Research On Near-infrared Photodetectors Based On Organic Materials And Their Arrays

As a kind of device that converts specific optical signals into electrical signals,photodetectors are widely used in military and daily life.In recent years,organic photodetectors(OPDs)have attracted increasing attention from researchers due to their advantages of the solution-based fabrication process,large-area fabrication potential,light weight and tunable bandgap.At the same time,near-infrared light has the characteristics of being invisible to human eyes,strong penetration and non-destructive.It plays an irreplaceable role in the fields of optical communication,medical imaging,intelligent unmanned driving,environmental monitoring and so on.Therefore,near-infrared OPDs have become one of the research focuses of optoelectronic devices.In the past decades,for near-infrared OPDs,researchers have made many efforts in the synthesis of low-bandgap materials,precise matching of donor-acceptor energy levels,and interfacial engineering of devices.However,many application fields in the current society require the integration and arraying of multiple detection units,the development of only single near-infrared OPDs is not enough to meet the practical needs.In response to the above problems,this thesis mainly carries out the following two parts:First,we selected different non-fullerene acceptor materials to prepare and optimize three kinds of near-infrared OPDs.In this section,the experimental optimization process and intrinsic working mechanism of one of the OPDs are described in detail.The effects of the electron transport layer,the hole transport layer and the active layer on the device are explored.Then a detailed performance measurement,characterization and comparative analysis of various near-infrared OPDs are carried out.The measurement results show that the near-infrared OPDs prepared with the PTB7-TH:FOIC active layer have the best overall detection performance,with a dark current density of 1.68×10^-6 A cm^-2 and a noise current of 2.67×10^-12 A Hz^-1/2,with a high specific detectivity(D*)of 3.26×10¹⁰ Jones in the near-infrared region(wavelength of 850 nm).In addition,the device also has a response speed as fast as5.68?s.The other two near-infrared OPDs have a wider detection range in comparison,and have a good response in the region of wavelengths greater than or equal to 950 nm.This work explores the material selection and preparation optimization of single near-infrared OPDs,which provides a basis for the next work.Second,we innovatively combined the transparent indium gallium zinc oxide(IGZO)thin film transistors(TFTs)with the near-infrared OPDs with PTB7-TH:FOIC as the active layer,and finally successfully prepared the simple process,high sensitivity near-infrared photodetector array.The transparent IGZO TFTs used in the experiment have good light transmittance,which is more conducive to the capture of light signals by the photodetector unit.In addition,IGZO TFTs also have excellent electrical properties,showing a high on-off ratio and low subthreshold swing.Based on near-infrared OPDs and transparent IGZO TFTs,the fabricated near-infrared photodetector array exhibits an ultra-low dark current density of 1.43×10^-8 A cm^-2,low noise current of 3.90×10^-13A Hz^-1/2 and a high D*of 4.01×10¹² Jones at 850 nm.Compared with single OPDs,the dark current and noise current of the device are one and two orders of magnitude lower,respectively,and D*is two orders of magnitude higher.Finally,the near-infrared photodetector array is applied to the near-infrared imaging system and PPG signal detection system,showing the application potential of the device.This thesis completes a series of work on near-infrared OPDs from material selection,device optimization,system integration,and finally to practical application,and conducts an in-depth analysis of them.The innovative combination of transparent IGZO TFTs and near-infrared OPDs containing FOIC provides a research idea for the simple process and high-performance near-infrared photodetector array.This work has a certain enlightening value and application value for the field of photodetectors.