Synthesis Of Cesium Lead Halide Perovskite Nanocrystals And Their Applications In Photodetectors

Cesium lead halide perovskite nanocrystals(CsPb X₃,X=Cl,Br,I)exhibit great potential for applications in the fields of displays,lasers,photovoltaics and photodetectors due to their high absorption coefficient,size-tunable optical bandgaps and high photoluminescence quantum yield.The current research focuses on efficient synthesis of CsPb X₃ nanocrystals and tailoring their optoelectronic properties.In addition,it is still difficult to employ CsPb X₃ nanocrystals to develop photodetectors with high-efficiency light detection.Therefore,this thesis reports a method to tune the properties of perovskite nanocrystals during the chemical synthesis.The reaction precursors and ligands were used to tune nanocrystal sizes and chemical components,leading to UV-photodetectors with high-performance.The main research results and conclusions of this thesis are as follows:(1)Low-temperature synthesis of CsPb Br₃nanocrystals with Sn²⁺doping:Partial replacement of Pb²⁺with Sn²⁺in CsPb Br₃ nanocrystals resulted in tuning their optical properties.However,Sn²⁺is easily oxidized into Sn⁴⁺during the synthesis of CsPb_1-xSn_xBr₃ nanocrystals.In this thesis,low-temperature hot-injection method was demonstrated to synthesis CsPb_1-xSn_xBr₃ nanocrystals with uniform sizes.High-purity nitrogen protection and low-temperature reaction environment ensured Sn in the divalent state in CsPb_1-xSn_xBr₃ nanocrystals.The geometric sizes of the nanocrystals was reduced from?8.3 nm to?6.2 nm by changing the reaction temperature from 150^oC to 105 ^oC,and the photoluminescence spectral peaks showed a blue shift from 507nm to 488 nm.The reaction temperature of 135 ^oC led to a Sn²⁺-doping ratio of 3.4%in the perovskite nanocrystals.(2)Synthesis of blue-light-emitting CsPb Br₃ nanocrystals:Blue-light-emitting CsPb Br₃ nanocrystals suffered from low photoluminescence quantum yield and poor chemical stability,which limited their potential application in optoelectronic devices.In this thesis,the size of CsPb Br₃ nanocrystals was reduced to below 6 nm by increasing the content of acid ligands in the hot-injection method.The photoluminescence spectral peak of CsPb Br₃ nanocrystals showed a blue shift to 465nm and the photoluminescence quantum yield reached 30%.By doping a small portion of Cl(10%)into CsPb Br₃ nanocrystals,the photoluminescence spectral peak of the perovskite nanocrystals showed a further blue shift to 450 nm.(3)UV-photodetectors based on CsPb_0.966Sn_0.034Br₃nanocrystals:The interfacial defects in the photodetectors can trap photo-generated charges and then change the charge injection barrier at the interface to achieve photomultiplication effect.In this thesis,CsPb_0.966Sn_0.034Br₃ nanocrystals were introduced into the interface of the photodetectors.In the dark,the schottky junction barrier led to a small dark current,Whereas,the nanocrystals trapped photo-generated carriers under illumination,causing a large band-bending and thus a thin-enough barrier to allow electron tunneling from PVK to PC₆₀BM for photomultiplication effect.The photodetectors that combined the advantages of two conventional photodetectors(photodiode and photoconductor)obtained both low dark current and gain.The photodetectors at-7 V showed detectivities reaching 10¹¹Jones from 310 nm to 400 nm.The external quantum efficiency was 1940%at?340 nm,along with a responsivity and a response time of 5A/W and?1.16 ms,respectively.