Research On Photoelectric Properties Of Three-phase Heterojunction Organic Photodetectors

Organic photodetectors(OPDs)have many advantages,such as many types of active layermaterials,adjustable absorption wavelength range,light materials,simple preparation process,low cost,and large absorption coefficient.In the light detection field has a good application prospects.The research in this dissertation is based on the organic photodetectors in the image sensor.Therefore,it is necessary to study the balanced photoelectric properties of the three primary colors of the device.Based on the P3HT:PCBM system,this paper solves the problem of weak red light response and enables the device to achieve the balanced response of three primary colors to meet the requirements of the image sensor.First of all,for the balanced absorption of blue-green light in the P3HT:PCBM system,the thickness of the organic active layer and the mixing ratio of the device to the receiver are optimized,so that the device achieves balanced responses of blue-green light.The buffer layer is then used to modify the electrode and active layer interfaces to improve device performance.The results show that the device structure using ITO/PEDOT:PSS(35nm)/P3HT:PCBM(200nm)/Li F(1nm)/Al while the device can be achieved balanced responses of blue-green light.The blue-green photoelectric characteristics of the device:blue responsivity is 185m A/W,specific detectivity is 2.0×10¹¹Jones;green responsivity is 196m A/W,specific detectivity is2.1×10¹¹Jones.After the device is optimized,the blue-green photoelectric characteristics are evenly distributed,that is,the balanced response.Compared with the previous P3HT:PCBM system,the device exhibits the advantages of two-color equalization detection.Then,on the basis of the above,the red light absorbing material PBDT-TT-F is incorporated to make up for the shortcomings of insufficient red light response of the P3HT:PCBM system and to enable the device to achieve a balanced response of three primary colors.The structure adopts ITO/PEDOT:PSS(35nm)/P3HT:PCBM:PBDT-TT-F(200nm)/Li F(1nm)/Al,and P3HT:PCBM:PBDT-TT-F is prepared as 12:8:1.12:8:2,12:8:3,12:8:4,12:8:5 Five sets of devices.By the J-V characteristics and AFM analysis,PBDT-TT-F can promote the surface crystallization of the active layer,so that the surface bulges and the roughness becomes large.Therefore,the red light absorbing material not only broadens the absorption spectrum of the active layer but also acts as a solvent additive.After the deviation analysis on the characteristics of the five groups of devices,the results showed that the electrical characteristics of red,green and blue light at the ratio of 12:8:3:the responsivity is 470m A/W,the specific detectivity is6.5×10¹¹Jones,and the responsivity is 381m A/W,specific detectivity is 5.3×10¹¹Jones;responsivity is 450m A/W,and specific detectivity is 6.3×10¹¹Jones.The deviation of the photoelectric responses of the three primary colors is the smallest,that is,the three-primary color photoelectric characteristics are uniformly distributed,and the balanced response of the three primary colors is achieved.Finally,the linear dynamic range,quantum efficiency and transient response of the optimal device are analyzed.The best dynamic range for the three primary colors of the device is 50,48,and 48,respectively.Quantum efficiency results show that the quantum efficiency is too high.This article explained by the electron trap assisted hole injection model:electron formed after exciton dissociation accumulate at the cathode buffer layer and PBDT-TT-F interfaces,making the energy band bend downward and decrease the hole injection barrier.At this time,the response current includes the injection current and photocurrent,and the phenomenon of high quantum efficiency occurs.Transient response was measured:rise,fall time of red,green and blue(76?s,380?s),(48?s,340?s),(48?s,316?s).The rising and falling time of red light is relatively long,and the amount of red light material is small and is distributed in the entire active layer space.Therefore,it takes a long time for charge accumulation and release.Compared with the existing research,this paper has the advantage of balanced response of three primary colors,and provides ideas for developing organic photoelectric detectors for CMOS image sensors.