Introducing Solubility Control for Improved Organic P-Type Dopants

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.