To overcome the poor solubility of
the widely used p-type dopant
2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), we
have synthesized a series of structure-modified, organic p-type dopants
to include alkyl ester groups designed to enable solubility and miscibility
control. UV–vis–NIR and cyclic voltammetry measurements
show increased solubility of mono- and diester substituted dopants
with only modest changes to acceptor strength. Using absorption spectroscopy,
photoluminescence, and in-plane conductivity measurements, we demonstrate
that the new dopants can successfully p-type dope poly(3-hexylthiophene-2,5-diyl)
(P3HT). Monoester substituted dopants are characterized by only slightly
reduced electron affinity relative to F4TCNQ, but greater doping effectiveness
due to increased miscibility with P3HT. Diester substituted dopants
undergo a dimerization reaction before assuming their doped states,
which may help anchor dopants into position post deposition, thus
decreasing the negative effect of dopant drift and diffusion. We conclude
that increased dopant solubility/miscibility increases the overall
effectiveness of doping in solution-cast polymer films and that ester
modification is a practical approach to achieving solubility/miscibility
control in TCNQ-type dopants