| In recent years,metal halide perovskite(ABX3)has attracted wide attention in photovoltaic devices,light-emitting diodes,lasers,photodetectors,scintillators,etc.Although the halide metal perovskite has fascinating characteristics,the presence of lead in the chemical composition is regarded as one of the main limiting factors hindering its commercialization.Using non-toxic/low-toxic elements to skillfully replace the central element lead is the key decision to solve the toxicity and stability problems of these compounds.Therefore,the promising direction of lead-free optoelectronic devices has been derived.The halide double perovskite structure A2B(Ⅰ)B(Ⅲ)X6,which allows flexibility in adjusting the composition of various elements,was produced during extensive exploration.Here,the latest progress and bottlenecks in crystal structure,material preparation(nanocrystalline,microcrystalline,single crystal,thin film),luminescence dynamics,stability and optoelectronic applications of leadfree halide perovskite are mainly introduced.A prospective research strategy to improve the photoelectric properties of the existing materials is proposed,which may help to find the leadfree halide double perovskite with better performance.Compared with three-dimensional perovskites,low-dimensional perovskites exhibit significantly different properties due to strong quantum confinement and octahedral isolation,which requires continuous and comprehensive understanding and exploration.Low-dimensional double-perovskites have very different photophysical properties compared with their single/bimetallic analogues,which has stimulated the in-depth study of this kind of unexplored mixed metal double-perovskites.In particular,the reduction of the size of the inorganic sublattice through the inclusion of organic molecules should be further studied as a strategy to change from indirect bandgap materials to direct bandgap materials.In this paper,a series of two-dimensional(2D)all-inorganic double perovskite nanocrystals,two-dimensional and one-dimensional(1D)organic-inorganic hybrid double perovskite single crystals,microcrystals and thin films were designed and synthesized based on low-dimensional lead-free double perovskite materials,and a reasonable fluorescence mechanism was proposed for the corresponding optical behavior of the materials.Finally,according to their optical characteristics,ultraviolet light detectors and electroluminescent diodes are made.The main work and contents are summarized as follows:(1)Here,we report the first colloidal synthesis of a new type of lead-free halide quadrupleperovskite NCs.The PL quantum yield(PLQY)and charge-carrier lifetime of quadrupleperovskite NCs can be enhanced by 96 and 77-fold,respectively,via metal alloying.Study of charge-carrier dynamics provide solid evidence that the PL enhancement is due to the elimination of ultrafast(1.4 ps)charge-carrier trapping processes in the alloyed NCs.Thanks to the high crystallinity,low trap-state density and long carrier lifetime(193.4 μs),the alloyed quadruple-perovskite NCs can serve as the active material for high-performance photodetectors,which exhibit high responsivity(up to 0.98×104 A/W)and an external quantum efficiency(EQE)of 3×106%.These numbers are among the highest for perovskite-NC based photodetectors.(2)Strong carrier-phonon coupling induced self-trapped excitons(STEs)limit the application of 2D double-perovskites in optoelectronic devices,due to separation and collection of the highly localized STEs are challenging.In this study,we incorporate antimony(Sb)into(BA)4AgBiBr8(BA=CH3(CH2)3NH3+)to form(BA)4AgSbxB1-xBr8(0≤x≤1)trivalent-metal alloyed 2D double-perovskites.We find the carrier-phonon coulping strength decreased greatly in(BA)4AgSbxBi1-xBr8(0≤x≤1)2D double-perovskites with increasing Sb content.The decreased carrier-phonon coupling changes STEs from ’dark’ states to ’bright’ states at room temperature,which opens the possibility to efficiently separate and collect STEs in(BA)4AgSbxBi1-xBr8 2D double-perovskites.We further fabricated photodetectors based on(BA)4AgSbBr8 crystals.The photodetectors exhibit high responsivity up to 1368 A/W,and external quantum efficiency of 4.7×105.These figures are over 3 times higher than that in(BA)4AgBiBr8-based photodetectors.This study provides a unique strategy for developing high performance optoelectronic devices based on STEs.(3)Double perovskites are one of the most promising candidates for developing white light-emitting diodes(WLEDs)owing to their intrinsic broadband emission from self-trapped excitons(STEs).Translation of three-dimensional(3D)Double perovskites to one-dimensional(1D)analogues,which could break the octahedral tolerance factor limit,is so far remaining unexplored.Herein,by employing a fluorinated organic cation,we report a series of highly luminescent 1D double perovskites-inspired materials,(DFPD)2B(I)InBr6(DFPD=4,4difluoropiperidinium,B(I)=K+and Rb+).Highly efficient warm-white photoluminescence quantum yield of 92%is achieved by doping 0.3%Sb3+in(DFPD)2KInBr6.Furthermore,single-component warm-WLEDs fabricated with(DFPD)2KInBr6:Sb yield a luminance of 300 cd/m2,which is one of the best-performing lead-free metal-halides WLEDs reported so far.Our study expands the scope of In-based metal-halides from three-dimensional to one-dimensional,which exhibit superior optical performances and broad application prospects. |
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