Competition between Phonon-Assisted and Exciton Photoluminescence Modulated by Temperature in WSe2/Graphene Nanosheet Heterostructures for Flexible Optoelectronic Sensor Devices

Temperature field engineering provides a robust framework for investigating the behavior of phonons and excitons within two-dimensional (2D) layered van der Waals materials. Herein, we measured the photoluminescence (PL) spectroscopy of few-layer WSe2 and WSe2/graphene van der Waals heterostructures at various temperatures (from 10 to 300 K). The results indicate that the PL intensity of the heterostructure is lower than that of few-layer WSe2, which is attributed to charge transfer at the interface under photoexcitation conditions. The PL spectroscopy spectrum of the heterostructure is primarily composed of four distinct spectral features, arising from distinct phonon-assisted processes, direct recombination, and excitonic contributions. Furthermore, these physical processes can be modulated by varying the temperature. For instance, the phonon-assisted PL process gradually diminishes with the decrease in temperature, whereas the excitonic PL process emerges more distinctly with the reduction in temperature. These findings can provide support for understanding the photophysical processes in 2D heterostructure materials and lay the groundwork for optoelectronic devices based on nanomaterials.