Hot carrier localization in continuum states of a quantum dot solid

Abstract

Controlling hot-carrier relaxation in quantum-confined semiconductors remains a fundamental challenge in nonequilibrium condensed-matter physics. Here, we report for the first time that assembling colloidal quantum dots into a quantum dot solid (QDSolid) dramatically suppresses hot-carrier cooling by inducing transient localization in high-lying continuum states. Ultrafast transient-absorption spectroscopy reveals that carriers injected ∼1.2eV above the band edge in QDSolid remain localized for at least an order of magnitude longer than in uncoupled quantum dots. This localized population produces correlated high-energy photobleach and broadband photoinduced absorption features, observed universally across QDSolids of different sizes and compositions. First-principles density functional theory calculations attribute this phenomenon to the intrinsic positional disorder in the QDSolid, which generates local potential fluctuations that trap hot carriers. Our results demonstrate that positional disorder, often considered a limitation, can be harnessed to engineer localized carrier populations in extended quantum systems.