Preparation And Study Of Self-Powered PEDOT:PSS/α-Ga₂O₃/FTO Solar-Blind Ultraiolet Detector

Solar blind ultraviolet detection technology has attracted much attention of researchers because of its strong anti-interference ability and high sensitivity.Ga₂O₃ has been widely studied because of its suitable band gap（4.8-5.61 e V）,no need of alloying and simple preparation.Most Ga₂O₃-based detectors require power supply.Therefore,a self-powered solar-blind ultraviolet（UV）detector without external bias is becoming one of the research hotspots.Among most Ga₂O₃-based self-powered typed detectors,the replacement of metal and other semiconductors with organic compounds has become a new research direction to realize self-powered detectors through organic-inorganic heterojunction,owing to which have the advantages of solvable growth and spin-coating.PEDOT:PSS aqueous solution can be conveniently applied directly through the spin-coating process,showing the advantages of lower price and simpler preparation process.Moreover,PEDOT:PSS can also form organic-inorganic rectifying heterojunction with Ga₂O₃ to realize self-power detection.However,at present,most of Ga₂O₃-based solar-blind ultraviolet detectors are based onβ-Ga₂O₃,during whose growth or transformation high temperature environment should be provided.In contrast,α-Ga₂O₃ is also easy to be prepared by a simple process such as hydrothermal method,and has a high photoelectric conversion efficiency in the solar-blind ultraviolet region.Therefore,choosing PEDOT:PSS andα-Ga₂O₃ as heterojunction to realize self-powered detection can promote the development of Ga₂O₃ solar-based blind ultraviolet detectors in the direction of energy-saving,environmental protection and low cost.In this paper,theα-Ga₂O₃ nanowire arrays were prepared by simple hydrothermal method and annealing method,and PEDOT:PSS/α-Ga₂O₃/heterojunction were also prepared by spin-coating method.And the material properties and self-powered properties of photodetectors were investigated in details.The main contents are as follows:（1）Ga OOH was prepared by hydrothermal method using gallium nitrate as reaction source and FTO as substrate,which was transformed intoα-Ga₂O₃ by thermal annealing at550°C.The optical band gap ofα-Ga₂O₃ is about 5 e V.Luminescence of donor-acceptor pair at 3.18 e V was observed in PL spectra.As a common defect,V_O plays an important role in defect luminescence.In the analysis of high-precision XPS spectra of O1s,we observed the characteristic peak of V_O at 532.7 e V,which confirmed the existence of V_O.（2）PEDOT:PSS/α-Ga₂O₃/FTO heterojunction was prepared by spin-coating technique.α-Ga₂O₃ was coated by PEDOT:PSS with a thickness of 70-100 nm.The optical band gap of the heterojunction is about 4.9 e V,similar to that ofα-Ga₂O₃,which indicates PEDOT:PSS has little effect on the band gap of the heterojunction.Both PEDOT:PSS andα-Ga₂O₃ characteristic peaks were observed by Raman measurement,which not only indicates that PEDOT:PSS has high crystal quality,but also indicates that PEDOT:PSS has no effect on the crystal structure ofα-Ga₂O₃.（3）We studied the self-powered characteristics of PEDOT:PSS/α-Ga₂O₃/FTO detector.The rectifying ratio of the device can be up to 63（±2 V）.At 0 V,the peak response of the detector is 1.0’10^-3A·W^-1（245 nm）,which is more than four orders of magnitude higher than that of theα-Ga₂O₃/FTO device,and the UV-visual rejection ratio is 1288.However,the detector has a long decay time of 0.198 s,which may be related to the prolonged hole lifetime due to the capture of defects such as V_O.（4）The self-powered mechanism of PEDOT:PSS/α-Ga₂O₃/FTO detector was described in details by energy band diagram.Theα-Ga₂O₃/FTO heterojunction has low barrier and weak internal electric field,so it cannot realize obvious rectifying effect.Therefore,the obvious rectifying characteristics of PEDOT:PSS/α-Ga₂O₃/FTO devices come from PEDOT:PSS/α-Ga₂O₃ heterojunction interface,which also shows that the barrier height and the internal electric field of PEDOT:PSS/α-Ga₂O₃ heterojunction interface is higher than those ofα-Ga₂O₃/FTO interface.Thus,photocarries can be generated and separated at PEDOT:PSS/α-Ga₂O₃ heterojunction interface under 0 V and UV irradiation.Forα-Ga₂O₃/FTO device,phtoresponse can only be realized when UV light passes throughα-Ga₂O₃nanowire arrays to reachα-Ga₂O₃/FTO interface.Therefore,efficient self-powered properties can be demonstrated by the formation of PEDOT:PSS/α-Ga₂O₃heterojunctions at the surface ofα-Ga₂O₃/FTO.