Solar energy harvesting offers sustainable, environment-friendly, and inexpensive methods for the production of electrical energy and chemical fuels. The efficiency of photovoltaic and photocatalytic materials depends on the energy and charge transfer dynamics, nonradiative recombination of photogenerated charge carriers, and the dynamics of cooling of hot holes and electrons in the band edges. We employ first principles nonadiabatic molecular dynamics (NA-MD) calculations to rationalize the excited state dynamics at the interface of novel heterostructured nanomaterials. Our NA-MD calculations suggest that van der Waals heterostructures formed from a 2D material such as silcane (SiH) or germanane (GeH), and a TiO2 surface form promising photocatalysts. How the chemistry of TiO2 surfaces (anatase vs rutile) and 2D layers (H vs Me functionalization) affect the photocatalytic properties of a heterostructure is investigated from the perspective of electronic structures, nonradiative recombination timescales, and hot carrier relaxation dynamics. In another study, we explore the excited state charge and energy relaxation dynamics at the monolayers of black-phosphorous (BP) and graphitic carbon nitride (g-C3N4), and at the interface of BP/g-C3N4 heterostructure. In good agreement with the previous experimental studies, we show ultrafast relaxation timescales for the photogenerated charge carriers in BP, whereas slow nonradiative recombination on the order of several nanoseconds was found for g-C3N4. The capping of BP with g-C3N4 furnishes both good photoabsorption efficiency and longer recombination timescales. We investigate the dynamics of phonon-induced cooling of hot charge carriers and characterize the vibrational modes involved in the dynamics. The factors that contribute to the carrier dynamics namely, excitation energy, nonadiabatic coupling between electronic states, and decoherence effects are estimated and explained based on simple geometric, electronic, and symmetry effects.

Excited state dynamics of charge carriers at the interfaces: Insights from nonadiabatic molecular dynamics calculations

255th National Meeting (2018)

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