| Modern society is an information society,and the development of information technology has an important strategic position to improve people's living standards.The photodetector receives light radiation,and transform the photoelectric current into electrical signal that easy to be processed and operated,and provide base signal of photoelectric sensor.Otherwise,the subsequent information transmission and information processing are like passive water.As far as photoelectric detection technology from visible light to near infrared band is concerned,its application covers various fields such as image sensor to face recognition,environmental monitoring,military infrared guidance,infrared remote sensing,nondestructive flaw detection,material analysis,etc.Visible-near infrared detector has irreplaceable function.Compared with inorganic detectors,photodetectors based on organic semiconductor materials have the advantages of solution processing and adjustable optical and electrical characteristics.With the emergence of non-fullerene small molecule receptors,detectable bands cover visible light and near infrared regions.However,there are relatively few reports about excellent performance of various parameters,near infrared response and limiting factor analysis.The first part of this doctoral dissertation focuses on the analysis and demonstration of the reasons for the performance improvement of photodetectors from the perspectives of injection barrier,noise,exciton dissociation and photocurrent formation constraints by using new small molecule receptors and combining different device structures and optimization conditions.The degree applicant selects two materials with complementary absorption.PBDTTT-C-T?conjugated polymer based on benzothiophene benzo[1,2-b:4,5-b']dithiophene unit?with wide band gap electron donor material is blended with FOIC?fused octacylic?with narrow band gap to form bulk heterojunction.Combined with the measurement results of electron energy level,electroluminescence and photoluminescence,it is confirmed that the system has efficient photo-induced electron transfer and hole transfer channels,thus realizing a wide spectral response covering the range of 350-950 nm from ultraviolet-visible-near infrared?short wave?.The influence of the traditional positive structure and the inverted structure on the device performance is studied and compared.It is found that the electron injection barrier of the inverted device is increased from 0.88 e V to 1.48 e V.Under the bias voltage of-1 V,the dark current density can be effectively reduced by two orders of magnitude to 8.3×10-10A cm-2.The device has the characteristics of large parallel resistance and low thermal noise by using a thicker photoactive layer.Using Fourier spectrum analyzer,the total noise current of the device is determined to be as low as 10-14 A Hz-1/2,noise signal.According to this,it can be calculated and determined that the specific detection rate of the device is above 1×1013 Jones at 430-920 nm.At the same time,the study also measured and determined that the linear dynamic range of the detector is 106d B.The rising and falling time are 12?s and 14?s respectively.The cut-off frequency of-3 d B and-6 d B are 30 k Hz and 60 k Hz respectively.Meet the requirements of image-level sensors and can realize distinct imaging.In the second part of this doctoral dissertation,the factors affecting the performance of photodetectors based on pyrazine PTQ and isoindigo PTIIG are explored.By adjusting the height of Schottky barrier junction,using non-fullerene receptors with different characteristics and using additives,and combining with capacitance-frequency measurement,degree applicants analyzed and studied the influence of dielectric constant and energy level distribution on device performance.The research focuses on the prospect of preparing high-performance near-infrared photodetectors based on isoindigo derivative PTIIG-DTO.The dielectric constant of the material is as high as 12,and the exciton binding energy can be as low as 50 me V in theory,thus providing an ideal research system for preparing photodetectors based on metal-organic semiconductor heterojunctions.Through the preparation of Schottky barrier junction devices based on a single pure phase material as the photoactive layer,it is found that its detectable optical response is in the range of 600-1600nm,and its external quantum efficiency is 0.18%at 1000 nm,which is 1-2 orders of magnitude lower than that of bulk heterojunction devices based on donor,but still reaches one of the best levels of similar devices.The reason why the performance of bulk heterojunction system composed of high dielectric constant PTIIG-DTO and electron acceptor HJF5 deviates from the expected value is studied and analyzed.After defect analysis,it can be confirmed that there are certain deep level defects in PTIIG-DTO,and free carriers will be trapped by these defects to form SRH?Shockley-Read-Hall?recombination,resulting in loss of photo-generated current.Based on the performance of the photodetector of this system,it is found that by introducing 0.5%additive into the solution,the morphology of the active layer can be optimized,the energy disorder degree of the band tail can be reduced,and thus the density of deep level defects can be reduced.The third part of this doctoral dissertation focuses on the realization of optical detectors with optical band selectivity.This part of work is based on a series of near infrared responsive electron donor polymers and traditional electron acceptor materials PCBM or new narrow band gap electron acceptor materials.The research work explored the influence of electron acceptor content,device structure,different system to acceptor ratio,active layer thickness,electrode interface buffer layer and other factors on the optical band selectivity of photodetector.Through comprehensive optimization of the above influencing factors,narrow spectral response near infrared detectors with specific detectivity of 2×1011 Jones have been realized in PBTTT-C-T:ITIC system and PDPP3T:Y6 system.The full width at half maximum of both detectors is 50nm,the response peak of the former is 800 nm,and the response peak of the latter is 940 nm.The performance of the obtained optical band selective photodetector reaches one of the best levels of similar devices. |
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