Transient structural evolution during electrochemical doping revealed by time‐aligned operando GIWAXS on organic mixed ionic electronic conductors

Organic mixed ionic–electronic conductors (OMIECs) exhibit dynamic structural transformations during electrochemical doping, critically impacting device performance in applications such as bioelectronics and neuromorphic computing. While operando grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) has emerged as a powerful tool to probe such changes, its temporal resolution remains fundamentally mismatched with the rapid ion dynamics in OMIECs, often obscuring transient microstructural states. Here, we introduce a time‐aligned operando GIWAXS methodology that bridges this gap by extending the electrochemical doping time constant through engineered device geometry. This enables real‐time tracking of structural evolution during abrupt doping conditions. Using poly(2‐(3,3′‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)‐[2,2′‐bithiophen]‐5‐yl)thieno[3,2‐b]thiophene) polymers with distinct molecular weights, we reveal that the microstructural response under abrupt biasing diverges significantly from that observed under conventional voltage‐sweeping conditions. Notably, abrupt doping induces intercalation pathways and reorientation behaviors not captured in quasi‐equilibrium measurements. Our approach provides direct insight into doping‐pathway‐dependent structural dynamics and offers a generalizable strategy for resolving rapid ion–polymer interactions in functional OMIEC systems. These findings highlight the importance of kinetic control in operando measurements and inform the rational design of mixed‐conducting polymer devices for transient or pulse‐driven applications.