Study On The Growth And Properties Of New Hybrid Halide Perovskite Single Crystal Materials

Hybrid perovskite materials with distinctive semiconductor properties have attracted more and more interests in the optoelectroninc fileds,including solar cell,ferroelectricity,thermoelectricity,field-effect transistors?FETs?,photodectectors and light emitting diodes?LEDs?,etc.However,most of the reports are based on the polycrystalline hybrid perovskite thin film materials.Many physical properties remain to be solved regarding to the carrier mobility,ferroelectricity,mechanism for photoelectric conversion,toxicity of Lead?Pb?,stability of these materials and so on.Single crystals are the best candidates for studying the intrinsic properties of these materials.And thus,it is imperative to carry out the research on these crystal materials.Based on these reasons,our research group have grown a series of bulk hybrid halide perovskite single crystals by solution methods for the first time.The fundamental properties,such as thermal,optical,electric properties,phase transition and stability of these materials,were characterized and the related thin film solar cells were preliminarily explored.Their crystal growth and properties research would pave way for understanding intrinsic properties and extending further applications of these hybrid perovskite materials.The dissertation contains seven chapters,the main contents of each chapter in as follows,In the first chapter,we introduced the research background of hybrid perovskite materials,concentrated on the crystal strucuture,crystal growth methods and their applications of these hybrid perovskite materials.Based on these backgrounds the design ideas and reaserach contents of this dissertation were presented,and the main contents of each chapter were summarized.In the second chapter,we described the reagents used in the experiments,bulk crystal growth apparatus and growth condition parameters for these hybrid perovskite single crystals.And the measurements and instruments for some intrinsic properties of hybrid perovskite materials were elaborated in detail.In the third chapter,we reported the syntheses,bulk growths,crystal structures and fundamental properties of CH₃NH₃PbX3?X=Br,I?single crystals.Especially,the bulk growth of CH₃NH₃PbI₃ single crystal was investigated for the first time.The explorations and optimization of the single crystal growth condition were undertaken further.Moreover,the structural phase transition of CH₃NH₃PbI₃ single crystal by dielectric properties,specific heat and variable temperature-dependent single-crystal X-ray diffraction measurements.The phase transition points of CH₃NH₃PbI₃ single crystal existed at 331 K and 175 K.There existed the obvious anisotropy of thermal expansion and thermal conductivity in CH₃NH₃PbI₃ single crystal,and the above phase transition processes were all reversible.Meanwhile,there existed obviously anisotropic ferroelectric domain structures observed by piezoelectric response microscope?PFM?measurements.In the fourth chapter,based on the characteristics of bulk growth habit,poor machining performance and difficulty in single-crytalline device fabrications,our research group introduced the long-chain butylamine cation or thiocyanate anions into CH₃NH₃PbI₃ material.The layered hybrid perovskite?n-C4H9NH3?2?CH₃NH₃?n-1PbnI₃n+1?n=1,3,4?single crystals by temperature-lowering method and MA2Pb?SCN?2I2 single crystal by slow-evaporation method were investigated by our research group.Their crystal structures and fundamental properties were also characterized.Especially,the crystal structure of MA2Pb?SCN?2I2 belonged to non-centrosymmetric orthorhombic space group Pmn21 and there existed obvious endo/enxo peaks ranging from 335 K to 340 K by single-crystal X-ray diffraction,DSC and TGA measurements,demonstrating possible ferroelectric phase transition.Meanwhile,the tunable band gaps and obviously different photo-response of C4H9NH3)2?CH₃NH₃?n-1PbnI₃n+1?n=1,3,4?single crystals were investigated by UV-vis-NIR spectra and photo-response measurments.The maxium photo-response value?ION/OFF?under white light illuminations was up to 562.These layered perovskite materials were all excellent semiconductors.In the fifth chapter,considering the toxicity of lead?Pb?element,our research group substituted tin element for lead element in CH₃NH₃PbI₃ and CH?NH2?2PbI₃.Bulk single crystals of ASnI₃?A= CH₃NH₃,CH?NH2?2?were obtained by top-seeded solution growth?TSSG?method.And their crystal structures and intrinsic properties were measured.These results demonstrated that the stability of CH?NH2?2SnI₃ single crystal is better than CH₃NH₃SnI₃ single crystal when exposed to ambient atmosphere.With this reason,the premimilary exploration of CH?NH2?2SnI₃ thin film solar cell were performed to obtain the PCEs of about 1.0%.Besides,considering the poor stability of CH₃NH₃SnI₃ single crystal in the ambient atmosphere,lead element in CH₃NH₃PbI₃ was partly replaced with tin element to obtain mixed Sn/Pb hybrid perovskite CH₃NH₃Sn0.62Pbo.3sI₃ single crystals.These single crystals were still stable when exposed to ambient atmosphere for three months.In the sixth chapter,based on the debate in the phase transition and crystal structure problems of NH?CH₃?₃ SnX3?X=Cl,Br?,our research group have obtained bulk NH?CH₃?₃SnX3?X=Cl,Br?single crystals by bottom-seeded solution growth?BSSG?method.Their fundamental properties including crystal structure,phase transition and stability were systematically investigated.NH?CH₃?₃SnX3?X=Cl,Br?single crystals both exhibited the acentric crystal sturctures by DSC,variable temperature-dependent second harmonic generation?SHG?and variable temperature-dependent single crystal X-ray diffractions.The results of powder SHG at 1064 nm laser radiation indicated that they were not type-I phase matchable.NH?CH₃?₃SnCl3 single crystal existed only one phase transition point?277 K?,at which the reversible structural phase transition was from orthorhombic space group Cmc21 to monoclinic space group Cc.Moreover,NH?CH₃?₃SnBr3 single crystal belonged to orthorhombic space group Pna21.These results clarified the phase transiton and crystal structures problems of these hybrid perovskite materials.The last chapter summarized the main contents and conclusions,creative work and further work to be done in this dissertation.