A method for forming a conjugated polymer which is doped by a dopant includes the steps of (a) adding a doping agent comprising a dopant moiety to a solution containing the conjugated polymer or a precursor thereof and, optionally, a second polymer, the dopant moiety being capable of bonding to the conjugated polymer, precursor thereof or the second polymer; (b) allowing the dopant moiety to bond to the conjugated polymer, precursor thereof or the second polymer to perform doping of the conjugated polymer, wherein the amount of doping agent added in step (a) is less than the amount required to form a fully doped conjugated polymer.