Study On Molecular Packing Behaviors And Optoelectronic Device Performances Of High Hole Mobility Conjugated Polymers

High mobility conjugated polymers have experienced considerable development,and have attracted extensive attention in the field of optoelectronic devices,such as the field effect transistors?OFETs?,organic photovoltaic cells?OPVs?and organic photodetectors?OPD_S?.The high mobility conjugated polymer has good solubility to meet low-cost solution processing technology,and has the application potential of fabricating large-area,flexible-substrate and portable electronic devices.Different from traditional inorganic semiconductor materials,conjugated polymers,as a new generation of semiconductor materials,have outstanding application compatibility,which can fully make up for the shortage of inorganic semiconductor materials in different application scenarios.The diversity of organic structures in polymer semiconductors enriches the design ideas of materials,but some materials have the problems of complex synthesis steps,difficult purification and low yield of finished products,which increase the research cost,time and energy consumption.On the other hand,starting from solid-state physics,making full use of the inherent characteristics of existing materials can greatly shorten the research and development cycle and cost of high-performance devices.Based on this,this thesis will focus on the research of the representative high hole mobility conjugated polymers,combining the relationship among the material properties of conjugated polymers,the processing technology of organic electronic devices and the device performance,and put forward the feasible strategies to optimize the device performance.In the 2nd chapter,a series of film samples of conjugated polymer FBT-Th₄?1,4?with high hole mobility were fabricated,and the effects of processing solvent,device substrate,polymer molecular weight,film thickness and fullerene derivatives on the molecular stacking behavior of the polymer were systematically analyzed in combination with the grazing in X-ray diffraction?GIXD?measurement.In terms of processing solvent,the effect is most prominent.The molecular orientation of the polymer film processed with chlorobenzene?CB?is edge-on,while the samples prepared with mixed solvent?CB:o-DCB?or o-dichlorobenzene?o-DCB?show a bimodal orientation of coexistence of face-on and edge-on.With the increase of o-dichlorobenzene content in the solvent,the orientation degree and grain size of the polymer increased obviously.In terms of device substrates,the polymer films based on PEDOT:PSS and OTS substrates show similar solvent dependence,while the solvent dependence of bilayer Zn O/PFN-Br substrate is not obvious.In the aspect of thickness of polymer film,the edge-on orientation of the sample with 60 nm thick film is significantly higher than that of the sample with 300 nm thick film,which shows that edge-on orientation is more easily distributed near the substrate side.When the polymer was blended with fullerene derivatives,the polymer obtained a certain amount of face-on orientation under the induction of fullerene molecules.Different from the above four points,the influence of molecular weight on the molecular stacking behavior of polymers is relatively small.In addition,from the GIXD results of 12polymer films,it can be observed that the changing of coherent length of?100?diffraction peaks can well describe the molecular stacking behavior of the polymer.It has been proved that the molecular stacking behavior of polymer FBT-Th₄?1,4?can be finely tuned by processing solvent in the previous chapter.In the 3rd chapter,we continued to choose the conjugated polymer to fabricate the field-effect transistors,SCLC hole-only devices,and polymer photovoltaic cells,respectively,and explored the influence of different processing solvents on the carrier transport property and photoelectric conversion performance of the polymer devices.The hole mobility of OFETs processed with chlorobenzene is 0.24 cm²V^-1s^-1.The hole mobilities of OFETs prepared with mixed solvent and o-dichlorobenzene processing can be significantly increased,which are 0.79 cm²V^-1s^-1 and 1.35 cm²V^-1s^-1,respectively.For the SCLC hole-only device,the processing solvent was changed from chlorobenzene to o-dichlorobenzene,and the hole mobility of the device gained an order of magnitude.For polymer:fullerene photovoltaic cells,the energy conversion efficiency of the devices prepared by mixed solvent processing is more than 10%,and the short-circuit current density is beyond 20 m A cm^-2.The fill factor of the o-dichlorobenzene processed device can be over 70%.Benefiting from this solvent tunable property,the polymer obtained bimodal molecular orientation of coexistence of edge-on and face-on,which optimized the carrier transport ability,promoted the formation of 3D charge transfer network,and achieved the better device performances.In the 4th chapter,a bulk heterojunction blend film,which is composed of a high hole mobility conjugated polymer Si25 and a narrow bandgap nonfullerene acceptor molecule IEICO-4F,is used as the active layer of the device.The bulk heterojunction has a good power conversion efficiency in inverted solar cells,while a lower dark current density and a broad spectral response range in conventional photodetector.The dark current density of the devices can be further suppressed by using the thick active layer strategy.The detectivity of the device in the near-infrared wavelength of 790 nm?950 nm exceeds 1×10¹³ Jones.In the high frequency region,the values of detectivity calculated by the dark current and the noise current,respectively,are very close.The 940 nm near-infrared light-emitting diode is used as the detection light source to characterize the conventional Si25:IEICO-4F photodetector with 350 nm thick active layer.The linear dynamic range of the photodetector can reach 130 d B,the cut-off frequency is more than 300k Hz,and the response time is less than 2.4s.Based on the bulk heterojunction Si25:IEICO-4F,with reasonable device structure and optimization strategy in mind,the detection performance of the device is greatly improved,and it is expected to get a further application in the near-infrared light detection field.