Effects Of Chemical Modification And Solvent Processing On Mechanical Properties Of Conjugated Polymers

Compared with traditional inorganic semiconductor materials,organic polymer semiconductor materials have the greatest advantage of natural flexibility,but this natural flexibility is hard to meet the need as an active layer of flexible electronic devices.Although many modification strategies of polymers can greatly improve flexibility,these methods can not meet the requirements of high carrier mobility and good mechanical flexibility as active layers at the same time.Therefore,achieving good electrical properties and ductility of polymer semiconductors has always been a challenge task.In this paper,chemical modification and processing with different solvents are used to improve both mechanical and electrical properties.The details are as follows:?1?A series of isoindigo derivative-based conjugated polymers were studied in an effort to gain a better understanding of the influence of polymer main and side chain structures on their electrical and mechanical properties.The results show that the introduction of alkyl side chains onto the donors can significantly enhance the mechanical properties of isoindigo-based polymers,however,the electrical properties of the films greatly deteriorated due to the large steric hindrance by the chain.The insertion of strong electron-withdrawing units,such as benzodifurandione into isoindigo chain?PBIBDF-BT?,significantly boosted the electrical properties of the films without decreasing their mechanical properties.The crack onset in PBIBDF-BT thin films was observed at 50%tensile strain.In addition,PBIBDF-BT thin films exhibited bipolar transport properties with both electron and hole mobilities greater than0.1 cm² V^-11 s^-1 at 100%strain.It is found that the improvement of PBIBDF-BT performance is attributed to its proper molecular structure.The long alkyl side chains significantly increase the ductility of PBIBDF-BT thin films,and the strong electron-withdrawing BIBDF unit in the main chains enhances the local aggregation,resulting in a significant increase in mobility.These results indicate that the mechanical and electrical properties of conjugated polymers could simultaneously be improved through reasonable molecular design.?2?The effects of different solvents on the mechanical properties of conjugated polymers were studied.The difference between conjugated polymer films processing with chlorobenzene and chloroform as solvents on the microstructures were studied in detail,and then the effects of microstructures on the mechanical and electrical properties of polymer films were analyzed.The UV-vis-NIR absorption spectroscopy results show that the absorption peaks of P3HT films using chlorobenzene as solvent are stronger at 605 nm,which indicates that the interaction between conjugated molecular chains is stronger.This makes the ordering degree of polymers in the films higher,the stacking of crystalline regions more compact,and leading to the decrease of surface roughness.The smooth and compact surface morphology of the film makes the tensile strain dissipate more uniformly on the film surface,and the mechanical properties of the film are improved significantly.There are no cracks under 100%tensile strain.At the same time,the better crystallinity can greatly improve its mobility,and the maximum mobility can reach 0.035 cm² V^-1 s^-1.