Study On The Preparation Of Copper-based Halide Cs₃Cu₂I₅ By Solution Method And Its Applications In Photodetectors

In recent years,perovskite materials in photoelectric detection have made great breakthroughs,among ultraviolet(UV)to visible band,because of the high light absorption rate,large carrier mobility,bipolar transport of carrier,and tunable bandgap etc.However,inevitable problems of toxic elements Pb in lead halide perovskites,which is harmful to the environment and the human body,and the instability of that,limiting its development in practical applications.Therefore,for the application view,research on lead-free perovskite materials is with more significance.In addition to the nontoxic and stable characteristics,such materials have excellent optical and electrical properties.Moreover,the large bandgap range of lead-free perovskites make it more suitable for the preparation of high-performance UV,even deep-UV photodetectors.Therefore,lead-free perovskites is undoubtedly a more suitable choice in the research of environmentally friendly perovskite-based UV photodetectors.In this work,copper halide Cs₃Cu₂I₅ is selected as the research object,and Cs₃Cu₂I₅ thin films were prepared by modified spin-coating strategy,and Cs₃Cu₂I₅nanocrystals(NCs)were synthesized by hot-injection method,and two kinds of Cs₃Cu₂I₅ synthesized by solution method are respectively applied to photodetection and their optoelectronic performances are studied.In the first part,we optimized the growth of Cs₃Cu₂I₅ films,including:the drop of anti-solvent,different temperature of thermal annealing.And then the crystal morphology,optical properties and the stability against heat,UV light and air/moisture of the materials were measured and analyzed.Subsequently,the metal-semiconductor-metal structure photodetector(MSM)based on Au/Cs₃Cu₂I₅thin films/Au were prepared and its photoelectric properties and operation stability were explored.At 5 V,265 nm light illumination,the responsivity of the device could reach to 17.8 A/W with the specific detectivity of 1.12×10¹² Jones and response time of 465/897?s.In the second part,because of the ultra-sensitive property to UV light of Cs₃Cu₂I₅films,we considered to integrate Cs₃Cu₂I₅ to Si to form a heterojunction to enhance the UV response of Si photodetector,and thus implement a UV-enhanced,self-powered photodetector.Experimentally,Cs₃Cu₂I₅ was directly spinning coating on the Si nanowires arrays(NWs)and built Cs₃Cu₂I₅/Si NWs p-n junction.It can be found that the response in UV region of Si NWs detector dramatically improved.At 0 V bias,under 265 nm light,the responsivity of such device can realize high responsivity of 130m A/W,the specific detectivity of 3.1×10¹⁰ Jones,and response time of 92.5/189.2?s.In the third part,considering the low specific detectivity of Cs₃Cu₂I₅/Si NWs heterojunction photodetectors caused by interfaces defects,the Si NWs-Cs₃Cu₂I₅ NCs composite structure was further designed and prepared.Firstly,we synthesis Cs₃Cu₂I₅NCs by the hot-injection method and then modified them on the surfaces of Si NWs,and realizing the passivation of defects through regulating Cs₃Cu₂I₅ replication surface ligands.The device structure of Si NWs-Cs₃Cu₂I₅ NCs can reach a significantly reduced dark current and thus realize a high sensitivity.At 0 V bias,265 nm light excitation,the specific detectivity of 2.1×10¹² Jones.Compared with Cs₃Cu₂I₅/Si NWs heterostructure photodetector,the detection performance is greatly improved.Due to the great stablility of Cs₃Cu₂I₅ NCs,the photocurrent of the device can still maintain more than 90%of the original value even after 300 days in the air ambient,while the dark current can be basically remained.In summary,it is found that the copper-based halide Cs₃Cu₂I₅ materials not only have a simple synthesis process and low preparation cost,but have excellent stability against thermal and humidity,which meets the application requirements of environment-friendly photoelectric devices.Considering the strong absorption capacity of UV light,it is expected to provide a feasible solution for the preparation of UV-enhanced broadband photodetectors.