We report the increase in the mobility of charge carriers in regioregular poly 3-hexyl thiophene (RR-P3HT) films by mixing them with tetracyanoethylene (TCNE), which is examined by in situ time-resolved microwave conductivity (TRMC) and transient optical spectroscopy (TOS). TCNE acts not only as an electron acceptor which increases the number of charge carriers on photoexposure but also as a functional additive which enhances the mobility of the charge carriers. This conclusion was deduced from the results of fluorescence quenching, transient optical absorption and photobleaching, and comparison of the TRMC signal with the TOS signal. The combination of the TRMC and TOS techniques represents a comprehensive and fully experimental approach to the determination of the intrinsic carrier mobility in conjugated polymers.