OR1 : Molecular modelisation for flexible electronics

The electronic-ionic mixed transport properties associated with flexibility, extensibility and conformability are essential characteristics of organic semiconductors to built lightweight and less bulky technological devices and to develop portable or implantable human-machine interfaces in the field. organic bioelectronics.

The water-formulatable conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) associated with its counterion, the polyelectrolyte polystyrene sulfonate (PSS) constitutes the organic semiconductor “par excellence “for these various devices. However, so far, PEDOT:PSS films formed in the liquid phase exhibit much lower electrical conductivity than their inorganic counterpart (indium tin oxide).

In collaboration with the group led by Prof. Yun Hee Jang at DGIST in South Korea, we performed a multi-scale modeling (density functional and classical molecular dynamics) that provided the first molecular explanation and the first guideline to control the morphology of PEDOT:PSS by addition of ionic liquids. We have demonstrated an ion exchange between PEDOT+:PSS– and the ionic liquid A+:X– leading to the formation of large conductive domains in which PEDOT+ are stacked under the effect of π-π interactions and "decorated" by the anions. X–. The most efficient X– anions (TCB, TCM, HCCP) are large molecular size, hydrophobic and exhibit charge delocalization. They remain embedded in the PEDOT domains after the exchange and participate in the uniform distribution of charge carriers along the PEDOT backbone, thus inducing a further enhancement of conductivity.

Figure : Free energy of exchange showing the efficiency of X=TCM, TCB and HCCP anions, current-voltage curve
for different ionic liquids and formation of PEDOT domains under the action of TCB anion (the cation is EMIM).