Near-infrared Photodetector Based On D-A Polymer

Compared with monomer polymers,D-A polymers have the characteristics of strong intramolecular charge transfer ability,easy adjustment of spectral absorption and narrow band gap,which can effectively absorb light from visible to infrared.The organic photodetectors(OPDs)with near-infrared respond are currently widely used in biomedical imaging,vitro detection and machine vision and so an.Consequently,More and more D-A polymers have used to construct detectors to achieve near-infrared detection.However,narrow band gap polymers has the problems of energy level mismatch and high thermal noise.In this regard,reasonably design and application of polymers with appropriate energy levels and optimization of device structure are the two main ways to enhance the performance of OPDs.In this paper,several narrow-bandgap D-A polymers are selected to prepare a detectors with good near-infrared detection ability,and the performance of the devices is optimized by applying ternary mixing and defect-doped high gain structures.The polymer POTDPP was proved to be a good narrow band gap donor with excellent near-infrared absorption and energy level through absorption and electrochemical properties.Subsequently,a binary bulk heterojunction structure detector was prepared with it.Experiments show that the best acceptor is PC₆₁BM,and the best film forming process is:spin coating at 2500 rpm for 40 s,and then annealing at 60°C for 1 h.Then,devices were optimized based on ternary mixing POTDPP and PCE-10 or PBDTT-DPP.The feasibility and influence mechanism of ternary mixing are proved by absorption spectrum,carrier mobility,layer morphology and device performance.The best device has a maximum external quantum efficiency of 10.38%in the near-infrared corresponding to a wavelength of 890 nm;a response speed of microsecond;a near-infrared dynamic range of 103 d B;and a specific detectivity greater than 10¹³ Jones in the range of 660-848 nm.The performance of the device is close to that of a standard silicon detector,and it has excellent overall performance.The photoelectric characteristics,the density of defect states,and the change of relationship between the two over time illustrate the importance of defects in high gain.And through the absorption characteristics,defect state density and single-carrier transport characteristics,it is proved that HLZ defect doping has the functions of enhancing the absorption strength,increasing the defect state density and trapping electrons,thereby enhancing the gain effect of the device.What's more,the gain performance of the device was optimized based on the narrow band gap polymer PBDTT-DPP and HLZ doping,and an organic photodetector with high near-infrared response was obtained.The maximum external quantum efficiency in the near-infrared region of the obtained device under 1 V bias is 658%corresponding to a wavelength of 890 nm,and the specific detectivity is greater than 10¹³ Jones in the range of 738 to 838 nm,which has excellent near-infrared detection performance.