Van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unprecedented opportunites for novel gate-tunable optoelectronic devices. Mixed dimension p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS2 (2D), are especially interesting for photovoltaic applications where absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library for 2D, organic, and inorganic photovoltaic materials. Here, for the first time, we study the kinetics of excited carriers in pentacene-MoS2 p-n type-II heterojunction by transient absorption sepctroscopy. We observe the dissociation of MoS2 excitons by a hole transfer to pentacene on the time scale of 6.7 ps, and a long-lived (5.1 ns) charge-separated state that is 2 to 60 times the recombination lifetime in previously reported n-n+ 2D heterojunctions . By studying fractional amplitudes of the MoS2 decay processes we determine a 50% hole transfer yield from MoS2 to pentacene, where the remaining holes undergo ultrafast trapping due to surface defects. The ultrafast charge transfer and long-lived charge-separated state in this pentacene-MoS2 Van der Waals heterojunction fulfills the requirements for high-performance photovoltaics using mixed dimensional van der Waals nanomaterials, and provide a platform for the development of future devices.
|Original language||English (US)|
|State||Published - Mar 7 2017|
- Transient absorption spectroscopy
- Transition metal dichalcogenides
- Van der Waals heterojunctions
ASJC Scopus subject areas