Preparation Of Electron Barrier Layer And Research Of Device Performance For Organic Photodetectors And Its Imaging Application

Compared with inorganic detectors,organic photodetectors（OPDs）have the advantages of higher light absorption coefficient,adjustable response spectrum,flexibility and low temperature process.OPDs have attracted extensive attention and are more suitable for low-cost and large-area image sensor.At present,although the research of OPDs has made remarkable progress,there are still limitations of large dark current and insufficient detection.In this paper.the electron barrier layer is researched to reduce dark current of inverted organic photodetectors.By synthesizing p-type inorganic nano-materials and introducing it into heterojunction OPDs,the dark current of the device is reduced and the response of the device is improved.The device manufacturing at low/room temperature is realized.Finally,OPDs device and TFT array are integrated,and the application of image sensor and X-ray plate detector based on organic photodiode is explored.1)The p-type Ni O_x nanomaterials with average particle size of 5-10 nm were prepared by hydrothermal treatment of Ni C₂O₄·2H₂O nanoparticles as the precursor of thermal decomposition.The Ni O_x electron barrier layer prepared by low temperature solution process on the organic active layer in the inverted organic photodetector and can effectively block the injection of external charge to reduce the dark current of the device.The dark current density of the device is 1.13×10^-7 A cm^-2（-5 V）,which is more than one order of magnitude lower than that of organic photodetector without electron barrier layer.Ni Ox thin film was introduced into a top-illuminated flexible organic photodetector,and the flexible device maintained a good light response at 3 mm bending radius and 60,000 bending times,respectively.2)The p-type CuCrO₂ nanoparticles with average particle size of 10-15 nm were prepared by one-step hydrothermal synthesis at 220℃for 12 h.The dispersive properties of nano CuCrO₂ in different solvents were studied,and the affinity between dispersed materials and organic films was tested by contact Angle.It was found that isopropanol dispersed materials were more suitable for preparing good quality films on organic materials.An inverted top-illuminated organic photodetector with semi-transparent silver metal electrode was prepared by using p-type CuCrO₂ material as an electron barrier layer.Except for the electrode,the other layers were prepared by low-cost room-temperature solution method.The device dark current density is 6.48×10^-8 A cm^-2（-5 V）.Compared with the traditional evaporation of Mo O₃electron barrier,the one-step synthesis of nanomaterial and the room-temperature solution method have obvious advantages in the fabrication of inverted organic photodetectors.3)PEDOT:PSS-CuCrO₂ composite transparent electrode was prepared by doping CuCrO₂nanomaterial.The transmittance and REDOX ability of the thin film electrode doped with different concentration were tested.It was found that a small amount of CuCrO₂ doping（1-6wt%）had little effect on the transmittance of PEDOT:PSS films in the 300-800 nm range,and could improve the activity and charge collection capacity of films.The influence of different concentration of doping electrode on the performance of top-illuminated photodetector was studied.The device has a dark current density of 4.12×10^-8 A cm^-2（-5 V）.At the same time,the nonlinear response of the device under low light is investigated,and it is considered that a small amount of photogenerated charge under low light needs to overcome the built-in electric field of the device,which leads to the nonlinear response of the device.4)On the basis of the first two works,the organic photodetector and TFT array substrate are integrated to realize the image sensor.Through the imaging test of spatial resolution,low-light imaging ability and different detailed patterns,it is proved that the image sensor has a relatively complete ability to present objects.The scintillator film was placed on the organic image sensor,and the prototype of indirect X-ray flat plate detector based on organic photodetector was developed.The X-ray fluoroscopic imaging capability of the detector was verified by imaging ballpoint pen and PCB board.Therefore,organic photodetectors are expected to be applied in the field of flexible wearable electronics and medical imaging technology in the future.