Preparation And Photoelectrical Properties Study Of The Composites Material Of PbI₂ Nanosheets And CdSe Nanobelts

Lead iodide nanosheets（PbI₂ NSs）are two-dimensional（2D）materials with a band gap of 2.36e V and they have a good response in the visible light（450-510 nm）.They are often used as perovskite precursors.However,the spectral response range of PbI₂ NSs is narrow and the resistance is large.So there are few studies based on PbI₂NSs composites,which limit the further application of PbI₂ NSs.In order to solve above problems,2D cadmium selenide nanoribbons（CdSe NBs）were chosen as its composite materials in this study.CdSe has a band gap of 1.7 e V and it is one of the most widely studied II-VI semiconductor materials.Such a narrow band gap has a good response in the long wavelength of visible light,which can perfectly compensates for the spectral response of PbI₂ in the visible range.More importantly,CdSe has high carrier mobility and excellent photoelectric performance,which can effectively improve the photoelectric characteristics of PbI₂ NSs.Therefore,this thesis mainly prepared the PbI₂ NS/CdSe NB composite device,tested and analyzed the photoelectric performance of the device.Finally,the working principle of the device was discussed.The main research contents and results are summarized as follows:1.We prepared PbI₂ NSs and nanowires（NWs）in water and N,N-dimethyl ammonium（DMF）respectively.The morphology,phase and structure of PbI₂ NSs were characterized by SEM,XRD,XPS,UV-vis and Raman.Then PbI₂ NSs photoelectric device is designed and fabricated,and its photoelectric properties are studied.The photo-dark current ratio of PbI₂ NS is 383.8 times that of PbI₂ NWs by photo-dark current analysis.The spectral response range of PbI₂ NS device is from 450 nm to 510nm,and the maximum response is achieved at 490 nm.Moreover,the device response and quantum efficiency under 450 nm and 490 nm monochromatic light irradiation were compared,which further confirms that PbI₂ NSs are more sensitive to 490 nm monochromatic light.The I-t curve shows that PbI₂ NSs have good stability,and the rise and fall time has only 5 ms and 4.8 ms.2.CdSe NBs were prepared by physical vapor deposition.The morphology and crystal structure of CdSe NBs were characterized by SEM and TEM,which indicated that CdSe NBs was single crystal with uniform width and smooth surface.In addition,the structure and composition of CdSe NBs were characterized by EDX,XRD and XPS,and the results showed that CdSe NBs had good crystallicity and no excess impurities.Finally,Raman and PL were used to study the optical properties of CdSe NBs.3.The prepared single CdSe NB was dispersed on a single PbI₂ NS in a one-step method to make PbI₂NS/CdSe NB composite photoelectric device,and the photoelectric performance of the device was tested.It was found that the spectral response range was almost extended to the entire visible light range（about 350-750nm）.The photo-dark current ratio of PbI₂ NS/CdSe NB composite device reaches6.778×10³A,which is 3.87 times that of pure PbI₂ NSs device.In addition,the maximum response rate is 347.57A/W and the quantum efficiency is 88282.78%under490nm monochromatic light irradiation,which are respectively 28.4 and 26.1 times of pure devices of PbI₂NS.Next,the rise time and fall time were measured,which were5.3 and 7.3 ms respectively.The results showed that the PbI₂ NS/CdSe NB composite device not only extends the spectral response in the visible light range,but also promotes the separation of electron hole pairs,which improves the photoelectric performance.