Multipolaron Complexes in Conducting Polymers: The Importance of Hole-Hole Repulsion in Charge Delocalization

Multipolaron complexes in p-doped poly(3-hexylthiophene) films are investigated theoretically for polaron-anion configurations in which stationary dopant anions are positioned on both sides of the polymer chain, within the lamellar region. Complexes as large as tetrapolarons, consisting of four anions and an equal number of mobile holes, are considered. It is found that the mid-IR absorption band (P1) red-shifts and the hole ionization potential decreases as the complex grows in size, from a single polaron to a tetrapolaron. Such behavior is shown to arise mainly from enhanced hole delocalization due to hole-hole repulsion and has important implications for charge transport in organic materials.