promising paradigm for the further development of high-performance BiFeO3-based perovskite solar cells through the modulation of fabrication process and introduction of electron transport layers.