Performance And Application Of Ultraviolet-Blue Dual-Band Bi₂O₃/TiO₂ Self-Powered Photodetectors

Photodetectors（PDs）that convert optical signals into measurable voltage,current and resistance signals for information transfer are the basis for optoelectronic information systems and the Internet of things.Diversified targets,complex environments,and diverse tasks have created new demands for the development of photodetectors.Dual-band PDs without external bias driving can achieve the detection of targets in complex environments,which can be widely used in imaging technology,optical wave communication,optical waveguide technology and environmental monitoring.Dual-band self-powered PDs can be constructed using heterojunctions with photovoltaic effect,but the performance of devices still needs to be further improved to meet the development needs in multiple fields.Bi₂O₃ attracts attention due to its tunable band gap,high dielectric constant and high O^2-conductivity.Performance of PDs is closely related to the crystal structure and energy band structure of heterojunctions.In this paper,p-n junction PDs with Bi₂O₃ nanosheets and TiO₂nanorod arrays（NRs）are constructed,and self-powered photoresponse properties modulated by Bi₂O₃ phase structure and crystalline quality,and the photoresponsive properties of the UV-blue dual-band for applications in light-controlled logic and two-color imaging.The main contents are as follows:（1）Self-powered photoresponse characteristics of Bi₂O₃/TiO₂ heterojunction.The energy band structure,density of states,and absorption and reflection spectra of different crystalline surfaces ofβ-Bi₂O₃ are calculated by first-principles calculation,and the electronic structure and optical properties ofβ-Bi₂O₃ are analyzed.β-Bi₂O₃/TiO₂ PD prepared by a two-step hydrothermal method exhibits UV-blue dual-band photoresponse at a bias voltage of 0 V,with a responsivity of 1.2 m A/W,detectivity of 2.5×10¹⁰ Jones,and sensitivity of 3.5×10² under UV illumination.The feasibility of dual-band self-powered TiO₂/Bi₂O₃ PD with the photovoltaic-type p-n junctions is verified by a combination of theory and experiment.（2）Modulation ofβ-Bi₂O₃ crystalline quality and energy band structure to enhance the self-powered photoresponse of Bi₂O₃/TiO₂ PDs.Chemical bath deposition（CBD）and hydrothermal preparation are used to prepareβ-Bi₂O₃ and TiO₂,respectively and the nucleation and growth processes of Bi₂O₃ films are regulated by changing the concentration of triethanolamine（TEA）complexing agent,which in turn regulates the morphology of Bi₂O₃ films.The constructed self-powered Bi₂O₃/TiO₂ PD with TEA concentration of 0.3M exhibits optimal performance,with a responsivity of 1.79 m A/W,detectivity of 5.94×10¹⁰ Jones,and sensitivity of 1.3×10³ under UV illumination.The excellent device characteristics are mainly related to the larger built-in electric field at the interface heterojunction and small interfacial transfer resistance.The Bi₂O₃/TiO₂device has been used to explore the application of optical control"AND"gate logic utilizing UV-blue dual-band photoresponse characteristics of Bi₂O₃/TiO₂ devices,indicating that the device has the potential application in UV-encrypted visible light transmission.（3）Regulation of Bi₂O₃ phase structures to enhance the self-powered photoresponse of Bi₂O₃/TiO₂ PDs.β-Bi₂O₃ andα-Bi₂O₃ have different crystal and energy band structures,and the ratio ofβ-Bi₂O₃ andα-Bi₂O₃ is modulated by changing the annealing temperatures,and pureβ-Bi₂O₃ andα-Bi₂O₃ are obtained by annealing at350℃ and 500℃,respectively.β-Bi₂O₃ andα-Bi₂O₃ are calculated by the first principles.The energy band structure,density of states,and effective mass ofβ-Bi₂O₃andα-Bi₂O₃ are calculated,and the differences in energy band structure,optical properties,and electrical properties of the two phase structures of Bi₂O₃ are analyzed theoretically.β-Bi₂O₃/TiO₂ device presents excellent UV-blue dual-band self-powered photoresponse characteristics due to the larger heterojunction built-in electric field,smaller interfacial transfer resistance and longer carrier lifetime,as well as the larger mobility ofβ-Bi₂O₃,having a responsivity of 26.7 m A/W,detectivity of 5.93×10¹¹Jones and sensitivity of 8.9×10³ under UV illumination.The UV-blue dual-band photoresponse characteristics of the PDs are exploited to the application in dual-color imaging system,which can achieve online monitoring of targets.