Konkurrenz für Graphen (engl.)

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Graphen wird allgemein als Wundermaterial der Zukunft bezeichnet. Jetzt könnte es durch den ebenso zweidimensionalen Halbleiter MX2 Konkurrenz bekommen.

A new argument has just been added to the growing case for graphene being bumped off its pedestal as the next big thing in the high-tech world by the two-dimensional semiconductors known as MX2 materials. An international collaboration of researchers has reported the first experimental observation of ultrafast charge transfer in photo-excited MX2 materials. The recorded charge transfer time clocked in at under 50 femtoseconds, comparable to the fastest times recorded for organic photovoltaics.

The researchers have demonstrated for the first time, efficient charge transfer in MX2 heterostructures through combined photoluminescence mapping and transient absorption measurements. Having quantitatively determined charge transfer time to be less than 50 femtoseconds, the study suggests that MX2 heterostructures, with their remarkable electrical and optical properties and the rapid development of large-area synthesis, hold great promise for future photonic and optoelectronic applications.

Photoluminescence mapping of a MoS2/WS2 heterostructure with the color scale representing photoluminescence intensity shows strong quenching of the MoS2 photoluminescence.
Photoluminescence mapping of a MoS2/WS2 heterostructure with the color scale representing photoluminescence intensity shows strong quenching of the MoS2 photoluminescence.

Combining different MX2 layers together allows one to control their physical properties. For example, the combination of MoS2 and WS2 forms a type-II semiconductor that enables fast charge separation. The separation of photoexcited electrons and holes is essential for driving an electrical current in a photodetector or solar cell.

In demonstrating the ultrafast charge separation capabilities of atomically thin samples of MoS2/WS2 heterostructures, the researchers have opened up potentially rich new avenues, not only for photonics and optoelectronics, but also for photovoltaics.

MX2 semiconductors have extremely strong optical absorption properties and compared with organic photovoltaic materials, have a crystalline structure and better electrical transport properties. Factor in a femtosecond charge transfer rate and MX2 semiconductors provide an ideal way to spatially separate electrons and holes for electrical collection and utilization.

The researchers are studying the microscopic origins of  charge transfer in MX2 heterostructures and the variation in charge transfer rates between different MX2 materials.

They are also interested in controlling the charge transfer process with external electrical fields as a means of utilizing MX2 heterostructures in photovoltaic devices.

www.lbl.gov

MX2 - Konkurrenz für Graphen

MoS2/WS2 heterostructure with a MoS2 monolayer lying on top of a WS2 monolayer. Electrons and holes created by light are shown to separate into different layers.