| All-inorganic halide perovskite materials are intensively studied for applications of photodetection,solar cells,light-emitting diodes,high-energy particle detection and other fields due to their tunable band gap,excellent light absorption,high carrier mobility and fluorescence yield.However,it is still a challenge to prepare large-area pinhole-free uniform films with good crystallinity by the wet chemical methods owing to the poor solubility of the precursors,the low crystallization temperature and the complex crystal structures.The perovskite films always suffer from some problems such as high defect density,poor coverage,and dense grain boundarie.To satisfy the needs of applications,the quality of the films as well as the device structure should be improved,making the device more stable and efficient.In this dissertation,based on the main line of depositing high-quality films,van der Waals epitaxial growth of the CsPbBr3 films has been achieved.On this basis,detector arrays with weak light detection and imaging capabilities,as well as flexible detectors with good weather resistance and photoelectric response,have been prepared through process optimization and structural design.The main results in this dissertation are given below:1.High quality CsPbBr3 film for MSM type flexible photodetector:A van der Waals epitaxial all inorganic halide perovskite CsPbBr3 film is prepared on a flexible muscovite substrate by PLD.AFM,XRD and TEM characterization methods show that this CsPbBr3 film exhibits excellent lattice structure and a flat surface.The absorption spectrum and photoluminescence spectrum of the film are consistent with those reported in other literatures,and fully accord with the optical characteristics of high-quality CsPbBr3 films.Based on this film.a flexible MSM photoconductive detector was fabricated.The detector showed an ultra-fast response speed,with a turn-on time and recovery time of 42.16μs/44.88μs.The on-off ratio of the detector reached 1.1 × 105,and the responsivity and specific detection rate were 0.168 A/W and 2.41 ×1014 Jones,showing high photosensitivity.More importantly,the detector exhibited excellent mechanical stability and environmental stability.This work provides a feasible synthetic strategy for growing high quality perovskite films and elucidates the key factors that may affect the performance and stability of perovskite-based optoelectronic devices.2.Flexible self-powered weak light detectors based on ZnO/CsPbBr3/γ-CuI heterojunction:Using PLD and high vacuum thermal evaporation,a sandwich-structured ZnO/CsPbBr3/CuI heterojunction is fabricated under vacuum conditions.Flexible self-powered photodetectors were fabricated based on this ZnO/CsPbBr3/CuI heterojunction.XRD characterization shows that both the CsPbBr3 film and the ZnO film have a preferred(001)orientation,and the CuI film is γ phase.We also deposite ZnO,CsPbBr3,and Cul single films on the ITO/PET substrates,respectively,and measure the absorption and photoluminescence spectra of each film,which are consistent with literature reports.Through comparing the work functions of the three materials,the heterojunction interfaces between them are all second-type contacts,and the photogenerated carriers can be rapidly separated by the built-in potential and transported to the electrodes to form a response photocurrent.Benefitting from the good crystallization of the films,the detector exhibits excellent detecting performance.In self-powered mode,the photoresponsivity of the detector reaches 140 mA/W and the specific detection rate is 8.1 ×1013 Jones.Due to the high carrier mobility and short carrier lifetime in the CsPbBr3 film,the detector has an extremely fast response capability with a response time of 3.9μs/1.8μs.More importantly,the unpackaged device has excellent stability.During continuous operation for 7000s,the performance does not deteriorate,and the performance decreases only slightly after 1 00 times of bending.After being placed in an indoor environment for 21 days,the photocurrent will drop to 75%of the initial value.The detector array obtains spot images with clear and sharp edges in an extremely short imaging time,proving its excellent fast imaging capability.This work provides a way to study the working principle of self-powered optoelectronic devices and explore high performance devices.3.Self-powered photodetector with excellent environmental stability:Improving the weatherability and stability of halide perovskite-based optoelectronic devices has always been the hottest topic in this field.The CsPbBr3 films prepared by PLD is dense with less defects and grain boundaries.Therefore,the films have better stability compared with those prepared by wet chemical methods.By using the amorphous rubrene film as the hole transport layer and the protective layer,the stability of the CsPbBr3 based self-powered photodetectors is greatly improved.Since the thickness of the rubrene film is only 200 nm,the mechanical stability of the device is also good.As shown by the performance characterizations,the highest responsivity of the detector can reach 77.2 mA/W,the detection rate is 2.61 ×1013 Jones,the signal-to-noise ratio is 17700,and the response time is 0.68 ms/0.92 ms,respectively.More importantly,under the protection of rubrene,the performance of the device shows only a 6%decrease after continuous operation for 15000 s,which is much better than that of the unprotected device.When the device is immersed in water,the CsPbBr3 film can still produce obvious green fluorescence under excitation light,which indicates that the device can be waterproof for a period of time.This work provides an approach for the design and fabrication of a flexible,selfpowered,highly sensitive and highly stable perovskite photodetector. |
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