Design,Fabrication And Investigation Of The Interface Effect Of CH₃NH₃PbCl₃/ZnO Ultraviolet Detector

Recently,ultraviolet detection technology has been widely used in civil and military fields such as detection of ozonosphere hole,flame warning,missile early warning and so on.As the main part of ultraviolet detection technology,the preparation and research of high-performance ultraviolet detectors has become a major research focus.The optical band gap of CH₃NH₃PbCl₃ material is about 3.1 eV,corresponding to ultraviolet.As an organic-inorganic perovskite material,CH₃NH₃PbCl₃ material has the advantages of high carrier mobility,long carrier diffusion distance and high optical absorption,which makes it very suitable for ultraviolet detection.Photodetectors with different device structures have been fabricated using organic-inorganic perovskite materials with different material structures,such as bulk single crystals,thin films and nanostructures.These devices have shown good performance.Although a series of significant advances have been made in the field of organic-inorganic perovskite photodetection,there are still some problems:organic-inorganic perovskite materials are very sensitive to the preparation environment,resulting in different properties of organic-inorganic perovskite devices prepared under different preparation conditions.In addition,organic-inorganic perovskite devices can react with water molecules in the air,leading to rapid deterioration in ambient air.Recently,it has been found that the combination of organic-inorganic perovskite materials and inorganic semiconductors can effectively improve the performance and stability of organic-inorganic photodetectors.However,the enhancement mechanism is still not very clear.In addition,this method has not been applied in the field of organic-inorganic perovskite ultraviolet detectors.ZnO materials have good application prospects in the field of ultraviolet detection due to its continuous adjustable detection range from visible blindness to solar blindness,high electron saturation rate,abundant raw materials and environment-friendly characteristics.Therefore,high performance organic-inorganic heterostructure ultraviolet detectors can be obtained by combining CH₃NH₃PbCl₃ with ZnO.According to the above ideas,this paper has carried out relevant research and achieved a series of phased results,the main results are shown as follows:1.High quality ZnO thin films are the basis of preparing high performance CH₃NH₃PbCl₃/ZnO composite ultraviolet detectors.Therefore,high quality ZnO thin films were grown on C-face sapphire by MBE.The effects of air annealing,O₂annealing and O-beam irradiation on dark current of ZnO films were investigated.These post-processing methods have reduced the O vacancy defects on the surface of ZnO films,leading to reduce the dark current.In addition,by optimizing the growth conditions of ZnO thin films,i.e.reducing the beam current of Zn source,the dark current of ZnO films can be reduced significantly.The results have shown that this optimization method can effectively reduce the O vacancy defects in ZnO films.Then we annealed the optimized grown ZnO films in air and O₂ atomsphere.When the optimized grown ZnO films were annealed at 900 C in the O₂ atomsphere,the dark current was 3.16?A at 10 V bias.Compared with the unoptimized and post-treated ZnO films,the dark current was reduced by three orders of magnitude.2.CH₃NH₃PbCl₃/ZnO UV detector with vertical structure was first fabricated by combining the optimized and treated ZnO films with CH₃NH₃PbCl₃.The effects of different preparation methods of CH₃NH₃PbCl₃ and different substrates were studied.It is found that CH₃NH₃PbCl₃ film on ZnO has smoother surface morphology and better lattice quality.By testing CH₃NH₃PbCl₃/ZnO UV detector‘s dark current and photocurrent,responsivity,I-t curve and stability,we found that compared with pure ZnO and pure CH₃NH₃PbCl₃ UV detectors,CH₃NH₃PbCl₃/ZnO UV detector was enhanced in dark current,responsivity and response speed.The peak response of CH₃NH₃PbCl₃/ZnO UV detector at 1 V bias?365 nm?was about 1.47 A/W,and the decline time?90%-10%?was about 1.2 s.More interestingly,CH₃NH₃PbCl₃/ZnO UV detectors showed better air stability than pure CH₃NH₃PbCl₃ UV detectors.3.Then we use transient absorption spectroscopy to study the photogenerated carrier dynamics of pure ZnO film,pure CH₃NH₃PbCl₃ film and CH₃NH₃PbCl₃/ZnO composite film in detail.Through the comprehensive analysis of the static absorption spectra and static photoluminescence spectra of these films,it is found that under ultraviolet irradiation,the photogenerated electron transfer from CH₃NH₃PbCl₃ film to ZnO film in the CH₃NH₃PbCl₃/ZnO composite film,which makes the near-band-edge luminescence of ZnO in CH₃NH₃PbCl₃/ZnO composite film obviously enhanced compared with pure ZnO thin film.The optical properties of CH₃NH₃PbCl₃/ZnO composite film and the electrical properties of its ultraviolet detectors were comprehensively analyzed.The significantly improved performance of CH₃NH₃PbCl₃/ZnO UV detector is mainly attributed to the higher crystal quality of CH₃NH₃PbCl₃ on ZnO and the efficient carries'separation and transfer at the CH₃NH₃PbCl₃/ZnO interface.Our work provides an effective preparation method and relatively complete physical image of high-performance and stable organic-inorganic perovskite photodetectors.