Dopant-Assisted Matrix Stabilization Enables Thermoelectric Performance Enhancement in n-Type Quantum Dot Films.

Abstract

Efficient thermoelectric generators require further progress in developing n-type semiconductors that combine low thermal conductivity with high electrical conductivity. By embedding colloidal quantum dots (CQDs) in a metal halide matrix (QDMH), the metal halide matrix can enhance phonon scattering, thus suppressing thermal transport; however, simultaneously achieving high electrical conductivity in such systems has previously been limited by the deleterious impact of a large density of interfaces on charge transport. Therefore, new strategies are needed to improve charge carrier transport without sacrificing matrix-enabled low thermal transport. Here, we report the use of chemical doping in the solution state to improve electron transport while maintaining low thermal transport in QDMH films. By incorporating cesium carbonate (Cs2CO3) salts as a dopant prior to matrix formation, we find that the dopant stabilizes the matrix in colloidal inks and enables efficient n-type doping in QDMH films. As a result, this strategy leads to an enhanced n-type thermoelectric behavior in solution-processed QDMH films near room temperature, with a thermal conductivity of 0.25 W m–1 K–1—significantly lower than in prior films based on organic-ligand-cross-linked CQD films (>0.6 W m–1 K–1) and spark-plasma-sintered CQD systems (>1 W m–1 K–1). This study provides a pathway to developing efficient n-type thermoelectric materials with low thermal conductivity using single-step deposition and low-temperature processing.