Synthesis Of Multi-Doped Pure-Red CsPb（I/Br/Cl）₃:Ga Perovskite Quantum Dots And Their Application In Light-Emitting Diodes

All-inorganic perovskite CsPbX₃（X=Cl,Br,I）quantum dots（QDs）and their light-emitting diodes （PeLEDs）have shown great potential for application in next-generation display and lighting technology,due to their excellent luminescent characters,such as easily tunable wavelength,narrow spectral line width,high-temperature tolerance,simple solution processing,low cost,etc.Compared with the rapid development of green and blue PeLEDs,the research on pure-red PeLEDs has seriously been lagged.Therein,the pure-red perovskite QDs in mix-halide system such as CsPb（I/Br）₃QDs readily experience phase separation due to ion migration under voltage bias,and cannot maintain the color stability,which limits the development of pure-red PeLEDs.To address this problem,we attempt to emphasize the role of Cl^-doping in obtaining pure-red perovskite QDs in the mixed halide system,namely Cl^-doped CsPbI₃ and CsPb（I/Br）₃ perovskite QDs.In addition,according to the"soft and hard acid-base theory",Cl^-has a high electronegativity and low polarizability,which is a hard base.In this thesis,specific hard acid cations are introduced along with hard base Cl^-precursors in order to enhance the hard acid-hard base interactions.When the hard acid cation is doped into the perovskite lattice,it may synergistically promote the doping of hard base Cl^-,i.e.,synergistic doping effect.Based on this concept,small-sized hard acid cation,typically such as Ga³⁺with high positive charge density,is selected in this thesis.Ga³⁺and Cl^-can be introduced simultaneously by a single precursor GaCl₃,which is expected to synergistically dope into the CsPbI₃ or CsPb（I/Br）₃ lattice.The doping of small-sized Ga³⁺and Cl^-may lead to the compression of the perovskite lattice and the change of its energy band.Hard acids and bases have strong interaction forces,and the hard acid Ga³⁺in the doped perovskite lattice is expected to"anchor"the hard base Cl^-/Br^—,which helps to suppress the phase separation phenomenon of mixed halogen perovskites and prepare high-quality CsPb（I/Cl）₃.In this thesis,we focus on the influence of Ga³⁺and Cl^-co-doping on the crystal structure and luminescence properties of perovskite QDs by controlling the thermodynamic parameters,such as synthesis temperature and dopant concentration,during the synthesis of perovskite QDs.Furthermore,we have fabricated the PeLEDs based on the obtained pure-red perovskite QDs.For device optimization,different hole and electron transport layer materials are selected from the perspective of carrier mobility,energy level matching and interfacial exciton quenching,etc.,and attempts are made to construct a gradient transport layer structure,optimize the thickness of each film layer,balance carrier injection,and prepare efficient and stable pure-red PeLED devices.Following is the main work as carried out:Ⅰ.We explored the synthesis methodology of GaCl₃-doped CsPbI₃ QDs（CsPbI₃:GaCl₃）.The pristine CsPbI₃ QDs and GaCl₃-doped CsPbI₃:GaCl₃QDs were synthesized by the typical hot-injection method.We further optimized the synthetic parameters for achieving high-quality perovskite QDs,such as reaction temperature,surface ligands,precursor ratio and dopant concentration.In addition,the crystal structures and optical properties of the obtained perovskite QDs were studied in detail.Ⅱ.We further explored the synthesis of CsPb（I/Br/Cl）₃:GaQDs.We investigated the effects of different anion and cation doping ratios on adjusting the luminescence wavelength of pure-red perovskite QDs,stabilizing the perovskite crystal structure,and eliminating the internal defects of the crystal.And on this basis,the synthesized CsPb（I/Br/Cl）₃:GaQDs were subjected to short-chain ligand exchange,together with halide anion exchange for bright pure-red QDs.Ⅲ.Based on the synthesized CsPb（I/Br/Cl）₃:GaQDs,we further fabricated the pure-red PeLEDs.We optimized the device architecture with different functional transport layer materials from the viewpoints of carrier mobility,energy level matching and interfacial exciton quenching.We further constructed gradient transport layer structure and optimized the thickness of each functional thin film layer to promote the charge injection balance,thereby enhancing the PeLEDs performance.As a result,the PeLEDs based on CsPb（I/Br/Cl）₃:GaQDs exhibited pure-red color with spectral stability under voltage bias,indicating suppressed phase separation phenomenon in our system.