Preparation Of Halide Perovskite And Its Application In Narrow Band Detector Design

Halide perovskites（HPs）typically exhibit an ABX₃crystal structure.Due to their extremely high photovoltaic conversion efficiency,they have garnered significant interest in the area of high-performance optoelectronic applications such as LED,photodetection,and catalysis.In the application of HPs as the core opoelectric active layer,narrowband spectral detector is extremely important because of its indispensable role in imaging,machine vision,biological diagnosis.Its narrow spectral response can effectively avoid the interference of other stray background light,so as to obtain more accurate and reliable results.However,when HPs materials were used to realize narrowband response in near infrared band,there is a contradiction that perovskite materials with near-infrared band response also have small bandgap and wide response spectrum.Therefore,special design of perovskite materials devices is required to realize narrowband response in near-infrared band.This paper focuses on narrow-band spectral detection of devices which HPs as photoelectric active layer.Firstly,we adjust the carrier recombination rate and spectral absorption characteristics of perovskite materials by doping organic dyes in order to achieve narrowband detection in near-infrared region.Then,in order to overcome the drawback of dye doping in our first work,such as low detection rate,complex device technology and poor stability of active layer,We began the second work to explore the vertical device structure itself so as to achieve narrowband detection without doping and damaging the excellent optoelectronic characteristics of perovskite.Finally,combining with the planar optical waveguide effect and the absorption characteristics of perovskite,we could achieve narrowband detection without doping and damaging the perovskite.Furthermore,we also use quantum dots which have better thermal stability and low lead toxicity as the active layer to realize narrowband detection based on the planar waveguide effect.In the realization of narrowband detection and future applications,the disadvantages of stability of perovskite becomes prominently.Here,we use the two-dimensional material（PEA）₂Pb I₄ with better stability as the photoactive layer to solve the stability problem.The ferroelectric effect is used to realize the self-powered response of 2D material devices,which improves the weak response of 2D material.Our findings represent a significant advancement towards realizing practical applications of PPDs.Key outcomes of the study include:（1）We adjusted the absorption of the photoresponsive layer by doping with Rhodamine 800 during the preparation of perovskite.This enhance the absorption coefficient for long-wavelength spectra and reduced the range of low-absorption regions,thereby enabling narrower narrowband detection through the utilization of the carrier collection narrowing（CCN）effect.Dye doping alters the formation of perovskite,resulting in smaller perovskite grains and increased contact area at the grain boundary.The incorporation of impurities induced by this process creates a significant number of trap state levels,leading to increased carrier recombination rate and reduced mobility and diffusion distance of carriers.All these change makes it possible to suppress the collection of short-wavelength photocarriers by carrier collection narrowing at the thickness of conventional spin-coated films（300-500 nm）,thus realizing extremely narrow detection in the near infrared region（FWHM<60nm）.We elucidated the narrowband detection mechanism of thin-film PPDs and further narrowed the detection range by selecting suitable doping materials,enhancing the anti-interference ability in various applications such as biomedicine diagnostics..（2）By studying the refractive index of each functional layer of traditional vertical thin film devices,we found that they have a planar optical waveguide（PLC）structure.On the basis of the PLC structure of perovskite thin film devices,we realized narrowband spectral detection by taking advantage of the transverse propagation of incident light in the device and the absorption characteristics of perovskite material itself based on the carrier collection narrowing effect.By synthesizing different composition perovskite thin films with different response spectral ranges,the narrowband detection coverage in the near-infrared region from750nm to 1000nm is realized,and all the narrowband response is 25-80nm in full-width at half-maximum.The narrowband detector design that utilizes the lateral propagation of light has the characteristics of high integration,strong scalability,and no damage to the perovskite layer,and has broad application prospects.（3）The traditional bulk material HPs material is easy to decompose under photothermal conditions and lead toxicity problems,we used tin lead alloy quantum dots（QDs）Cs Sn_0.5Pb_0.5I₃ as active materials here.This alloy quantum dot reduces the amount of toxic lead and has a smaller band gap which has a larger spectral response range（up to 890 nm）than lead-like.However,due to the easy oxidation and low vacancy energy of Sn²⁺in perovskite,the Cs Sn_0.5Pb_0.5I₃ alloy QDs prepared are easy to form tin vacancy defects.Here,we take advantage of the comproportionation reaction between tin power and tetravalent tin,to effectively reduce the oxidation of Sn²⁺in the process of Sn I₂ heating dissolution and formation of precursor,as well as the oxidation product Sn⁴⁺of materials itself by adding tin powder in the precursor during the preparation.The improved preparation of Cs Sn_0.5Pb_0.5I₃ QDs effectively reduces the internal defects caused by tin vacancy,improves the crystal quality and stability,also the success rate of preparation of tin-lead alloy QDs is greatly increase.The QDs show excellent performance when they are fabricated into photodetector devices,the detectivty is 1.5′10¹²jones and the response speed is 79μs.In a similar vein,narrowband detection can be realized in PPDs that employ QDs as the photoresponsive layer,which rely on the PLC structure of the PPDs.（4）Due to the stability problem of traditional perovskite material（3D）devices,which has been preventing its real application in commercial applications,we began to focus on the two-dimensional（2D）perovskite material PEA_n+1Pb_nI_3n+1 with better stability of periodic organic molecular layer to try to replace bulk materials.However,the poor electrical conductivity of organic cations makes the photoelectric response of pure two-dimensional materials low.In this work,we prepared a two-dimensional perovskite film of PEA₂Pb I₄（n=1）.The ferroelectric properties of the two-dimensional material were utilized to polarize the film on the transverse electrode by illumination and bias,so that the organic cations and halogen anions in film material would have sustained polarization orientation and generate corresponding induced charges at the electrode which form built in potential.After the removal of the external bias,the built in potential in the opposite direction of the bias is retained in the transverse device.This built in potential helps the photocarrier to separate and reach both sides of the electrode to form a response current,which effectively decrease the disadvantage of large exciton binding energy caused by the periodic organic layered quantum well structure of two-dimensional materials.We achieved self-driven photoelectric response on a transverse detector with electrode spacing of200μm.The detectivity is 4.2′10¹² jones at the highest response wavelength.After the ion polarization orientation in the 2D material is restored,the bias polarization can be carried out again to make the detector device reach the best response state again.The photodetector accomplish by this method not only has the excellent photoelectric response ability of perovskite material but also has the excellent stability.Therefore,it has great potential to replace 3D perovskite material as the mainstream optoelectric response active layer in the future commercial applications...