Room-Temperature Electrical Coupling of PbS Colloidal Quantum Dots for High-Performance N-Type Thin-Film...

Colloidal quantum dot (QD) films inherently exhibit a high Seebeck coefficient (α) and low thermal conductivity (κ), making them attractive for thermoelectric (TE) applications. However, achieving high electrical conductivity (σ) while preserving these advantages remains challenging due to limited interdot coupling and high-temperature treatments that compromise interdependent TE parameters. Herein, room-temperature inter-dot bridging of individual PbS QDs is demonstrated, leading to unprecedented electronic tunability and significant improvements in the n-type TE figure of merit (ZT). By tailoring the hydride concentration, gradual removal of surface ligands is induced, resulting in strengthened electrical coupling, structural ordering, and n-type doping of QD films. Consequently, σ is precisely modulated from ≈10^-6 to ≈10² S cm^-1, beyond the degeneracy transition regime where the maximum power factor (PF) is achieved. Importantly, a low κ of ≈0.25 W m^-1 K^-1 is preserved, elucidating the preferential charge transport enhancement without compromising phonon scattering. These effects collectively yield a substantially increased PF (103 µW m^-1 K^-2) and ZT = 0.14 at 330 K, which are among the highest reported for n-type TE thin-films processed under ambient conditions. This strategy provides a scalable, universal pathway for optimizing TE transport properties in QD-based devices, offering strong potential for flexible thermoelectric applications.