The Construction And Performance Of Solution-processed Low-dimensional Semiconductor Materials Based Photodetector

Photodetector is the key component of transformation from optical signal into electric signal,and has been widely used in various fields such as environmental monitoring,industrial production,optical communication and imaging,etc.It has already become the critical research point.Traditional photodetectors were fabricated mainly by vacuum process,which can not meet the development trend of flexible and wearable optoelectronic devices because poor compatibility with flexible,especially fibrous substrates.Fortunately,solution process can solve the above problems.The solution process possesses obvious advantages such as ease of large-area construction,compatible with flexible,elastic or even fibrous and other complex substrates,and low-cost,showing huge potential in the applications of optoelectronic devices for the low dimensional materials.However,all-solution-process based photodetectors are rarely reported.In addtion,the problems of compatibility between different solution process,film quality and interface contact remains to be promoted.This dissertation adopts full solution technology constructing all-printed flexible photodetector and fiber-shaped self-powered photodetector based on ZnO low-dimensional structure material with excellent photoelectric performance.In addition,high-performance CsPbBr3 photodetectors are fabricated using solution process,and the detective performance is further improved through the local surface plasmon resonance(LSPR)and other method,and the mechanism is clarified.The main research results are summarized as follows,(1)All-inkjet-printed flexible ultraviolet(UV)photodetector based on ZnO quantum dots(QDs).Inspired by the superior optoelectronic properties of ZnO in UV spectrum,here for the first time,the all-inkjet-printed ZnO photodetector with low-temperature post-processing is demonstrated.The ZnO QDs were synthesized via room-temperature sol-gel method,the printable nanoink was then obtained by mixture certain ratio of solvents.The high-quality ZnO QDs thin film with root-mean-square(RMS)roughness of only 1.21 nm was assembled via inkjet printing and UV treatment.The best device performance with on/off ratio exceeding103 and response time less than 0.3s was obtained at the same time.The flexible device is also displayed with great flexibility,it can operate normally under bending states,and the detective performance remain stable after 500 bending cycles.The research of all-printed ZnO photodetector shows huge potential of solution-processed flexible optoelectronic devices.(2)Self-powered omnidirectional fiber-shaped UV photodetector based on ZnO nanorods(NRs)array.The ZnO NRs array on Zn wire was synthesized by hydrothermal process with high crystallinity,compact and uniform morphology.The photodetector is fabricated using all-solution process with structure of Zn/ZnO/PVK/PEDOT:PSS/CNT.In this device,the p-n junction is formed between PVK and ZnO,leading to a built-in electric field.The PEDOT:PSS act as hole transporting layer and contributes to the quick transport of holes.In addition,PVK and PEDOT:PSS are polymers,forming good coating on ZnO nanowires array thus the interface contact of the device was improved.Based on these characteristics,this photodetector shows on/off ratio of2 under325 nm laser illumination with no external bias,and could steadily work under different bending states with almost no deterioration.The maximum responsivity of9.96 mA/W is stable under omnidirectional incident light(0-360°)due to advantage of fiber shape.Moreover,it could still work normally after continuous bending for more than 100 cycles,and the attenuation of photocurrent is less than 4%.This fiber-shaped UV photodetector plays an exemplary role in constructing flexible,self-powered and wearable photodetectors.(3)High-performance all-inorganic visible photodetector via synergetic enhancement of preferred orientation and plasmonic effect.The CsPbBr3 nanocrystals(NCs)ink is synthesized using low-temperature recrystallization method.By means of contrifugal-casting,the preferred-orientation CsPbBr3 film was obtained,the photocurrent of the device has improved from 0.67?A(drop-casting)to2.77?A.On the basis,combined with the finite-different time-domain(FDTD)computing simulation,the light absorption ability of CsPbBr3 is increased after introducing near field enhancement effect of localized surface plasmon resonance(LSPR),thus on/off ratio of the device is increased from 1.6×105 to 106,and the photocurrent is further promoted from 245.6 ?A to 831.1 ?A,showing an enhancement factor of 238%.(4)High-performance visible photodetector based on two-dimensional perovskite nanosheets(NSs).The CsPbBr3 NSs was synthesized under room temperature with high crystallinity,good dispersion and uniform morphology.And photodetector achieving high external quantum efficiency closing to 100%can be obtained by drop casting.Then the device performance of visible photodetectors based on different volume ratio between Au NCs and CsPbBr3 NSs were compared.The best detective ability was obtained when the volume ratio of Au NCs is 5%,and the linear dynamic range(LDR)can reach 120 dB.The effect of Au NCs is mainly two aspects.On the one hand,the absorption is enhanced and spectral response range is broaden due to LSPR.On the other hand,the energy transfer takes place between Au NCs and CsPbBr3 NSs,which promots the seperation of photo-generated electron-hole pairs thus improving photocurrent.Moreover the response speed is faster as the decay time decreased from 0.304 ms to 0.138 ms.The study of perovskite photodetector could lay the foundation of both theory and experiments for practical application of perovskite photodetectors.