Study On The Cs-Pb(Cu/Sn)-Br Perovskite Quantum Dots With Synthesis,Stability And Optical Properties

In recent years,all-inorganic perovskite quantum dots(QDs)have been rapidly developed as a typical semiconductor nanomaterial.The perovskite QDs have shown great application potential in many fields such as lighting display,photovoltaic conversion,and photoelectric catalysis,relying on the characteristics of high quantum efficiency,fewer inter-band defects,fast carrier transmission speed,and adjustable band gap.However,the Pb-based perovskite has serious shortcomings in terms of biocompatibility and stability,and its application in the field of photoelectron catalysis is rarely reported.Therefore,the cation-doped is used to reduce the toxicity of perovskite QDs,encapsulate the Si O₂shell to improve its stability,encapsulate white LEDs and construct photoelectric catalytic devices to expand its applications.The specific research contents are as follows:(1)The Cu⁺/Cu²⁺doped Cs-Pb-Br-based perovskite QDs were synthesized by room temperature crystallization method to reduce the toxicity of lead-based perovskite.Due to the change of the Pb/Cs ratio,Cu⁺doped quantum dots produce a transition from Cs Pb Br₃to Cs₄Pb Br₆phase.The PL peak of the perovskite QDs gradually blue shifts with the increase of Cu⁺concentration,and a blue PL peak appears at 435 nm.It is found that the blue emission of Cs Pb Br₃:Cu⁺and Cs₄Pb Br₆:Cu⁺QDs still maintains exceed 50%of PL intensity after 90minutes in pure water,which proves that they have excellent water stability.Unlike the doping of Cu⁺,the doping of Cu²⁺does not affect the crystal structure of the perovskite.But the PL peak of perovskite gradually blue shifts and the PL intensity first increases and then decreases with the increase of the doping amount.The fluorescence lifetime of Cu²⁺doped quantum dots decreases with the increase of the doping amount due to the quenching effect of excessive Cu cations.To improve the water stability of Cs Pb Br₃:Cu²⁺QDs,the Si O₂shell is coated on it for surface modification.The synthesized Cs Pb Br₃:Cu²⁺@Si O₂QDs have both excellent optical properties and significantly improved water stability.(2)Since Sn²⁺is widely used in organic-inorganic hybrid perovskites,the synthesis and performance of Sn²⁺doped Cs-Pb-Br-based perovskite QDs have been discussed.With the increase of Sn²⁺concentration,the phase of quantum dots also changed from Cs Pb Br₃to Cs₄Pb Br₆.The PL spectrum and absorption spectrum both show a trend of red shift first and then blue shift owing to the increase in defects caused by Sn doping and the passivation of the crystal surface after the appearance of the mixed phase.In addition,a blue emission peak appears at 433 nm when the doping amount exceeds 50 at.%.In order to improve the water stability of quantum dots,small-size single-pair single-coated Cs Pb Br₃:Sn@Si O₂ and Cs₄Pb Br₆:Sn@Si O₂ core-shell QDs were prepared by a one-step synthesis method.After 24 h of aging reaction,the PL intensity of the core-shell QDs were 46.7%and 59.6%of the initial value,while the uncoated QDs had been completely quenched.However,the air stability of Sn²⁺doped perovskite QDs is insufficient owing to Sn²⁺is easily oxidized.In response to this problem,the Cs₂Sn X₆(X=Cl,Br,I)lead-free perovskite material was synthesized by thermal injection technology,and the full chromatographic emission from 436 nm to 808 nm was achieved.Based on this,using improved coating technology,a Cs₂Sn I₆@Si O₂ composite material with excellent water stability was synthesized in 1-octadecene after ice bath.(3)For the application of Pb-based perovskite,we mixed Cs₄Pb Br₆ QDs and Gd₂O₃:Eu phosphors to fabricate a white LED,which has a color coordinate of(0.33,0.34)and a color temperature of 5752 K.Subsequently,Ti O₂,Cs Pb Br₃,and Ni O were used as the electron transport layer,light absorption layer,and catalyst to construct a photoelectric catalytic device.To improve the water stability of the device,hydrophobic carbon slurry and graphite were selected as the hole transport layer.The solution spin coating method,spin Cs Pb Br₃ QDs toluene solution and PLD technology were used to construct FTO/Ti O₂/Cs Pb Br₃/C/Ni O photoelectric catalytic devices,and the preparation process of the solution spin coating method was explored.The device constructed by the solution spin-coating method has a higher current density,but the current density increase is not obvious under light,while the other two methods can obtain a more obvious light response,but the current density is extremely low.