Photoactivated Doping Enables Structural Ordering and Efficient Charge Transport for Organic Thermoelectrics

Molecular doping is an essential strategy for controlling charge carrier density in conjugated polymers (CPs) and improving organic thermoelectric (TE) performance. However, conventional mixed-solution doping often introduces structural disorder through solution-phase charge-transfer interactions, limiting charge transport despite increased carrier density. Although doping-induced ordering has emerged as a promising route to enhance both carrier density and mobility, it has mainly been observed in sequential doping systems. Here, we demonstrate a photoactivated doping approach that enables structural ordering in a mixed-solution process. A UV-responsive dopant, triphenylsulfonium hexafluoroantimonate (TPS-HA), suppresses charge transfer during solution processing and activates doping only after film formation. This temporal separation minimizes disruption of the polymer microstructure. Prior to activation, TPS-HA is primarily located in amorphous regions of poly(3-hexylthiophene) (P3HT), preserving the native crystalline framework. Upon UV irradiation, charge carriers are generated and SbF₆⁻ counterions are incorporated into lamellar regions, promoting side-chain ordering, backbone planarization, tighter π–π stacking, and reduced structural disorder. The resulting structural reorganization promotes carrier delocalization and improves charge transport. Photoactivated doping yields an electrical conductivity of 78 S cm⁻¹ and a power factor of 51 μW m⁻¹ K⁻². Charge transport analysis based on the Kang–Snyder model reveals a transport exponent of s = 1, indicating low structural disorder induced by photoactivated doping. Structural and spectroscopic analyses further confirm enhanced molecular ordering following photoactivation. These findings demonstrate that photoactivated doping can reconcile high doping levels with preserved molecular order in CPs, providing a scalable strategy for high-performance organic TE materials.