Crystal Design,Growth And Energy Transfer Of Halide Perovskites

Lead halide perovskites have undergone a surge in popularity for perovskite solar cells,lasers,light-emitting diodes and high-energy detectors,due to their superior photovoltaic properties（e.g.,low exciton binding energy and long carrier diffusion length）and photoluminescent performance（e.g.,wide color gamut and high photoluminescence quantum yields（PLQY））.However,they suffer from lead toxicity and long-term instability,which arouse great interest of lead-free perovskite exploration.Novel lead-free halide perovskites could be designed by heterovalent and homovalent substitution for Pb site compositional engineering,such as double halide perovskites and quadruple halide perovskites and their derivatives.In this work,the outcome of experimental results（i.e.,crystal structure analysis and spectroscopic analysis）combined with theory calculations（i.e.,first-principles calculations on thermodynamic properties and electronic properties）clarify the relationship between crystal structure properties and energy transfer of halide perovskites,providing meaningful guidance for their application exploration.The main contents and innovations of this paper included as fellow:（1）Novel quadruple halide perovskites with remarkable optical properties were designed by compositional engineering.The experimental results,in conjunction with theory calculations,reveal crucial insights into the energy transfer characteristics within the bandgap.In this work,we propose a strategy for designing quadruple perovskites by heterovalent cation transmutation from double perovskites.Two stable quadruple perovskite halides,i.e.,Cs₄Cd Sb₂Cl₁₂ and Cs₄Cd Bi₂Cl₁₂,with a vacancy-ordered three-dimensional（3D）crystal structure were predicted through symmetry analysis and density functional theory（DFT）calculations.The title perovskite halides are also electronically 3D with direct forbidden bandgaps.Following the indication provided by DFT results,Cs₄Cd Sb₂Cl₁₂ and Cs₄Cd Bi₂Cl₁₂ as unique quadruple perovskites were successfully synthesized by a solvothermal method.The steady-state photoluminescence（PL）shows the wide emission,while the transient PL exhibits carrier recombination lifetime on the order of microseconds at low temperature.The quadruple perovskite halides provide an alternative platform for promising optoelectronic materials design in addition to simple and double perovskites.（2）The outcome of experiments combined with DFT calculations are used to select out double and quadruple bromide perovskites,which enable the charge transfer between metal cations and bromide anions within their structures.This charge transfer can be a reliable driving force to reversible solidify and release bromine.We propose a Br₂-free solvothermal method to prepare vacancy-ordered bromide perovskites(e.g.,Cs₄Sb₂Br₁₂and Cs₂Pd Br₆)for the bromine fixation.Heating and cooling the title bromide perovskites in a necked ampoule make the bromine visible and separable from the solid residue.Solvent extraction（e.g.,water and ethanol）can also release bromine from the bromide perovskites.The composition engineering(i.e.,Cs₄Sb₂Br₁₂ vs Rb₄Sb₂Br₁₂,and Cs₄Sb₂Br₁₂ vs Cs₂Pd Br₆)can effectively tune the stability（against water and high temperature）and the bromine storage capacity（from 9.30%to 18.76%）.In addition,this work can provide a one-step preparation method for the liquid bromine without further purification.（3）The outcome of experiments and DFT calculations are utilized to select out double and quadruple chloride perovskites,which enable the charge transfer between metal cations and chloridion within their structures.This charge transfer can be a reliable driving force to reversible capture and release chlorine.Herein,several vacancy-ordered chloride perovskites(i.e.,Cs₂Pb Cl₆,Rb₂Pb Cl₆,（NH₄）₂Pb Cl₆,and Cs₄Sb₂Cl₁₂)for elemental chlorine solidification were firstly synthesized by a Cl₂-free solvothermal method.The experimental and theoretical results indicate that the release–storage of Cl₂gas depends on the reversible redox between metal cations and chloridion.Both thermal heating and solvent soaking could trigger the release of Cl₂ in perovskites.The stability and Cl₂ storage performance（from 5.9 wt%to 16 wt%）of vacancy-ordered chloride perovskites can be tuned by composition engineering.Compared with the porous adsorption materials,Cs₂Pb Cl₆ has the highest reversible storage capacity of Cl₂.（4）Cd/Mn halide tetranuclear are assembled with piperazidine cations resulting in a series of perovskite-like supramolecular structures.The energy transfer properties within the bandgap are investigated by crystal structure and spectroscopic analysis.The title crystals include non-emission(C₄H₁₂N₂)₃（NH₄）₄Cd₄Cl₁₈（namely,1）,pink emission(C₄H₁₂N₂)₃（NH₄）₄Mn₄Cl₁₈（namely,2）,red emissions(C₄H₁₂N₂)₃（NH₄）₄Mn_0.81Cd_3.19Cl₁₈（namely,Mn-1,PLQY of 92.6%）and yellow emission(C₄H₁₂N₂)₃（NH₄）₄Sb_0.02Cd_3.98Cl₁₈（namely,Sb-1,PLQY of 89.4%）.Dopant ions can lower the crystalline symmetry and hybridize different atomic orbitals to break the forbidden transition resulting in enhanced luminescence property.The structure–property relationship is studied through the composition engineering.The experimental results indicate that the emission of 2 and Mn-1 originates from ⁴T₁（⁴G）→⁶A₁（⁶S）transition of Mn（II）,while ³P₁→¹S₀ transition of Sb（III）in clusters directly contributes to the emission of Sb-1.Based on outstanding photoluminescence performance,Mn-1 and Sb-1 have been fabricated into white light-emitting diodes（WLEDs）devices.Significantly,the super-high luminous efficacy of 439 lm/W（exceeding the market standard in 2022 setted by The United States Department of Energy（250 lm/W））,a high color rendering index（CRI）of 81.7 and a low correlated colour temperature（CCT）of 4536 K can be achieved by combining Mn-1 and commercial（Ba,Sr）₂Si O₄:Eu²⁺phosphors on the 430 nm In Ga N chip.In addition,the water-soluble Mn-1 shows potential applications in X-ray scintillator,luminescent ceramic,flexible film and luminescent imaging agents.In summary,the discovery of tetranuclear metal halide clusters establishes a new strategy for constructing promising emissive materials.