Ultrafast Carrier and Lattice Cooling in Ti2CTx MXene Thin Films

Abstract

Metallic MXenes are promising two-dimensional materials for energy storage, (opto)electronics, and photonics due to their high electrical conductivity and strong light-matter interaction. Energy dissipation in MXenes is fundamental for photovoltaic and photothermal applications. Here we apply ultrafast laser spectroscopy across a broad time range (femto- to microseconds) to study the cooling dynamics of electrons and lattice in emerging Ti2CTx thin films compared to widely studied Ti3C2Tx thin films. The carrier cooling time in Ti2CTx is persistently ∼2.6 ps without a hot-phonon bottleneck. After hot carrier cooling is completed, the transient absorption spectra of Ti2CTx MXene can be described well by the thermochromic effect. Heat dissipation in MXene thin films occurs over hundreds of nanoseconds with thermal diffusivities ∼0.06 mm2 s-1 for Ti2CTx and ∼0.02 mm2 s-1 for Ti3C2Tx, likely due to inefficient interflake heat transfer. Our results unravel the energy dissipation dynamics in Ti2CTx films, showcasing potential applications in energy conversion.