Investigation of simultaneous carrier/phonon scattering and bipolar conduction effects in inorganic/organic composites: Implications for thermoelectric performance

For low-temperature thermoelectric applications, a bulk-phase inorganic/organic composite is prepared by introducing a conducting polymer, which is recognized as a potential organic thermoelectric material, into a representative inorganic thermoelectric material (n-type BiTe). A conducting polymer, PEDOT:PSS, was chosen to prepare the BiTe/PEDOT:PSS composite, wherein an intimate interface was formed between BiTe and PEDOT:PSS. The work function difference between BiTe and PEDOT:PSS created an energy barrier at the interface, possibly facilitating selective charge carrier transport depending on the energy levels of the carrier (i.e., energy filtering effect), thereby contributing to an enhancement in the Seebeck coefficient. The composite exhibited a completely different bipolar conduction tendency from pristine BiTe, inducing a significant variation in the temperature dependence of the Seebeck coefficient. Furthermore, the interface may affect the carrier and phonon scattering probabilities, resulting in a considerable reduction in thermal conductivity. The composite adjustment was intensively studied to regulate the electrical and thermal properties using the energy filtering effect along with the carrier and phonon scattering probabilities, resulting in a noticeably enhanced thermoelectric performance. The temperature dependence of the performance was effectively adjusted using the bipolar conduction tendency, thereby affording the BiTe/PEDOT:PSS composite exhibiting consistently high ZT values over the wide temperature range of 25-275 °C. The thermoelectric performance of BiTe/PEDOT:PSS was competitive with that of previously reported high-performance n-type BiTe-based analogs. The BiTe/PEDOT:PSS composite is a promising n-type candidate for diverse low-temperature thermoelectric applications as a p-type BiTe counterpart.