Research On The Fabrication And Performance Of Organic Photodetectors Based On Copper(Ⅰ) Thiocyanate As An Anode Interfacial Layer

Organic photodetectors,which can convert optical signals into electrical signals,have attracted much attention due to their great potential in the fields of optical communication networks,health monitor,image sensor and night vision.At present,the highest specific detectivity of organic photodetectors reported in the laboratory have exceeded 1.0×10¹⁴Jones,which meets the requirements of practical applications.However,most organic photodetectors are limited by the dark current density,the detectivity can not reach the above index.To solve this problem,this paper adopts CuSCN as the anode interface of OPD and systematically studies its mechanism for improving the performance of OPDs,providing a simple and efficient method to reduce the dark current density of OPDs.The work of this paper is mainly divided into four parts.In Chapter 2,CuSCN was chosen as the anode interface of the OPD,while NT40:IEICO-4F was used as the photosensitive layer to prepare the OPD.We systematically compared the influence of CuSCN and the widely used PEDOT:PSS interface on the performance of OPD.The mechanism by which CuSCN improves the performance of OPD was studied with various test methods,such as optical simulation,surface morphology analysis,and electrical performance analysis of the devices.According to the measurement results,CuSCN has an optical transmittance comparable to PEDOT:PSS,and it has a shallower conduction band bottom energy level.Compared to PEDOT:PSS-based OPDs,the dark current density of the CuSCN-based OPDs decreased to 6.7×10^-10 A cm^-2,and its detection rate reached 2.4×10¹³Jones,both of which exceeded the two key performance indicators of PEDOT:PSS-based OPDs.In Chapter 3,we designed and synthesized a thermally cross-linked hole transport layer,HT1,and constructed a CuSCN/hole transport layer bilayer interface to further improve the performance of the CuSCN-based OPD.We studied the cross-linking of HT1 through DSC and solvent resistance tests to ensure that the solvent of the photosensitive layer would not damage the thin film of the underlying hole transport layer.Experimental results showed that introducing a hole transport layer improved the contact between CuSCN and the photosensitive layer,which increased the hole transfer and extraction efficiency of the entire device,and was beneficial for improving the light responsivity of the detector.In addition,the CuSCN/HT1bilayer interface reduced the concentration of carriers and trap density of the OPD in the dark state,thereby reducing the dark current density of the OPD.Ultimately,the detection rate of the OPD was further improved,and a detection rate of 6.1×10¹³ Jones was obtained at 850 nm.These results suggest that CuSCN/HT1 can effectively improve the morphology and hole mobility of CuSCN films,providing a new method for further improving the performance of CuSCN.In Chapter 4,we used the organic small molecule material 7,7,8,8-tetracyanoquino-dimethane（TCNQ）doped with CuSCN to prepare a P-type doped anode interface and applied it to the OPD,significantly improving the detection rate of the detector.The doping concentration of TCNQ was only 0.03 wt%,but it visibly improved the surface morphology and mobility of CuSCN and increased its work function.According to the results of ultraviolet photoelectron spectroscopy（UPS）and Fourier transform infrared spectroscopy（FTIR）,electronic transfer and interaction occurred between TCNQ and CuSCN,indicating that they were not simply physically blended.The detector based on the CuSCN:TCNQ doped anode interface achieved a detection rate of 1.1×10¹⁴ Jones.In addition,we also performed universal tests on the CuSCN:TCNQ doped interface.The test results showed that regardless of whether it was in the fullerene or non-fullerene system,the CuSCN:TCNQ doped interface could improve the performance of the detector.This provides a simple and efficient method to improve the performance of organic light detectors based on CuSCN.In Chapter 5,we designed and synthesized perylene bisimide derivative PBI-DCOOH,and used it as a dopant to construct the CuSCN:PBI-DCOOH doped interface and applied it to the OPD.Compared to TCNQ,PBI-DCOOH has better solubility,which is more conducive to solution processing.The results of UPS and FTIR of CuSCN:PBI-DCOOH were similar to Chapter 4,indicating that they also formed effective p-type doping.The OPD based on CuSCN:PBI-DCOOH achieved a higher detectivity of 4.3×10¹³ Jones.The work in this chapter provides new ideas and methods for further improving the performance of CuSCN.