ZnO/Organic superlattice with phase composite structure for enhanced thermoelectric performance at low temperature

• Introduced a novel approach to simultaneously enhance the power factor and reduce lattice thermal conductivity using a hybrid superlattice composed of ZnO and organic monolayers. • Engineered ZnO nanolayers to feature a unique amorphous-nanocrystalline phase-composite structure within the nanolayers. • The integration of phase-composite nanolayers into the superlattice structure led to a five-fold improvement in power factor and a two-fold decrease in thermal conductivity. • Achieved the highest ZT values among n-type metal oxide thermoelectric materials, setting a new standard in the field. Semiconducting metal oxides, such as zinc oxide (ZnO), are gaining recognition for thermoelectric applications due to their temperature stability, availability, eco-friendliness, and cost-effectiveness. However, ZnO faces challenges in achieving high ZT value due to its low carrier concentration and high thermal conductivity. Traditional methods, like doping and defect engineering, have shown limited success in overcoming these challenges. In this study, we introduce a unique superlattice structure with a phase-composite composition that significantly decreases thermal conductivity through enhanced phonon scattering while maintaining the power factor by inducing new resonant conducting states near the mobility edge. By optimizing nanolayer thickness and doping concentration, we achieved a remarkable power factor of 14.6 μW cm −1 K −2 and reduced thermal conductivity to ∼1.97 W m −1 K −1 at room temperature in samples with 6 nm-thick ZnO nanolayers fabricated at 100 °C. This leads to a ZT value of ∼0.22 at 300 K, the highest among metal oxide thermoelectric materials at low temperatures, which further increases to ∼0.55 at 510 K. These findings demonstrate the potential of hybrid superlattices for efficient low-temperature thermoelectric applications.