Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Conjugated polymers are key materials for next-generation electronics, with electrical conductivity depending on charge carrier density and mobility.
• Carrier mobility in conjugated polymers is often limited by Coulombic traps formed by interactions between polarons and dopant counterions.
• Previous research demonstrated that large dodecaborane (DDB) dopants improve carrier mobility in ordered regioregular (RR) poly(3-hexylthiophene-2,5-diyl) (P3HT) by reducing polaron-counterion binding.

Purpose of the Study:

• To investigate the effect of large DDB dopants on polaron-counterion separation in chemically doped regiorandom (RRa) P3HT, a highly amorphous conjugated polymer.
• To assess the potential of DDB dopants to improve electrical conductivity in less-ordered conjugated polymer systems.

Main Methods:

• Chemical doping of RRa P3HT using DDB-based dopants.
• X-ray scattering analysis to determine polymer structure and ordering.
• Alternating Field (AC) Hall measurements to quantify carrier mobility.
• Electrical conductivity measurements of doped polymer films.

Main Results:

• DDB dopants induced partial ordering in amorphous RRa P3HT, forming a doped polymer crystal structure similar to that observed in DDB-doped RR P3HT.
• Alternating Field (AC) Hall measurements confirmed comparable hole mobility in DDB-doped RRa P3HT to that in DDB-doped RR P3HT.
• The use of large DDB dopants significantly reduced Coulombic binding in amorphous regions, achieving a high doping efficiency of 77% in RRa P3HT films.
• DDB-doped RRa P3HT films exhibited a conductivity of 4.92 S/cm, approximately 200 times higher than films doped with the traditional F4TCNQ dopant.

Conclusions:

• Tailoring dopants to promote mobile charge carriers in both amorphous and semicrystalline regions of conjugated polymers is an effective strategy for enhancing overall conductivity.
• The size and shape of dopants are crucial for achieving Coulombically unbound, mobile polarons, especially in less-ordered polymer materials.
• DDB dopants offer a promising route to significantly increase the conductivity of low-cost, randomly-regioregular conjugated polymers for electronic applications.