Spontaneous Doping at the Polymer-Polymer Interface for High-Performance Organic Transistors.

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Chemistry

Background:

• Low-k amorphous fluorinated polymers, such as poly(perfluoroalkenylvinyl ether) (CYTOP), are utilized as gate dielectrics in organic field-effect transistors (OFETs).
• Their hydrophobicity and solvent orthogonality are crucial for device stability and compatibility with organic semiconductors.

Purpose of the Study:

• To investigate a novel functionality of fluorinated low-k polymer dielectrics in OFETs.
• To understand the mechanism behind the modulation of charge transport characteristics.

Main Methods:

• Fabrication of OFETs using indacenodithiophene-co-benzothiadiazole and diketopyrrolopyrrole-thieno[3,2-b]thiophene semiconductors.
• Comparison of device performance with conventional dielectrics (e.g., poly(methyl methacrylate)) versus fluorinated dielectrics (CYTOP, Teflon).
• Analysis of charge transport modulation through thermal annealing and investigation of interface dipole formation.

Main Results:

• Fluorinated dielectrics (CYTOP, Teflon) induced spontaneous p-doping at the dielectric-semiconductor interface.
• Ambipolar charge transport in OFETs was converted to unipolar p-type by using these fluorinated dielectrics.
• Thermal annealing led to C-F bond rearrangement and aligned dipole moments, causing a Fermi level downshift and p-doping effect.

Conclusions:

• Fluorinated low-k polymers possess a new functionality: spontaneous p-doping at the dielectric-semiconductor interface.
• This phenomenon enables the conversion of ambipolar charge transport to unipolar p-type in OFETs.
• The findings offer new avenues for designing organic electronic devices with tailored charge transport properties.