Interface Engineering in All-Oxide Photovoltaic Devices Based on Photoferroelectric BiFe_0.9Co_0.1O₃ Thin Films

Photoferroelectric BiFeO₃ (BFO) has attracted renewed interest to be integrated into thin film photovoltaic (PV) devices as a stable, lead-free, and versatile photoabsorber with simplified architecture. While significant efforts have been dedicated toward the exploration of strategies to tailor the properties of this photoabsorber to improve the device performance, efficiencies still remain low. The modification of the BFO interface by the incorporation of transport-selective layers can offer fresh opportunities to modify the properties of the device. Identifying an optical and electrically suitable selective layer while ensuring easy device processing and controlled film properties is challenging. In this work, we determine the influence of incorporating a ZnO layer on the ferroelectric and photoresponse behavior of an epitaxial BiFe_0.9Co_0.1O₃ (BFCO)-based heterostructure. The device is completed with Sn-doped In₂O₃ (ITO) and La_0.7Sr_0.3MnO₃ (LSMO) electrodes. This all-oxide system is stable under ambient conditions and displays robust ferroelectricity. The coupled ferroelectricity-photoresponse measurements demonstrate that the short circuit current can be modulated by ferroelectric polarization in up to 68% under blue monochromatic light. Also, the responsivity of the system with the ZnO-modified interface is larger than that of the system with no ZnO. Complementary band energy alignment studies reveal that the observed increase in the short circuit current density of the device with ZnO is attributed to lower Fermi level energy at the ZnO/BFCO interface compared to the ITO/BFCO interface, which reduces charge recombination. Therefore, this study provides useful insights into the role of the ZnO interface layer in stable BFO-based devices to further explore their viability for potential optoelectronic applications.