Achieving Phonon‐Glass Electron‐Crystal Behavior in Fully Organic Flexible Thermoelectrics

ABSTRACT Realizing phonon‐glass electron‐crystal (PGEC) behavior, which combines metal‐like charge transport with glass‐like thermal conduction, is a key strategy for advancing thermoelectric efficiency. Although this paradigm has been implemented in inorganic materials, its translation into organic systems, which are attractive for flexible and wearable devices, remains unexplored. Here, a fully organic route to PGEC behavior is achieved by incorporating polyvinyl alcohol (PVA) into a conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) matrix. The optimized composite exhibits semi‐metallic electronic transport and ultralow thermal conductivity close to its theoretical minimum. Hence, a substantially improved power factor of 74.5 µW m −1 K −2 and a maximum figure of merit of 0.10 are attained at 300 K, which are among the highest values reported for practical micrometer‐thick PEDOT:PSS films. The performance originates from hierarchical structural evolution in which PEDOT domains preserve delocalized conduction, while PVA nano‐crystalline phases and interfacial acoustic mismatch selectively scatter phonons. In contrast to inorganic fillers, the all‐organic composite maintains excellent flexibility, retaining more than 99.5% of its initial electrical conductivity after 20 000 bending cycles at a radius of 4.3 mm. These findings establish design principles for organic thermoelectrics and highlight their potential in high‐performance, self‐powered wearable devices.