Fabrication Of Phototransistor Based On Organic Semiconductor Thin Film

Organic phototransistors(OPTs)show great potential in practical applications,due to many attractive features,including solution processible,high flexibility,large-area manufacturing,and relatively low manufacturing cost.How to improve the performance of OPTs is of great research value.The most important physical processes of OPTs include the generation of photogenerated carriers and the transmission of carriers.How to effectively regulate charge transport and exciton recombination are the key issues in the study of high-performance devices.In recent decades,photo-induced intramolecular charge transfer(ICT)has attracted great attentions.Perylene diimide(PDI)derivatives have a large conjugated framework and excellent absorption capacity in the visible light region.They are easy to form a thin film structure with good?-?stacking,therefore exhibit good electronic transmission ability and have become the active material of many OPTsoelectronic devices,including organic field effect transistors(OFETs),sensors,biological imaging ect.This thesis applies photo-induced ICT effect in the design of new PDI derivatives and applied them in fabrication of organic photodetectors.The main purpose is to realize a balanced regulation of charge transport and exciton recombination.In addition,space-confined strategy is recently developed as an effective method for preparing thin films on the water surface.Through film transfer,organic laminated devices without solvent damage can be obtained.This method shows many advantages in the preparation of flexible devices with layered heterojunctions.In this thesis,space-confined strategy was studied and was used in fabrication photoelectric devices.The main content of this thesis includes the following five parts:Chapter 1 introduces the basic parameters of OPTs and the theoretical basis of photo-induced ICT and summarizes the development status of phototransistors and polymer film forming methods based on organic materials in recent years.Furthermore,the motivation and research strategy of this thesis is introduced.Chapter 2 reports the design,synthesize and characterization of two PDI derivatives,BNM-PTCDI and BPM-PTCDI.OPTss based on these molecules were prepared,and their OPTsical and electrical properties were characterized.The test results showed that the electron mobility of both molecules increase with the increase of the substrate temperature during the evaporation process.The maximum electron mobility reached 0.029 cm~2v^-1s^-1 and 0.045 cm~2v^-1s^-1,respectively.The phototransistors prepared with BNM-PTCDI as the active material showed excellent photoelectric response performance,with the photoresponsivity(R)reaches 1.20×10~3A/W,the detectivity(D*)reaches 3.38×10¹¹ Jones,and the detection limit is as low as 0.8?W·cm^-2.In contrast,the phototransistor based on BPM-PTCDI only shows a R of 8.1A/W and a D*of 1.41×10~9 Jones under the light intensity of 80?W·cm^-2.The significantly higher photoresponsivity of BNM-PTCDI is due to the photo-induced ICT.Theoretical calculation indicates that the HOMO energy level of BNM-PTCDI molecules is at-5.70 e V,which is mainly distributed on the naphthyl side groups.When the PDI skeleton is excited by light to form excitons,electron transfer from naphthyl groups to the PDI skeleton can easily take place.Chapter 3 reports the design,synthesize and characterization of two PDI tertiary amine derivatives,PQ-PDI and PD-PDI.The OPTsical properties,thermal stability and the photoelectric properties of the molecules were characterized.The test results show that PQ-PDI can be used in photodetection for 450 nm laser.With the lengthening of the illumination time,both materials show enhanced electrical conductivity,suggesting a long-term memory effect,which are potentially useful in synaptic devices.Chapter 4 prepares 2D C₈-BTBT single crystals and polymer PFT-100 films by space-confined strategy.The maximum hole mobility of C₈-BTBT 2D single crystal is0.13 cm~2v^-1s^-1.The mobility of the PFT-100 film is 0.030 cm~2v^-1s^-1,which is increased by 0.005 cm~2v^-1s^-1 compared with the spin coating method.The maximum R and D*of the OPTs based on the PFT-100 film are 26.4 A/W and 5×10¹⁰ Jones,respectively,when a laser with a light intensity of 0.25?W cm^-2(450 nm)is placed above it.This study provides a reference for the preparation of organic polymer films.Chapter 5 summarizes the research results of this thesis and discusses future research directions.