Phonon-Mediated Interlayer Charge Separation and Recombination in a MoSe2/WSe2 Heterostructure

• DOI: 10.1021/acs.nanolett.0c04955
• Publication Date: 2021-03-10T08:03:30Z
• Authors: Zilong Wang; Patrick Altmann; Christoph Gadermaier; Yating Yang; Wei Li; Lavinia Ghirardini; Chiara Trovatello; Marco Finazzi; Lamberto Duò; Michele Celebrano; Run Long; Deji Akinwande; Oleg V. Prezhdo; Giulio Cerullo; Stefano Dal Conte
• Keywords: Science Policy; WSe; Immunology; Biophysics; Marine Biology; layer breathing motions; charge separation; 02 engineering and technology; MoSe; dissociation; higher-frequency out-of-plane vibra.; Phonon-Mediated Interlayer Charge S.; 2D Heterostructure; interlayer charge transfer; TDDFT; femtosecond pump-probe spectroscopy; transition metal dichalcogenides; charge transfer; Cell Biology; heterostructure; recombination; Ab initio quantum dynamics simulations; Medicine; indirect-to-direct bandgap modulation; 0210 nano-technology; Physical Sciences not elsewhere classified; Biological Sciences not elsewhere classified

Monolayer transition metal dichalcogenides bear great potential for photodetection and light harvesting due to high absorption coefficients. However, these applications require dissociation of strongly bound photogenerated excitons. The dissociation can be achieved by vertically stacking different monolayers to realize band alignment that favors interlayer charge transfer. In such heterostructures, the reported recombination times vary strongly, and the charge separation and recombination mechanisms remain elusive. We use two color pump-probe microscopy to demonstrate that the charge separation in a MoSe2/WSe2 heterostructure is ultrafast (∼200 fs) and virtually temperature independent, whereas the recombination accelerates strongly with temperature. Ab initio quantum dynamics simulations rationalize the experiments, indicating that the charge separation is temperature-independent because it is barrierless, involves dense acceptor states, and is promoted by higher-frequency out-of-plane vibrations. The strong temperature dependence of the recombination, on the other hand, arises from a transient indirect-to-direct bandgap modulation by low-frequency shear and layer breathing motions.