Control Aggregation of P3HT in Solution for High Efficiency Doping:Ensuring Structural Order and the Distribution of Dopants

Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the dopant crucially determine electrical conductivity of the doped polymer.However,in solution-mixed doping,the interplay between polymer and dopant leads to highly structural disorder of polymer and random arrangement of dopant.Here,we propose a strategy to ensure the dopant induced polarons have high charge dissociation and transport by letting the conjugated polymers aggregate in the marginal solvent solution by cooling it from higher temperature to room temperature.We select poly(3-hexylthiophene-2,5-diyl)(P3HT)solution doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)as a model system.P3HT crystallizes in the marginal solvent,such as 1,1,2-trichloroethane(TCE)driven by the favorπ-πinteraction between planar polymer backbone.The dopant F4TCNQ enters the alkyl side chain region not theπ-πstacking region and thus guarantees high crystallinity and theπ-πinteraction of P3HT.This distribution of F4TCNQ which away from the polymer backbone to ensure higher charge dissociation and transport.Finally,we obtained a high conductivity value of 23 S/cm by doping P3HT with 20%F4TCNQ by using the marginal solvent,which is higher than doping P3HT with a disordered coil conformation in chlorobenzene(CB)of 7 S/cm,which the dopants enter both the alkyl side chain region and theπ-πstacking region.