Copper-lodide Hybrid Cluster-Based Highly Luminescent Materials: Design, Synthesis And Device Application

Copper-iodine(Cu-I)hybrid clusters are a type of organic-inorganic hybrid materials composed of copper-iodine inorganic units and organic ligands.They have high luminescent efficiencies,adjustable optical band gaps,diverse structures,simple preparation methods,and easy scale-up routes,so that they have received extensive attention in the field of optoelectronics.At the same time,copper halides are abundant in earth,low in price environmental toxicity,making them expected to become effective substitutes for noble metals and rare earth elements.Thus,exploring new Cu-I hybrid cluster-based luminescent materials pocesses high practical application value and great industrial production potential.However,due to the structural rigidity of the cluster itself and the instability of the coordination bonds,the dispersion and stability of such clusters in solvents have certain limitations,and most types can only be processed in the form of powder.As the processability of materials plays an essential role in the integration of application devices,so their related application research is only in its infancy comparing with other metal complexes.The application of this type of material is still mostly converged in the aspect of solid-state lighting,including phosphor powder and a small amount of organic light-emitting diode devices.However,considering its overall performance,we believe that Cu-I hybrid cluster-based luminescent materials have great application space and development prospects.Therefore,based on the research of Cu-I hybrid cluster materials,with the intention of enlarge the application range of this type of cluster,we work on solving the problems of poor solubility,poor dispersion and poor stability while ensuring excellent luminous performance by designing new synthetic strategies and novel cluster structures,together with enhancing the solution processing properties of them.Combined with structural optics,we realize the special optical properties of this type of clusters at the same time.Finally,we obtained a series of highly efficient luminescent Cu-I hybrid cluster materials with multifunctional application properties.The main accomplishments of our project are as follows:1.By developing the strategy of introducing long-chain polymer polyvinylpyrrolidone(PVP),we improved the solvent dispersibility of Cu-I hybrid clusters.We selected all-in-one structured Cu4I6(pr-ted)2 hybrid clusters as the basic high-efficiency light-emitting unit.The anionic Cu-I inorganic unit was effectively dispersed with the help of PVP micelles.Followed by the addition of pr-ted cationic ligand,we finally obtained highly dispersed Cu4I6(pr-ted)2 nanoparticles.The method is simple and easy to operate,so large-scale preparation of these nanoparticles can be realized.The obtained Cu4I6(pr-ted)2/PVP composite nanoparticles can be well dispersed in ethanol to form environmental-friendly luminescent ink,and its photoluminescence quantum yield(PLQY)can reach over 90%,together with a wide Stokes shift of 113.8 nm,suggesting their effective energy conversion ability from ultraviolet light to green light.The image drawn by the luminescent ink shows good anti-counterfeiting effect.In addition,by mixing it with the polymer matrix in proportion,the preparation of a large-area luminescent film can be realized.The obtained film has unique advantages of high luminescent efficiency,high light transmittance and low reabsorption loss,which enable them great application potential in the coatings of solar cell concentrators.2.By introducing symmetrical bidentate ligands to effectively connect copperiodine inorganic units,we construct novel Cu-I hybrid clusters with a one-dimensional ordered structure and realize their PL emission with special optical properties.We sythesized a series of Cu2I2-dimer hybrid crystals by precise growth by slow diffusion method,and these crystals all exhibit highly oriented Cu2I2 inorganic unit structures,among which the quasi-two-dimensional(2D)Cu2I2-4,4’-bpy hybrid crystal realized linear polarized PL emission with a degree of as high as-0.96.Using the first-principles calculation,we manifest that the high-efficiency linearly polarized emission of the hybrid crystal is mainly derived from the highly consistent alignment of the transition dipole moments in the hybrid crystals.Furthermore,we developed a microemulsion methode for Cu2I2-dimer-based hybrid nanocrystals that can be effectively dispersed in deionized water,among which Cu2I2-4,4’-bpy nanobelts achieved both high PLQY(64%)and ultrahigh polarization degree(～0.99).As a special light source with strong polarization properties,it can provide the possibility of application in important optical fields inclusive of three-dimensional(3D)display and specific biological imaging.3.By introducing chiral bisphosphine ligands to asymmetrically modify Cu-I inorganic units,we construct novel clusters with chiral optical emission properties while improving their stability and solubility to achieve solution processing and cluster assemble.We introduced the axially chiral R/S-BINAP ligand into the Cu-I system and prepared novel R/S-Cu2I2(BINAP)2 binuclear clusters.Benefiting from the biphosphine chelation of the ligand,the stability of the obtained chiral clusters were greatly improved,and it can be stably dissolved in polar solvents such as dimethyl sulfoxide(DMSO).We realized the asymmetric aggregation assembly of this chiral cluster by solution processing and thus obtained chiral crystal materials with high-efficiency circularly polarized luminescence(CPL),including hexagonal platelet microcrystals(glum～9.5×10-3)and highly oriented crystalline films(glum～5×10-3).Finally,we prepared an electroluminescence device using the chiral thin film as the light-emitting layer.The EL brightness of the obtained device can reach to about 1200 cd m-2,manifesting the broad application prospects of Cu-Ⅰ hybrid clusters in the construction of special light sources and functional electroluminescent devices.4.By simultaneously introducing bridging N-containing ligands and solubilizing P ligands,we construct novel clusters with both high luminescent efficiency and ultrahigh solubility.The CuI-Pyrphos cluster obtained by our double-ligand modification strategy has a solubility of more than 200 mg/mL in N,N-dimethylformamide(DMF)solvent,and we have demonstrated its structure conservation in DMF solvent environment through a series of characterizations.The film processed by DMF solvent has both low surface roughness(～0.22nm)and high PLQY(～70%),which is wellincorporated in solution-processed light-emitting diode(LED)devices through a crosssolvent strategy.Without the doping of any host material,the LED device has highefficiency warm white light emission,with a maximum EQE of 19.1%,a high brightness exceeding 40000 cd m-2,and the working life reaches 140 hours(T50@100 cd m-2).Meanwhile,our large-area(36 cm2)LED devices fabricated by blade-coating process also exhibit uniform and bright warm-white emission.In addition,by modifying the bridging ligands,a series of solution-process LED devices with tunable colors have been prepared,demonstrating the practical application potential of Cu-Ⅰhybrid cluster materials in the field of electroluminescence such as LED panel display and low-cost solid-state lighting.