Fabrication And Properties Of Fiber-based Organic Photodetectors

Fiber electronic devices have flexibility,lightweight,and weaving characteristics and have increasingly become an essential carrier of wearable devices.Fiber-based photodetectors have broad application prospects in health monitoring,biomedicine,and aerospace fields.Currently,the photoactive layers of fiber-based photodetectors are mostly made of inorganic semiconductors and their composite materials,which have the characteristics of high carrier mobility,high stability,and low exciton binding energy.However,its mechanical flexibility is poor,and its application in flexible electronics is limited.Organic semiconductor materials have intrinsic flexibility,high spectral absorptivity,and adjustable spectral response range and are more suitable for fiber-based photodetectors.A typical fiber-based organic photodetector is a diode type consisting of inner and outer electrodes,an electron/hole transport layer,and an organic photoactive layer.The commonly used technique for preparing multilayer heterogeneous films on fiber substrates is the solution-processed,which faces problems such as the design of orthogonal solvent systems and the optimization of the preparation process of functional layers.This thesis uses zinc wire and organic heterojunction photoactive materials to prepare fiber-based organic photodetectors,including two structures of wound type and coaxial type.And systematic research on its structure and performance,the research content is as follows:Based on the winding structure,the ZnO electron transport layer,PBDB-T:ITIC-Th organic photoactive layer,and PEDOT:PSS hole transport layer were sequentially prepared on the surface of zinc wire by dip-coating process.Two devices were prepared by winding silver wire and carbon nanotube fiber as external electrodes.The preparation method of the winding device is simple,and the external electrode does not involve solution processing,which simplifies the orthogonal solvent system of the multilayer thin film.The device has good rectification characteristics and can effectively suppress dark current under reverse bias.The carbon nanotube fiber electrode can maintain a soft and tight contact with the inner functional layer,which is conducive to charge collection and transmission.The responsivity is as high as 37 mA/W（740 nm）at-0.5 V bias,and the D^*is higher than 1×10¹¹ Jones.Based on the coaxial structure,the ZnO electron transport layer,PBDB-T:ITIC-Th organic photoactive layer,MoO₃ hole transport layer,PEDOT:PSS outer transparent electrode were sequentially prepared on the surface of zinc wire.Compared with the wound electrode,the fully-wrapped transparent electrode has a larger contact surface with the internal functional layer,improving photoelectric conversion efficiency.Firstly,the MoO₃ layer was prepared by an evaporation method.Experiments show that when the total film thickness of evaporation is 80 nm,the device has the best photoelectric response,and the rectification characteristics are apparent.The dark current can be effectively suppressed under reverse bias.The responsivity can reach up to 86.4 mA/W（760 nm）,D^*is higher than 1×10¹¹ Jones in the visible light band.In addition,the photoresponse of the device remains stable after continuous bending.Secondly,the MoO₃ layer was prepared by a solution method to realize the preparation of fiber-based organic photodetectors by an all-solution process.The MoO₃ prepared by solution processed shows considerable photoelectric performance as the evaporation process.Under the bias voltage of-0.5 V,the maximum responsivity is 80.68 mA/W（740 nm）,and the D^*is more excellent than1×10¹¹ Jones.The research in this thesis is expected to provide new ideas for preparing fiber-based photodetectors and promote the development of flexible and wearable electronics.