Fabrication And Properties Of Solution-processed Field-effect Phototransistors

Photodetectors are a class of important electronic components that can convert optical signals into electrical signals.At present,there are various photodetectors covering the whole electromagnetic-wave spectrum.In daily life,photodetectors play an important role and are widely used in biomedical imaging,optical communication,remote sensing,environmental monitoring,autonomous driving,etc.Basic photodetector structures include photoconductors,photodiodes,and phototransistors.Among them,photodetectors prepared based on field-effect transistors exhibit the advantages of gate voltage regulation,high photoconductive gain,low noise,high detectivity,and easy integration compared with the other two-types of devices.Therefore,field-effect transistors exhibit great application prospects in the field of photodetection,and have attracted great attention of researchers.However,the semiconductor materials used as the channel layer often faces the situation that it is difficult to achieve both high mobility and high absorption at the same time,and the stability and flexibility of the device are both challenges in subsequent applications.To address these issues,researchers seek solutions from the perspective of materials and device structures.There are various types of channel materials to choose from,meanwhile,it is feasible to modify the material,improve the morphology,use composite films or explore new materials.On the other hand,considering the device structure,the use of layered structures or the formation of bulk heterojunctions,as well as the use of nanostructures in specific directions also showed great potential.This thesis will start with organic transistors and metal oxide transistors,and prepare high-performance field-effect transistor photodetectors from the perspectives of exploring new organic materials,using composite material channel layers,or using multi-layer structures:A novel organic semiconductor material D18 is used as the channel transport material,which exhibits high mobility and high absorption of visible light,and shows unipolarity,which can form a good P-type channel.The D18 field effect transistor is further optimized,which has an on-off ratio up to 10~6,low dark current and good repeatability and reproducibility.Based on this,a photodetector with low noise(about10 f A Hz^-1/2),high specific detectivity(4×10¹³ Jones)and excellent humidity,temperature and long-term stability was finally prepared.In addition,a flexible transistor photodetector based on D18 has also been prepared,which has achieved excellent optoelectronic properties and has been used for imaging.Based on the organic small molecule C8-BTBT with high mobility,composite films were formed with other semiconductors with good light absorption properties such as PC₇₁BM,IEICO-4F and AgBiS₂ quantum dots.To explore the performance of photodetectors based on composite thin films,field-effect phototransistors were fabricated.The study found that the photodetectors based on the composite film of C8-BTBT and AgBiS₂ quantum dots exhibited excellent optoelectronic properties,with decent photoresponse in the visible light spectral range,especially for ultraviolet light.Devices present specific detection rate of nearly 4×10¹³ Jones with 365 nm light irradiation.The ZTO field-effect transistors with high electron mobility is used as the substrate,additional antimony sulfide thin films with excellent optoelectronic properties and stability are used as the light absorption layer,and an electron transport layer is inserted between them.A photodetector with low noise(?11 f A Hz^-1/2),high specific detectivity(1×10¹³ Jones),and strong stability was obtained based on this structure.This work provides a feasible multilayer photodetector device structure,in which the insert layer and the light absorbing layer can be replaced by other semiconductors,showing great potential for photodetection.In this thesis,aiming at the preparation of high-performance field-effect phototransistors,the selection of channel layers and the design of device structure are systematically investigated,and the prepared photodetectors are fully characterized,which paves the avenue for the subsequent development and application of field-effect phototransistors.