Giant Seebeck Effect of Dibenzo[g,p]chrysene and its Derivatives: Deuteration and Substituent Effects and Relationship with Interlayer Distance

Thermoelectric properties of undoped crystals of dibenzo[g,p]chrysene (DBC), deuterated DBC (DBC-d16), and 2,10-dimethyl-DBC (DBC-Me2) have been studied to obtain some insights into the relationship between the structural parameters of materials and the giant Seebeck effect. X-ray crystallography showed one-dimensional columnar packing with the interlayer distances (d) for DBC-d16, DBC, and DBC-Me2 were 3.78 Å, 3.79 Å, and 3.91 Å, respectively. All three compounds formed one-dimensional carrier transport pathways as suggested by the transfer integral calculations. Their Seebeck coefficients (α) were negative, indicating n-type behavior. DBC-d16 exhibited among the highest peak Seebeck coefficient (αmax = -114 mV/K) compared to DBC and DBC-Me2 (αmax = -31 and -22 mV/K, respectively). The power factors of DBC-d16 and DBC-Me2 were higher than that of DBC, due to an increase in Seebeck coefficient and conductivity, respectively. Notably, a positive correlation was found between the peak temperature of the Seebeck coefficient and interlayer distance d, while |αmax| correlated negatively with d. Deuteration significantly enhanced |αmax|, likely due to reduced molecular vibrations, though further investigation should consider the effect of dynamic structural fluctuation due to thermal motion.