Preparation And Optical Properties Of Perovskite Quantum Dots Doped By Metal Ions

Perovskite materials have become the key materials for efficient photovoltaic cells,light-emitting diodes,photodetectors and lasers due to their excellent optical properties.At present,the most widely used lead-based perovskite material APb X₃(A=CH₃NH₃⁺and CH₃(NH₂)²⁺)had the highest Power Conversion Efficiency(PCE),which had reached 23.7%.However,due to the general instability of organic perovskite,people began to try to use inorganic CsPb X₃(x=Cl,Br,I)material as a substitute.The results showed that all inorganic Cs based compounds have better composition stability in various environments.Cs based inorganic perovskite quantum dots have attracted much attention due to its advantages of high Photoluminescence Quantum Yield(PLQY),narrow emission spectrum,high absorption coefficient,high carrier mobility,low carrier recombination rate and adjustable emission spectrum in the visible region.But there were still some problems,such as the toxicity of Pb and the stability of I-based perovskite.The main contents of this paper are as follows:Ion doping had become an important method to modify the properties of perovskite quantum dots.By introducing other impurity ions,the photoelectric properties of the quantum dots can be controlled,and meanwhile the structural stability of perovskite can be improved.In the past few years,the technology of ion doping had been greatly improved.Many metal ions,including Bi³⁺,K⁺,Mn²⁺,rare earth ions(Ce³⁺,Tb³⁺,Yb³⁺)had been doped into the halide perovskite,and a series of excellent properties were obtained.(1)The band gap of CsPbI₃ was tunable by introducing Sn²⁺into CsPb I₃ quantum dots by thermal injection method.By adjusting the doping concentration of Sn²⁺and synthesis temperature,it was found that Sn²⁺can replace Pb²⁺,and the maximum red shift of the spectrum up to 40 nm with the increase of Sn²⁺concentration.At the same time,the band gap was reduced to 1.78e V,and that enlarged the application range.In addition,the synthesis temperature is also an important factor of Sn²⁺:CsPb I₃ quantum dots.The size of quantum dots increased by increasing the synthesis temperature.Due to the quantum confinement effect,the spectrum red shifted and the band gap becomed narrow.After that,the synthesized Sn²⁺:CsPb I₃ quantum dots were dispersed on the Ti O₂ thin film of FTO.Through the photocurrent testing,we found that the photocurrent of Sn²⁺:CsPb I₃ was stronger than that of pure CsPbI₃.Through the fitting calculation,Sn²⁺:CsPb I₃ had a higher electronic interface migration rate constant.However,in the process of exploring the stability of quantum dots,we found that Sn²⁺:CsPb I₃ had a red shift in the spectrum after storaging for a few days.It was found that some Sn²⁺were oxidized to Sn⁴⁺in the synthesis process.Some literature shows that Sn⁴⁺would reduce the carrier recombination rate.(2)We used a simple and feasible method,called one pot method,to synthesize CsPb Br₃ quantum dots doped with Zn²⁺and Cd²⁺.Through the method of doping heavily,the original bivalent Pb²⁺was partially replaced.We found that after doping,there were two peaks of blue light and green light.By increasing the doping amount of Cd²⁺and Zn²⁺and the synthesis temperature,we found that the intensity of blue light peak was enhanced and the red shift of green light peak was less.By adjusting the appropriate concentration,synthetic temperature,and the method of washing and centrifuging,we obtained almost pure blue light peak.On this basis,we selected the appropriate Zn:CsPb Br₃ quantum dots powder with blue and green peak as the phosphor,combined with red phosphor Ca Al Si N₃:Eu²⁺,with 395 UV lamp as the substrate,and prepared the white LED with the quantum efficiency of 11.89% without device optimization.