Integration of Photoresponsive Single-Molecule Bithermoelectric Devices

Organic thermoelectric materials capable of converting heat into electricity become important for sustainable energy conversion. Single-molecule thermoelectric devices present a promising opportunity for high-efficiency thermopower conversion by precisely controlling molecular energy levels, which induces energy-dependent transport asymmetry and consequently enhances the Seebeck coefficient. However, scalable thermopower output remains constrained by the challenges of assembling heteromolecular thermoelectric units with opposite polarities, whereas dynamic in situ control over the polarity of the Seebeck coefficient offers a feasible strategy for overcoming this limitation. Here, we report a photoresponsive single-molecule bithermoelectric device based on dithienylethene (DTE) derivatives using the scanning tunneling microscope break-junction (STM-BJ) technique with a thermoelectric module. The Seebeck coefficient could be reversibly switched between positive (P-type) and negative (N-type) values upon respective UV and visible light irradiation, as confirmed by thermoelectric measurements and density functional theory (DFT) calculations. By assembling an array of DTE monolayer with an optical mask to partially trigger the photoisomerization, we experimentally realized alternating P-type and N-type DTE molecular junctions connected through interleaved top and bottom electrodes, yielding a series-integrated molecular thermoelectric device with an amplified thermopower output over 9000 μV under a temperature gradient of 30 K. This study presents a viable strategy for realizing programmable and scalable molecular thermoelectrics by utilizing photoswitchable bithermoelectric molecular devices.