Study On The Growth Of Inorganic Halide Perovskites And Their Photodetection Properties

Photodetectors that convert incident optical signals to electrical signals are essential in a wide range of applications,including medical analysis,security surveillance,optical communications,and biological sensing.Commercialization prospects are high for photodetectors with good responsivity,fast response speed,low power consumption,good stability,and low processing cost.Among the various semiconductor materials explored for photodetectors,the newly emerging perovskites have attracted considerable attention due to their excellent properties such as tunable bandgap,high and balanced electron/hole mobility,long carrier lifetime,large carrier diffusion length,and simple processing technique.In addition,the device performances of perovskite photodetectors have rapidly improved over the past few years in terms of material synthesis,electrode optimization,interface modification,and device structure.However,although the performance of the device based on organic-inorganic hybrid perovskite photodetector has made great progress,the problem of instability hinders its further application.To solve this problem,all-inorganic halide perovskite materials are a good choice.Among them,Cs+ has an ionic radius(1.81(?))similar to CH3NH3+,which is an effective way to improve stability.Under these circumstances,we prepared all-inorganic halide materials through different methods such as solution method,vapor phase method,and anti-solvent crystallization,and studied its material characteristics,photoelectric properties,and stability.The main works and innovation of the paper are summarized as follows:1.A dense CsPbBr3 thin film was successfully prepared by the solution method,and its structure and optical properties were studied in detail.Then a metalsemiconductor-metal photodetector were prepared using the CsPbBr3 thin film as a light absorption layer,and the photodetection performance was further studied.Photoresponse analysis shows that the effective detection of 405 nm light is achieved in the device,which can achieve a high responsivity of 55 A/W and a fast response speed of 430/318μs.2.The CsPbBr3 microplatelets was successfully prepared by using the chemical vapor phase deposition(CVD)technique,which solved the relatively poor carrier transport ability and instability of poly crystalline film caused by the existence of a large number of defects and grain boundaries.The stability of the microplatelets to light,heat and humidity environments has been studied.Compared with the organic-inorganic hybrid perovskite and polycrystalline film,the stability of all-inorganic microplatelets has been greatly improved.Then,it was placed to the interdigital electrode by wet transfer method to prepare a photodetector device,which proves that the microplatelets photodetector without encapsulation has long-term working ability,heat resistance and recoverability.3.Combining the advantages of adjustable band gap,Cl is used to replace Br and a high-quality wide band gap CsPbCl3 micro-wire network structure was prepared by CVD method.By adjusting the temperature and reaction time of the process,a series of micro-wire network structures with different sizes and different coverages can be obtained.The material has a long carrier lifetime,which is conducive to carrier transmission and collection.On this basis,an ultraviolet(UV)photodetector targeting 2 00-420 nm was prepared,and the responsivity could reach 14.3 mA/W.4.Although the performance of photodetectors based on all-inorganic lead-based perovskites has been improved,the toxicity of lead limits its further application,so replacing lead with low-toxic metal cations can solve this problem.Among them,the double perovskite Cs2AgBiBr6 possess non-toxic,stable,excellent electrical and optical properties,and therefore have great potential for the preparation of highperformance photodetectors.In the experiment,the optimized thin film was combined with GaN thin film to fabricate a type Ⅱ heterojunction photodetector.The device is sensitive to light illumination with wavelength of 200-550 nn,and the stability of Cs2AgBiBr6 material and device has been tested.The results prove that it has the ability to endure a high temperature of 373 K for 10 h continuous running,demonstrating a good temperature resistance.In addition,after 3-month storage in open air,the photodetection capability of the device can almost be maintained.The above results indicate a remarkable stability of the Cs2AgBiBr6 films against environment oxygen/moisture,light and heat,and are also evident of the reliable Cs2AgBiBr6 light absorber compatible for practical applications under harsh conditions.5.On the basis of the above research,the non-toxic and stable Cu+ was used to replace the toxic Pb2+to prepare a wide band gap Cs3Cu2I5 thin film.Solutionprocessed lead-free Cs3Cu2I5 films were used as the light absorber to fabricate spectrum-selective UV photodetectors by using the charge collection narrowing(CCN)concept,overcoming the shortcomings of conventional strategies for making narrowband photodetectors,and a narrow response "window"of 300-370 nm was achieved.In addition,lead-free Cs3Cu2I5 is very stable against heat,UV light,and environmental oxygen/moisture.Typically,the unencapsulated device can endure a high working temperature(373 K)for 12 h continuous operation in ambient air.Further,UV imaging applications were demonstrated by deploying the photodetectors as sensing pixels.and the results proved that the device can reproduce the original pattern with high fidelity.6.As a member of the Cu-based halide perovskite,CSCU2I3 also exhibits good photoelectric properties and intrinsic absorption of UV light,and the one-dimensional chain-like structure is beneficial to the efficient transmission of the carrier along the Cu-I polyhedron.The CsCu2I3 nanowires(NWs)with wide bandgap were prepared by antisolvent engineering,and the width and length of the CsCu2I3 NWs can be adjusted within a large range from the nanometer(56 nm)to the micrometer(6.0 μm)scale by changing the dropping speed of antisolvent.Here,for the first time,ternary copper halide CsCu2I3 NWs were used as the light absorber to achieve polarization-sensitive UV photodetection.By combining the intrinsic anisotropy of the asymmetric structure and external morphology anisotropy of CsCu2I3 NWs,a record photocurrent anisotropy ratio of-3.16 was achieved.Owing to the high crystallinity of the CsCu2I3 NWs,the device exhibits remarkable photodetection ability with a responsivity of～32.3 A/W,a specific detectivity of 1.89×1012 Jones,and a fast response speed of 6.94/214μs.Moreover,such a device fabricated on a flexible substrate shows almost no photodetection degradation after extreme bending for 1000 cycles,demonstrating good flexibility and bending endurance.The results obtained highlight the great potential of such copper halides as a stable and environmentally-friendly candidate for polarization-sensitive UV photodetectors,rendering them potentially useful for assembly of optoelectronic systems in the future.