  Conjugated polymers are increasingly used as organic mixed ionic-electronic
conductors in electrochemical devices for neuromorphic computing,
bioelectronics and energy harvesting. The design of efficient applications
relies on high electrochemical doping levels, high electronic conductivity,
fast doping/dedoping kinetics and high ionic uptake. In this work, we establish
structure-property relations and demonstrate how these parameters can be
modulated by the co-existence of order and disorder. We use in-situ
time-resolved spectroelectrochemistry, resonant Raman and terahertz
conductivity measurements to investigate the electrochemical doping in the
different morphological domains of poly(3-hexylthiophene). Our main finding is
that bipolarons are found preferentially in disordered polymer regions, where
they are formed faster and are thermodynamically more favoured. On the other
hand, polarons show a preference for ordered domains, leading to drastically
different bipolaron/polaron ratios and doping/dedoping dynamics in the distinct
regions. We evidence a significant enhancement of the electronic conductivity
when bipolarons start being formed in the disordered regions, while the
presence of bipolarons in the ordered regions is detrimental for transport. Our
study provides significant advances in the understanding of the impact of
morphology on the electrochemical doping of conjugated polymers and the induced
increase in conductivity.
