Stress-mediated solution deposition method to stabilize ferroelectric BiFe1-xCrxO3 perovskite thin films with narrow bandgaps

Ferroelectric oxides with low bandgaps are mainly based on the BiFeO₃ perovskite upon the partial substitution of iron with different cations. However, the structural stability of many of these perovskites is only possible by their processing at high pressures (HP, >1GPa) and high temperatures (HT, >700ºC). Preparation methods under these severe conditions are accessible to powders and bulk ceramics. However, transferring these conditions to the fabrication of thin films is a challenge, thus limiting their use in applications. Here, a chemical solution deposition method is devised, which overcomes many of these restrictions. It is based on the application of an external compressive-stress to the film sample during the thermal treatment required for the film crystallization, promoting the formation and stabilization of these HP perovskites. We demonstrate the concept on BiFe_1-xCr_xO₃ (BFCO) thin films deposited on SrTiO₃ (STO) substrates and with large chromium contents. The resulting BFCO perovskite films show narrow bandgaps (Eg～2.57 eV) and an excellent ferroelectric response (remnant polarization, P_R～ 40 μC cm^?2). The polarized thin films under illumination present a large out-put power of ～6.4 μW cm^?2, demonstrating their potential for using in self-powered multifunctional devices. This stress-mediated solution deposition method can be extended to other perovskite films which are unviable under conventional deposition methods.