Work

Quantifying Doping Efficiency to Probe the Effects of Nanoscale Morphology and Solvent Swelling in Molecular Doping of Conjugated Polymers

Year: 2024

Type: article

Abstract: We study the doping of conjugated polymers from droplets of molecular dopant solutions, as might be used in additive manufacturing approaches. We compare the doping efficiency of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) solutions between two model conjugated polymers, regioregular poly(3-hexylthiophene) (P3HT) and poly(bithiophene-thienothiophene) copolymer with a triethylene glycol side chain (P(g 3 2T-TT)). We find that F4TCNQ dopes P(g 3 2T-TT) more efficiently from solution, producing films with >10 3 times higher conductivity. Using spectroelectrochemistry to calibrate polaron spectra to known hole injection levels, we quantify the doping efficiency (polarons created/dopant molecule added) to be higher than 170% for P(g 3 2T-TT) but only 47.2% for P3HT. We further explore the differences in molecular doping using a combination of scanning Kelvin probe microscopy (SKPM) and conductive atomic force microscopy (cAFM). We explore doping efficiency and aggregation as a function of the solvent of the dopant solution, side chain, and regioregularity of conjugated polymers; we show that the doping efficiency and dopant aggregation are both correlated with the ability of the dopant/solvent solution to swell the conjugated polymer, with combinations that swell, resulting in more efficient doping and smoother films with less aggregation.

Source: The Journal of Physical Chemistry C

DOI: 10.1021/acs.jpcc.4c00153