Functionally Graded Semiconducting Polymer Thin Films as Organic Thermoelectrics

Molecularly doped semiconducting polymers have demonstrated great potential in organic thermoelectrics (TEs) for thermal energy management. Along with the efforts to increase material’s figure of merit, the use of functionally graded materials (FGMs) where TE properties are spatially controlled opens pathway to further improve TE device performance. However, experimentally fabricating FGMs has been a challenging task. In our study, we utilize the facile processability to modulate electronic properties through molecular doping of conjugated polymers to fabricate and characterize thin film of organic FGMs with gradient in dopant composition. Our work focuses on understanding the structural and TE properties (Seebeck coefficient and electronic conductivity) across the FG polymer films. Using 1D thermoelectric coupling model, we also predict the thermoelectric cooling performances based on our experimental transport properties. Cooling temperature, ΔT, and coefficient of performance are calculated through linear constitutive relations coupled with conservation of charge and energy. The results demonstrate that ΔT of graded samples are significantly improved compared to that of uniform profile. This study provides guidelines to further development on more complex FGMs.