Study On The Growth And Properties Of Lead-free Low-dimensional Organic Metal Halide Single Crystals

Benefiting from the superior photophysical properties,organic metal halide materials have risen rapidly in the field of optoelectronics as one of the most popular solution-processable materials.Especially,remarkable progress has been made in the photovoltaic applications.Thanks to their unique chemical and structural diversity,the reasonable combination of different organic components and metal halides inorganic components can adjust the connection mode of the metal halide polyhedra,so as to achieve organic metal halide materials with different dimensions from three-dimensional(3D),two-dimensional(2D),one-dimensional(1D)to zero-dimensional(0D)at the molecular level,which provides a material platform for exploring the diversity of tunable structure,energy band and photoluminescence properties.Among them,the rich chemical components and crystal structure types of the low-dimensional organic metal halide materials endow them with unique properties,such as broadband emissions with large Stokes shift,anisotropic carrier transport and mechanical flexibility,enabling them great potential in the fields of lighting,display and flexible optoelectronic applications.Up to now,there are still some problems in the development of low-dimensional organic metal halide materials.For example:(1)Lead-based organic metal halide materials are still the mainstream in the research,and toxic lead will hinder their practical commercialization.Therefore,it is of great significance to promote the development of lead-free organic metal halide materials with excellent photophysical properties;(2)It is still challenging to improve the stability and performances of low-dimensional organic metal halide luminescent materials,and it is of great guiding significance for designing new high-quality luminescent materials by further understanding of the relationship between their properties and chemical composition/structure;(3)At present,most organic metal halide based-optoelectronic devices are made of polycrystalline films,and the defects at grain boundaries will deteriorate the device performances and stability.However,the growth and preparation of single-crystalline films still face difficulties.In order to realize efficient optoelectronic devices,it is needed for further exploration and research on the growth of high-quality crystalline-films;(4)It is found to be of certain difficulties to integrate low-dimensional organic metal halide materials to flexible electronic devices,it is urgent to explore organic metal halide flexible materials with excellent photoelectric properties.Based on the above problems,series of novel lead-free low-dimensional(0D-1D-2D)organic metal halide single crystals were designed and grown by simple solvent evaporation method and solution cooling method.The detailed researches are carried out relating to the crystal structure,thermal,photophysical,electrical and other intrinsic properties.The relationship is revealed between the crystal structure and intrinsic properties.Moreover,the flexible optoelectronic devices are fabricated,and the device performances are studied systematically.The main research contents are as follows:(1)By introducing large-sized[C5H14N2]2+organic molecules,novel Mn2+ based-0D organic metal halide(C5H14N2Br)2MnBr4 luminescent crystals have been designed and grown by simple solvent evaporation method.The(C5H14N2Br)2MnBr4 crystallizes in the typical 0D structure,including isolated[MnBr4]surrounded by[C5H14N2]2+organic cations and free Br-ions.The shortest Mn-Mn distance is as long as 8.2720 A.Through systematical analyses of the photophysical properties,it is found that the(C5H14N2Br)2MnBr4 single crystal exhibits strong narrow-band green emission with the center at 520 nm(FWHM?43 nm,PLQY?60.7%)at room temperature,originating from the spin-forbidden transition(4T1(G)to 6A1)of tetrahedrally coordinated Mn2+ions.The low cost synthesis method,excellent luminescent properties and good stability demonstrate the potential of(C5H14N2Br)2MnBr4 as narrow-band green phosphors in lighting applications.(2)Novel 0D(C4H9NH3)2MnI4 organic metal halide single crystals are grown,and for the first time the sensitive thermoresponsive-dual-emission phenomenon is observed in the field of organic metal halide materials without doping extra luminescent activators.In the crystal structure of(C4H9NH3)2MnI4,isolated[MnI4]2-tetrahedra were surrounded by[C4H9NH3]+organic cations,forming 0D structure.It exhibits bright red photoluminescence at room temperature.Systematical researches reveal that(C4H9NH3)2MnI4 exhibits two emissions(a narrow-band one with center at 550 nm and a broadband one with center at 672 nm),which are assigned to the d-d transition within Mn2+-centered tetrahedra and self-trapped excitons(STEs)emissions,respectively.Moreover,the relative intensity of the two emission peaks(I672 nm/1550 nm)of(C4H9NH3)2MnI4 shows a linear relationship with temperature,resulting in perceptible transition of the emission color from red to yellow that can be observed during heating,and its PLQY is 68.3%at 70?,making this new class of intrinsic dual emitters attractive for ratiometric optical thermometry.Meanwhile,the disclosed interaction mechanism of photoluminescence decay will be helpful for further exploration of the organic metal halide materials for optical thermometry technologies.(3)A series of novel Sn2+based-low-dimensional organic metal halide single crystals with the different dimensionality are designed and grown by solution cooling method,including 1D(C5H14N2Br)2SnBr4·3H2O and 0D(C5H14N2)2SnI6·3H2O.The single crystal analyses reveal that the 1D(C5H44N2Br)2SnBr4·3H2O comprises of 1D corrugated chain(made up of corner-shared[SnBr6]octahedra)and 0D(C5H14N2)2SnI6·3H2O comprises of isolated[SnI6]octahedra.Both of them emit bright photoluminescence excited by 365 nm UV light at room temperature.By systematical studies of their photophysical properties,both photoluminescence were investigated to be originated from STEs,which are commonly observed in low-dimensional organic metal halide materials.Notably,the PLQY of 1D(C5H14N2Br)2SnBr4·3H2O is as high as 75.8%,to our knowledge,which is among the highest for 1D organic metal halide broadband emitters.This intense PL emission is attributed to the highly distorted[SnBr6]induced-efficient STEs emission.Additionally,1D(C5H14N2Br)2SnBr4·3H2O exhibits excellent thermal stability and luminescent properties,for instance,the thermal decomposition temperature is as high as 600K and PL emission can be observed even at 513K.The low-cost eco-friendly raw materials,simple synthesis method,excellent luminescent properties and stability make this new low-dimensional organic metal halide potential for applications in the fields of lighting-related applications.(4)Based on modified solvent evaporation method,the centimeter-sized Cu2+based-2D organic metal halide(C4H9NH3)2CuBr4 crystalline-films with high quality have been grown successfully.The detail parameters of(C4H9NH3)2CuBr4 single crystal structure have been obtained for the first time.Through detail analyses of its photoelectric properties,the(C4H9NH3)2CuBr4 shows optimal energy gap,long carrier lifetimes,large carrier mobilities as well as good mechanical flexibility.Furthermore,the flexible photoconductive detectors are fabricated based on(C4H9NH3)2CuBr4 crystalline-films,and the devices achieve excellent photoelectric conversion properties,including low dark current(?10-11A),high detectivity(?1011 Jones),good flexibility and stability.This work provides a new way to realize non-toxic,low-cost and high-performance flexible photodetectors with simple device structure.