Study Of Planar Heterojunction Organic Photodetectors Based On Fused-ring Electron Acceptor Materials

Organic photodetectors have the advantages of light weight,good flexibility,simple preparation process,etc.,and have important applications in the fields of optical sensing and human body health monitoring.The new type of fused-ring electron acceptor materials with narrow band optical gap provides an important material basis for improving the detection ability of organic photodetectors in the infrared or near-infrared region.How to construct an organic photodetector with high sensitivity and good stability is the focus and difficulty of current study.Here we reported a planar heterojunction organic photodetector based on the non-fullerene fused ring electron acceptor material.We explored the photoelectric properties of organic semiconductors and the structure design of the photodetector and regulated the response spectral of the active layer and the light detection performance of the device.The main research results are as follows:(1)The conventional bulk heterojunction organic photodetector has the problem of the phase separation of the electron donor and acceptor,which has a great impact on the long-term stability of the device.In this work,a planar heterojunction organic photodetector based on fused-ring electron acceptor was constructed.The device structure was ITO/PEDOT:PSS/poly-TPD/ID-MeIC/C₆₀/BCP/Al.There was significant electron transfer at the interface of ID-MeIC/C₆₀ double-layer electron acceptor material,and poly-TPD as an electron blocking layer and hole transport layer not only promoted the effective dissociation of photogenerated excitons,but also greatly reduced the dark current density.The dark current density of the device at-0.1 V was reduced from 3.0×10^-6 A cm^-2 to 4.1×10^-7 A cm^-2.Compared with the conventional bulk heterojunction organic photodetector,the planar heterojunction organic photodetector exhibited better environmental stability.(2)By changing the thickness of the ID-MeIC/C₆₀ double-layer film,the optical field distribution in the device was tuned,and the response spectrum of the planar heterojunction organic photodetector in the ultraviolet-visible-near-infrared range was effectively adjusted.The optimized ID-MeIC(15 nm)/C₆₀(50 nm)structure device had a good linear dynamic range about 80 d B and specific detectivity at 745 nm was6.5×10¹⁰ Jones.(3)To further realize the narrow-band detection of the planar heterojunction organic photodetector,we deposited a 1?m thick P3HT light-shielding layer over the poly-TPD film by a spin coating method.The device based on ITO/PEDOT:PSS/poly-TPD/P3HT/ID-MeIC/PFN/Ag showed good narrow-band characteristics at?710 nm with a full width at half maxima of 107 nm,which maintained a good narrow-band response under-10 V bias.By tuning the optical band gap and absorption characteristics of the fused-ring electron acceptor,the position and full width at half maxima of the narrow-band response peak can be effectively tuned.By replacing ID-MeIC with ITIC,which has a larger optical band gap,significantly reduced the full width at half maxima of the narrow-band response peak to 83 nm,and specific detectivity of this device was?10¹⁰ Jones at-5 V.In addition,by reducing the thickness of the Ag to 10 nm and providing optical signals from both the ITO and Ag electrodes,a narrow-band spectral response of 620-750 nm and a broad spectral response of 350-750 nm were observed in the same device.