Ratio Effect Of Vinyl Linkers In A Series Of Conjugated Polymers For Carrier Mobility

Generally,conjugated polymers are a class of skeletons that are cross-connect by conjugated systems.The band gap become more narrow owing to the polymer has a large conjugated system,so that the conjugated polymer has unique photoelectric properties.So organic electronics,chemical and biological sensors and other fields have been practical application.The semiconductor material has the advantages of lower cost,better flexibility,smaller pollution and simpler preparation procedure,which characteristics that are not present on the inorganic semiconductor materials.Charge carrier mobility in conjugated polymers is determined by two aspects:the inter-chain and intra-chain charge transport.Lowering the crystallinity in a conjugated polymer implies weakening of the inter-chain interaction,which would reduce the inter-chain charge transport and consequently reduces the carrier mobility.Therefore,a low mobility in a weakly crystalline conjugated polymer is seemingly inevitable.However,the latest studies suggest that charge transport in semiconducting polymers pre-dominantly occurs along the backbone and requires only occasional intermolecular hopping through short p–p stacking bridges.Fusing multiple vinyl linkages into the backbone of a donor–acceptor conjugated polymer might be another possible solution to achieve such a task.Therefore,we introduce multiple vinyl linkages into backbone of conjugated polymers to investigate that influence on the crystallinity and mobility of conjugated polymers,and we can futher explore the relation among the ratio of vinyl linker,crystallinity and charge carrier mobility in a series of benzothiadiazole-quarter thiophene based conjugated polymers which could provide new thoughts in designing performance flexible transistor in future.The details as follow:（1）A conjugated polymer PTBTV based on benzothiadiazole and dithiophene with multi-vinyl linkages（the ratio of vinyl linkages is 100%）was synthesized.Electrochemical and optical studies indicate the LUMO and HOMO energies of the polymer are-3.70 eV and-5.39 eV which also show classical p-type property.Theorietical calculation with density functional theory revealed an enhanced planarity of the oligomer backbone for PTBTV which are considered beneficial for charge transport along the polymer backbone.Bottom contact bottom gate organic field effect transistor devices base on PTBTV were fabricated and examined in air.After annealing at 160 ^oC,the devices exhibit excellent performance ofμ_h=3.2 cm²V^-1s^-1,I_on/off=10⁶,V_T=-7V,_there were no further enhancements of the OFET‘s performance after annealing at higher temperatures.Thin film morphologies before and after the annealing process are also investigated with GIXRD and AFM.（2）Four polymers PB4TV0,PB4TV1,PB4TV2 and PB4TV3 containing 0 to 3vinyl linkers in the repeating unit are synthesized.Four polymers PB4TV0,PB4TV1,PB4TV2 and PB4TV3 containing 0 to 3 vinyl linkers in the repeating unit are synthesized Electrochemical and optical studies indicate that the none vinyl contained PB4TV0 exhibited HOMO of-5.65 eV,where as PB4TV1,PB4TV2 and PB4TV3showed HOMO of-5.50,-5.48 and-5.41 eV,respectively.This complied with the previous literature that introducing vinyl linkage would lead to a strengthened co-planarity of polymer backbone and extended conjugational length,thus a higher HOMO level is in order.Theorietical calculation with density functional theory revealed that dehedral angle of vinly linked oligomers is smaller than none-vinly oligomers,which correspond with our hypothesis that vinyl can improve the conjugational length and co-planarity of the polymer backbon.Bottom contact bottom gate organic field effect transistor devices base on PB4TV0,PB4TV1,PB4TV2 and PB4TV3 were fabricated and examined in air.Thin film morphologies before and after the annealing process are also investigated with GIXRD and AFM.