| Novel halide perovskite materials have attracted much attention due to their excellent photoelectric properties.The photoelectric conversion efficiency of thin film solar cells based on these materials has exceeded 24.2%in just ten years.In addition,they have also shown great application prospects in laser,light emitting diode,detector and so on.Compared with polycrystalline thin films,perovskite single crystal thin films have no holes,grain boundary and lower charge defect density,so they have higher carrier mobility,longer carrier diffusion length and carrier lifetime,and have great potential for the preparation of photoelectric devices with higher performance.To ensure the efficient transmission and collection of carriers,the growth of single crystal thin films with thickness less than carrier difEusion length becomes the precondition for the fabrication of high performance photodetectors and solar cells.However,it is very difficult to obtain perovskite single crystal thin films by traditional thin film preparation methods.Despite the fact that many research groups around the world have carried out relevant work and made considerable progress,it is still a great challenge to obtain high quality,namo-thick and large-area single crystal films of perovskite materials.In this paper,perovskite single crystal films were prepared from three aspects:three-dimensional organic-inorganic composite perovskite materials,two-dimensional organic-inorganic composite perovskite materials and all-inorganic perovskite materials.The crystalline quality,crystal structure,photophysical properties and photoelectric properties of the obtained single crystal films were characterized in detail,and their application prospects were predicted.The acquisition of these novel single crystal films is of great significance to the device performance improvement of perovskite materials in the field of optoelectronics and so on.This paper is divided into six chapters.The main contents of each chapter are as follows,In the first chapter,the research background of new perovskite single crystal thin films is introduced.The novel perovskite materials,the basic knowledge of thin films,the growth methods of perovskite polycrystals and single crystal thin films as well as their applications in vaious fields are summarized.Based on the above summary,we put forward the basis,design ideas and research contents of this paper,and briefly summarized the main contents of each chapter.In the second chapter,the experimental reagents and devices used in the growth of new perovskite single crystal films are introduced,and some basic performance testing methods and instruments are described in detail.In the third chapter,based on the simple structure and excellent properties of CH3NH3PbBr3,the growth habit of the material was studied.According to the growth behavior of the crystal in organic solvents,we proposed for the first time to fabricate the single crystal film of the material by physically space-constrained clamping method.By improving the growth device and conditions,single crystal films with a maximum area of more than 3×4 mm2 and thickness range from 500 nm to 5 μm can be obtained,and can be fabricated on various substrates,such as glass,conductive glass,silicon wafer and so on.The quality of the obtained single crystal films was characterized,and their basic optical physics and ultrasonic properties were studied,which laid an experimental foundation for exploring the accurate carrier transmission distance and other issues.For the first time,a gas-phase post-processing method was designed to transform CH3NH3PbBr3 into CH3NH3PbI3 that is difficult to be prepared into single crystal thin films directly.The optical response performance of the CH3NH3PbI3 film was preliminarily investigated.The on-off ratio was twice as high as that before the conversion.In the fourth chapter,based on the two-dimensional structure characteristics of(C3H7NH3)2PbBr4 and(C6H13NH3)2Pbl4,we improved the original solution cooling rowth method devices to grow them.For the first time,thin single crystals with an area of nearly 1 cm2 and a thickness of 150 μm were grown by acid solution.The thermal properties were characterized and the two phase transitions at 278 K and 171 K were studied by single crystal analysis for the first time.The optical properties of(C3H7NH3)2PbBr4 single crystal thin films were characterized comprehensively.The up-conversion and two-photon properties of(C3H7NH3)2PbBr4 were found for the first time,and the optical waveguide properties were tested.The optical loss was 12.2 dB/cm.It is the first time to predict the application of this material in the field of frequency-band converted optical waveguide communication.In the fifth chapter,considering the poor thermal stability of organic-inorganic composites,we have explored the all-inorganic Cs-Pb-Br compounds that have good thermal stability.For the first time,other phases except cubic phase have been resolved at room temperature.Because adjoint crystallization is very easy to occur in the growth of this kind of material,fractional crystallization technology was introduced for the first time to grow CsPb2Br5 single crystal thin films.How to prevent the adjoint crystallization and deterioration was studied in detail.The crystallization,growth process and growth phenomena were observed in detail.The obtained high quality single crystal thin films were used to characterize their optical and thermal properties.Its fluorescence excitation peak is at about 250 nm,which has great application prospects in the field of deep ultraviolet detection.It has excellent cyclic thermal stability in the range of 0～200 ℃,which lays a foundation for its application in device stability.Electrical properties tests show that the conductivity of the films varies greatly within and between layers,which indicates their important application prospects in the field of directional switches.In the sixth chapter,we summarize the main contents and conclusions of this paper,innovations and work to be further carried out. |
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