Crystal Structure And Charge Transport Properties Of The Lead Halide Peroveskites Engineered By Naphthalene Diimide Ammonium

Hybrid organic-inorganic lead halides have attracted immense attention of late in photovoltaic devices,lightemitting diodes,field-effecttransistors(FETs)and phototransistors,and nonlinearopticsfor their remarkable optoelectronic properties and ease ofpreparation,which have opened up new opportunities for nanoelectronics and optoelectronics.The halideperovskites exhibit great chemical flexibility,leading to rich andvaried structure and function.Methylammonium lead iodide(CH3NH3PbI3)was the most extensively studied compound,which have strong optical absorption,high charge-carrier mobilities,and exciton-diffusion lengths on the order of microns.However,the three dimensional(3D)CH3NH3PbI3 is unstable toward the moisture,which severely limits it application.Changing the size and structure of the organic cation to reduce the dimension of perovskite can improve the stability effectively;meanwhile adjust the quantum well effect to regulate its photoelectric properties.From a standpoint of functionalmaterial design,an attractive approach is to incorporate?-conjugated chromophoremolecules,which is expected to further optimize the absorption and charge transport properties of the materials through the organic-inorganic synergistic effect.Accommodation of organic molecules with distinctive structures into hybrid perovskites is significantly underestimated,and the influence of the ?-conjugate molecules on the structure and charge transfer of perovskite is almost uninformed.In this paper,using theammonium-linkednaphthalene diimide(NDIAs)as the organic cation,two single crystals of(NDIA)4Pb3I10 and(NDIA)2Pb2Br6were synthesized respectively.The intrinsic charge-carrier transport properties of the crystals were evaluated by field-effect transistors(FETs)measurements,and the relationship between the structure and charge transport was explored,so as to guide the design ofnovelty hybrid perovskites.The main contents of this thesis are as follows:1.Synthesis and ambipolar transport properties of the 2D(NDIA)4Pb3I10single crystal(NDIA)4Pb3I10 crystals with the shape of oblique hexagonal plates were obtained solvothermally with starting materials of NDIA-I?PbI2,and HI solution.Solid(NDIA)4Pb3I10 crystallizes in the acentric monoclinic space group P21/n.The whole structure is formed by alternating layers of Pb-I sheets and NDIA cations,which stacks along the b-axis.Structure determination reveals an extraordinary<110>-oriented lead iodide sheets separated by NDIA bilayers.The presence of NDIA promoted the lead iodide octahedron to form the unique three-point coplanar[Pb3I10]4-unit,which then connected into 2D network in a corner-sharing manner.The NDIA cations closely stacked into 1D chains within the bilayers that being sandwiched between the inorganic layers.FET characteristics of the single crystal obtained at room temperature demonstrate balanced electron and hole transport with mobilities reach up to more than 5×10-3 cm2 V-1 s-1 without evident hysteresis.The crystal maintained in solvent keep stable without decompose,and the FET devices demonstrated good charge transfer performance without attenuation after stored in air for one week.The 1D stack of NDIAs contributes greatly to the performance improvement for both the charge transport and the stability.2.Effect of halides on the structure and charge transport of the organic-inorganic hybrid perovskites(NDIA)2Pb2Br6 crystals were obtained solvothermally with starting materials of NDIA-I?PbI2,and HBr solution.(NDIA)2Pb2Br6is crystalized in the shape of oblique hexagonal plates.The crystallographic data show that the single crystal is composed of Pb-Br one-dimensional structure,and the single crystal structure is monoclinic P1/2 space group.Pb-Br octahedron is arranged along a-axis in a co-vertex manner to form a one-dimensional chain structure.Templated by the Pb-Br chain,the cations of Pb-Br arranged in one dimensional order at the top and bottom of the chain respectively by hydrogen bonding,which resulted in the formation of organic-inorganic-organic sandwich layered structure.The lamellar stacking along the c-axis is formed by the hydrophobic interaction between the NDIA side chains.The properties of FET devices were measured by using the single crystal structure as charge transfer layer.The FET curve shows excellent p-?n-bipolarity.The mobility is as high as 6 cm2V-1S-1,the hysteresis is not obvious,and the stability is good.On account of the different electronegativity and ionic radius between iodine and bromine,two crystals with distinct structure in one and two dimensions of lead halide are obtained,and the mechanism of charge transfer is studied for the first time by FET measurements.Considering the contact resistance and thickness of the crystals,the mobility can further be improved in the future work.The research in this paper provides important clues for construction of functional perovskite structures,as well as regulation and understanding of charge transport restrictions.