The chemical and structural origin of efficient p-type doping in P3HT

► We study the p-type doping of P3HT with optical absorption and X-ray diffraction. ► F4TCNQ forms charged complexes with P3HT in solution above a certain concentration. ► We reveal a previously unreported crystalline phase in F4TCNQ doped P3HT films. ► Chemical state of P3HT in solution impacts thin film properties. ► Maximum film conductivity of 1.8 S/Cm is observed at ∼17% dopant concentration.