Nanoscale-surface roughness enhances the performance of organic thin-film thermoelectrics

Organic thermoelectric materials would be ideally suited for wearable thermoelectric devices but currently are not efficient enough for practical applications. Previous research efforts have tailored the composition, oxidation status, or doping levels of organic thin-film thermoelectrics to maximize their thermoelectric performance typically measured by the thermoelectric figure of merit (ZT). This study demonstrates that the thermoelectric ZT of the organic thin-films can be significantly boosted by increasing the surface roughness of the films. A simple soft-templating method that can produce nanorough thin films of organic thermoelectrics was developed and used to fabricate nanorough poly(3,4-ethylenedioxythiophene):Tosylate (PEDOT:Tos) thin films. The performance of the nanorough PEDOT:Tos films was compared to that of the smooth PEDOT:Tos films. The ZT value of the nanorough films was estimated to be 0.99, which is 83% higher than that of the smooth films and one of the highest ever reported for organic thermoelectrics. The flexibility and durability of the nanorough PEDOT:Tos films were also proved. A proof-of-concept thermoelectric device that used 5 strips of nanorough films, as the p-type thermoelectric elements, and five strips of bismuth thin films, as the n-type elements, produced 118.7 nW when ΔT = 50 K.