Organic/Inorganic Hybrid Infrared Photodetectors Based On Optical Capture Structure

Advanced infrared optical imaging system has a very broad application prospect in scientific research,imaging medicine,bionic sensing and military industry with the rapid development of economy and science and technology.A typical infrared optical imaging system consists of a lens and a photodetector array.Among them,for the core infrared photodetector array part,the broadband organic infrared photodetector has become a potential choice to replace the inorganic infrared photodetector because of its low cost,flexibility,wide operating temperature range and large-area manufacturing.However,organic photodetectors still have some problems.First of all,from the perspective of optics,in the process of device preparation,since the organic materials have a certain light transmittance and the film thickness is thin,the incident light will cause transmission loss after passing through the organic photoactive layer,so that the incident light absorption rate of the device is low.,thereby reducing device performance.Secondly,from the perspective of electricity,organic materials have problems such as low carrier mobility,slow response speed,and poor stability.In this paper,photoconductor-type and photodiode-type organic infrared photodetectors were prepared based on the organic conjugated polymer DPPT-TT,and improvements were made to the device structure or materials to address the above problems,such as using integrated mirror systems under the substrate,impurity doping and other methods to improve the device performance.Finally,the appropriate device is selected as the basic unit for the preparation of organic photodetector arrays.The specific work in this paper is as follows:（1）For the organic photoconductor,gold（Au）with an interdigitated pattern was deposited as an electrode on top of the organic film.After performance characterization of the device,its performance was poor.After analyzing the optical path of the device,the following conclusions are drawn:the organic film itself is thin（about tens of nanometers）and the substrate uses high-transparency glass.When the device is working,only a small part of the incident light is absorbed by the organic photoactive layer,and the rest is transmitted into the air medium through the organic layer,resulting in high transmission loss,thereby reducing the performance of the device.Therefore,in the improvement stage of the device,by adding a metal single-layer film mirror system under the substrate,the original transmitted light is reflected back to the organic photoactive layer through the mirror system for secondary absorption,and the absorptivity of the incident light is increased.Improve performance.Finally,we characterized the performance of the improved organic infrared photoconductor.Taking the incident light at 850 nm as an example,the responsivity of the organic infrared photoconductor with aluminum metal single-layer film mirror increased by 2079%,reaching0.039 A/W.（2）For organic photodiodes,an electron transport layer（ETL）and a hole transport layer（HTL）are added to the cathode and anode parts of the device,respectively,to reduce dark current and increase carrier mobility.On this basis,on the one hand,the electrode on the side of the incident light is changed to an open structure,which can make the incident light contact with the organic photoactive layer in a large area,thereby improving the light absorption;On the other hand,the device stability improves and the performance of the base device maximizes by adjusting the process parameters in the preparation process.In addition,organic thin films are also doped with a variety of materials,including polar complementary materials,thermoelectric materials,and other materials that enhance infrared light absorption in order to further improve device performance.Finally,the responsivity of the organic infrared photodiode doped with PC₇₁BM was increased by 5023.58%,reaching 4.581 A/W.At the same time,the specific detectivity and external quantum efficiency are also significantly improved.After shrinking the size and adding peripheral circuits and other processes,it can be used as the basic unit of the organic infrared photodetection array.