Research On Photodetectors Based On Perovskite Single Crystals

Photodetector is a class of device that can directly convert optical signals into electrical signals,which plays a vital role in a variety of fields such as medical imaging,automated production and military detection.In the past decade,with the continuous development of automatic driving,environmental monitoring,optical communication,biosensors and other technologies,the demand for high-performance photodetectors has become increasingly prominent.In the past,virous types of semiconductor optoelectronic materials have been most widely used in photodetectors,such as silicon,the III-V compound semiconductors,organic polymers and colloidal quantum dots.However,the preparation of traditional inorganic semiconductor materials is always complex and expensive.The polymer and colloidal quantum dots with unmanageable synthesis have the disadvantages of insufficient absorption and short carrier lifetime,which severely limits their practical applications.In recent years,the emergence of perovskite materials has opened up another vibrant spring for the research of optoelectronic devices.Due to the special crystal and electronic structure,perovskite material AMX₃(A=organic or inorganic cation,M=metal cation,X=halogen anion)has unique and nearly perfect optoelectronic properties(such as tunable direct bandgap,high absorption coefficient,high carrier mobility and long diffusion length),therefore,it provides great potential for the development of solar cells,optically pumped lasers,light emitting diodes,field effect transistors and photodetectors.In particular,the solution-processed perovskite photodetector with low cost,high response,low dark current and wide detection range has aroused the research interest of many scientific researchers.However,most of the current perovskite-based photodetectors are mainly polycrystalline films,and grain boundary and crystal grain defects affect the lateral transport of carriers,making the performance of the devices far less than expected.Perovskite single crystal has negligible grain boundaries,low defect state density,and has potential advantages in stability and photoelectric properties.Therefore,it is of great significance to make full use of the advantages of perovskite single crystals to design high-performance photodetectors based on perovskite single crystal materials to meet the new development trends.However,in addition to the performance of the device,the internal physical mechanism and carrier dynamics process have always been the focus of attention.Therefore,whether a new characterization method can be found to monitor the internal charge dynamics of the device is also a major issue currently facing challenge.Based on the above research status and research purpose,this thesis mainly focusses on the performance improvement of bromo-based perovskite single crystal thin film photodetectors and the transmission mechanism of the internal carriers.The main research work of this dissertation is described as follows:1.The study of photo-responsive field effect transistor based on all inorganic perovskite Cs Pb Br₃ single crystal thin filmWe employed a solution method to synthesize all inorganic perovskite single crystal thin film with excellent optical properties and low defect state density on a silicon substrate with SiO₂ dielectric layer,and a bottom-gate top-contact photo-responsive field effect transistor was fabricated.At room temperature,the device exhibited ambipolar transmission characteristics,that is,the electron and hole mobilities are 0.40 cm²V^-1s^-1 and 0.34 cm²V^-1s^-1,respectively.Meanwhile,we found that the device also has special light-dependent characteristics,which is first reported in perovskite materials.The above-mentioned phenomenon is mainly attributed to the conversion between photoconductivity and photovoltaic effect.2.The study of photodetectors based on MAPb Br₃ single crystal thin film/graphene heterojunctionsTaking advantage of van der Waals force,we directly constructed MAPb Br₃ single crystal thin film/graphene van der Waals vertical heterojunction photodetector on monolayer graphene substrate by solution method.The photoelectric performances of the photodetector under 532 nm laser were measured and analyzed using semiconductor test systems comparing to the normal photodetector based on pure perovskite single crystal.Compared with pure perovskite single crystal thin film photodetectors,the responsivity,detectivity and gain of perovskite/graphene vertical heterojunction photodetectors were enhanced by an order magnitude.We have explored the mechanism of the significant enhancement characteristics from the three aspects of energy band structure,steady-state photoluminescence and ultrafast carrier dynamics.The results showed that the improvement of photoelectric performance is mainly due to the growth of carrier lifetime of high-quality perovskite single crystal and the effective extraction and transmission of free carriers by graphene.3.The study of charge transfer dynamic in two-dimensional perovskite photodetectors based on Raman spectroscopyWe developed a non-invasive and non-destructive surface-enhanced Raman scattering method to monitor the charge transfer process of 2D perovskite single crystals based photodetector.Taking 3,4,4,10-Perylenetetracarboxylic Dianhydride(PTCDA)as a marker on the surface of perovskite,the interfacial and internal charge transfer process can be clearly observed by the vibration mode change of the Raman spectra.In addition,the anisotropic transport along various crystallographic directions by the quantum confinement effect was observed and identified from the distinct differences in the Raman spectra.This method provides a reliable way for comprehensive investigation of the carrier transport mechanism of 2D perovskite materials and the interface charge transfer process of photodetectors at the molecular level,and possesses potential applications for other optoelectronic devices.