Ultrafast Singlet Energy Transfer before Fission in a Tetracene/WSe2 Type II Hybrid Heterostructure

Hybrid heterostructures comprising organic and two-dimensional (2D) layered semiconductors hold great promise for light harvesting and optoelectronic applications. Among them, organic materials that exhibit singlet fission (SF) in which one singlet exciton generates two triplet excitons are particularly attractive and can potentially improve the performance of the device. However, SFenhanced devices require that SF can compete with direct energy/charge transfer from the singlet exciton. Here, we performed ultrafast spectroscopic studies on a prototypical heterostructure consisting of tetracene (Tc) and monolayer WSe2. We show a type II band alignment with 16.5 ps hole transfer from photoexcited WSe2 to tetracene and a long-lived (similar to 565 ps) charge separation. Importantly, we show ultrafast (similar to 3.4 ps) singlet exciton energy transfer from photoexcited tetracene to WSe2, prior to the slow SF process (>20 ps) in tetracene. This study raises the challenge and calls for the careful design of SF-enhanced 2D optoelectronic devices.

Automated summary

Hybrid heterostructures combining organic and 2D layered semiconductors show great potential for light harvesting and optoelectronic applications. Particularly, organic materials displaying singlet fission (SF) are appealing due to their ability to generate two triplet excitons from one singlet exciton. However, successful SF-enhanced devices require careful design to ensure efficient singlet exciton transfer and competition with direct energy/charge transfer.