Ultrafast Exciton Dissociation at the 2D-WS ₂ Monolayer/Perovskite Interface

For an excitonic photovoltaic (PV) device to perform efficiently, photogenerated excitons in the charge donor need to be dissociated through charge transfer (CT) to the acceptor rapidly after their photogeneration and remain separated for a longer time to allow the collection of charges. To improve the efficiency of these steps, several combinations of materials have been examined. Due to their excellent optical properties, two-dimensional transition-metal dichalcogenides (2D-TMDs) have recently been explored. Another promising class of materials to platform efficient PVs is organic-inorganic perovskites. Here, we report on the ultrafast exciton dissociation through electron transfer from a 2D tungsten disulfide (WS ₂ ) monolayer to a thin layer of methylammonium lead iodide (CH ₃ NH ₃ PbI ₃ ) perovskites. Photoluminescence measurements showed that when the 2D-WS ₂ monolayer was covered with perovskites, its emission completely quenched, suggesting that the CT process is highly efficient. Despite that pump-probe spectroscopy measurements were carried out with a ∼45 fs temporal resolution, the CT dynamics were not captured. A comparison of the ultrafast dynamics of the two band-edge excitons of the charge donor (2D-WS ₂ ) suggested that electron transfer is the dominant pathway of CT. Furthermore, these pump-probe measurements indicated that a small fraction of transferred electrons remained in the perovskites up to almost 2 ns. These findings may open a new horizon for understanding the dissociation of photogenerated excitons in 2D-TMDs through hybridization with another class of nanomaterials.