Piezoelectricity-enhanced multifunctional applications of hydrothermally-grown p-BiFeO₃–n-ZnO heterojunction films

This paper reports the fabrication of p-BiFeO₃ (BFO)–n-ZnO composite films on tin-doped indium oxide substrates through a facile hydrothermal method and the tuning of various functional properties of single-crystalline BFO and ZnO for piezoelectricity-enhanced multiapplications. BFO microplates were embedded in ZnO nanorod arrays; the clear interfaces indicated the robust formation of the heterojunction, which was also confirmed through X-ray photoelectron spectroscopy. The conductivity type of the BFO and ZnO was determined through Mott–Schottky, open-circuit potential, and photoelectrochemical measurements. Moreover, the induced piezopotential distributions of the samples were theoretically simulated, and the piezotronics, piezophototronics, and Schottky behavior of the composites were determined. The composite-based piezoelectric nanogenerators exhibited durable output and excellent sensitivity, enabling practical sensor applications. Excellent piezophotodegradation with a rate constant of approximately 3 × 10⁻² min⁻¹ for the composite was attributable to predominant ·O₂⁻ radicals. The maximum applied bias photon-to-current efficiency and piezophotoelectrochemical current density were approximately 0.86% (at 0.63 V vs. Ag/AgCl) and 1.4 mA cm⁻², respectively. The multiapplications of the p–n junction composites were primarily attributable to the enhanced piezoelectric coefficient (d₃₃ ≈ 27.3 pm·V⁻¹), favorable electrochemical surface area (≈69.8 mF cm⁻² mg⁻¹), prolonged charge carrier lifetime, weak photoluminescence, and suitable band positions and piezopotential-induced band bending.