The origin of enhanced optical absorption of the BiFeO3/ZnO heterojunction in the visible and terahertz regions

Highly Sensitive and Tunable Self-Powered UV Photodetectors Driven Jointly by p-n Junction and Ferroelectric Polarization

Ferroelectric (FE) materials are thought to be promising materials for self-powered ultraviolet (UV) photodetector applications because of their photovoltaic effects. However, FE-based photodetectors exhibited poor performance because of the weak photovoltaic effect of FE depolarization field (E_dp) on the separation of photo-generated carriers. In this work, self-powered photodetectors based on both E_dp and built-in electric field at the p-n junction (E_p-n) were designed to obtain enhanced device performance. A NiO/Pb_0.95La_0.05Zr_0.54Ti_0.46O₃ (PLZT) heterojunction-based device is constructed to take advantage of energy level alignments that favor electron extraction. The device exhibits a tunable performance upon varying the polarization direction of PLZT. The NiO/PLZT heterojunction-based device with the PLZT layer in the poling down state shows a higher responsivity [R = (1.8 ± 0.12) × 10^-4 A/W] and detectivity [D* = (3.69 ± 0.2) × 10⁹ Jones], a faster response speed (τ_r = 0.34 ± 0.03 s, τ_d = 0.36 ± 0.02 s), and a lower dark current [I_dark = (1.3 ± 0.19) × 10^-12 A] under zero bias than the PLZT-based device because of the synergistic effects of E_dp and E_p-n. Moreover, under weak-light illumination (0.1 mW/cm²), it exhibits even higher R [(6.3 ± 1.2) × 10^-4 A/W] and D* [(1.29 ± 0.26) × 10¹⁰ Jones] values, which surpass those of most previously reported FE-based self-powered photodetectors. Our work emphasizes the role of the coupling effect between E_p-n and E_dp in the photovoltaic process of NiO/PLZT heterojunction-based devices and provides an effective way to promote the self-powered UV photodetector applications.

Photodegradation of 2,4-dichlorophenol and rhodamine B over n-type ZnO/p-type BiFeO3 heterojunctions: detailed reaction pathway and mechanism

The development of new technologies for efficient degradation of pollutant has been an increasing demand in the globe due to the serious environmental issues. Herein, we report n-type ZnO/p-type BiFeO₃ composites as highly efficient visible light nanophotocatalysts prepared via a wet chemical solution method. Based on the measurements of ^•OH-related fluorescence (FL) spectra, photoluminescence (PL) spectra, photoelectrochemical I-V curves, and electrochemical impedance spectra (EIS), it is demonstrated that the photo-induced charge carrier (electron-hole pairs) in the as-prepared n-type ZnO/p-type BiFeO₃ composites with proper amount of the coupled ZnO (10% by mass) exhibits high separation compared with the bare BiFeO₃ (BFO) nanoparticles. This is well responsible for the superior visible light photocatalytic performance of the composites for 2,4-dichlorophenol (2,4-DCP) and rhodamine B (RhB) degradation. It is confirmed by means of scavenger test and liquid chromatography-tandem mass spectrometry (LC/MS) analysis of the intermediate products that ^•OH is the pre-dominant oxidant involved in the degradation of 2,4-DCP. A detailed reaction pathway for 2,4-dichlorophenol degradation over the amount-optimized ZnO/BFO composite is proposed mainly based on the LC/MS product ions. This work will provide a feasible route to design and develop BFO-based highly efficient visible light-active photocatalysts for environmental purification and could be extended to other visible light-active semiconductor materials.