Low-Temperature-Processed Colloidal Quantum Dots as Building Blocks for Thermoelectrics

Colloidal quantum dots (CQDs) are demonstrated to be promising materials to realize high-performance thermoelectrics owing to their low thermal conductivity. The most studied CQD films, however, are using long ligands that require high processing and operation temperature (>400 °C) to achieve optimum thermoelectric performance. Here the thermoelectric properties of CQD films cross-linked using short ligands that allow strong inter-QD coupling are reported. Using the ligands, p-type thermoelectric solids are demonstrated with a high Seebeck coefficient and power factor of 400 μV K ⁻¹ and 30 µW m ⁻¹ K ⁻² , respectively, leading to maximum ZT of 0.02 at a lower measurement temperature (<400 K) and lower processing temperature (<300 °C). These ligands further reduce the annealing temperature to 175 °C, significantly increasing the Seebeck coefficient of the CQD films to 580 μV K ⁻¹ . This high Seebeck coefficient with a superior ZT near room temperature compared to previously reported high temperature-annealed CQD films is ascribed to the smaller grain size, which enables the retainment of quantum confinement and significantly increases the hole effective mass in the films. This study provides a pathway to approach quantum confinement for achieving a high Seebeck coefficient yet strong inter-QD coupling, which offers a step toward low-temperature-processed high-performance thermoelectric generators.