Thermoelectric and Photovoltaic Energy Conversion in Interlayer Exciton Structures

Excitons are bound electron and hole pairs. Recent spectroscopic and electronic transport<br/>measurements have observed potential Bose-Einstein condensation signatures of interlayer<br/>excitons in van der Waals heterostructures of transition metal dichalcogenides (TMDs).<br/>Thermoelectric measurement can provide unique insight into unusual collective energy<br/>transport behaviors associated with the bosonic nature of excitons. Here, we explore<br/>thermoelectric and photovoltaic measurements in two-dimensional TMDs heterostructures<br/>separated by a hexagonal boron nitride insulating layer. With their charge carrier<br/>concentration controlled by separate bottom and top gates, an n-type material and a p-type<br/>material can be connected electrically in series and thermally in parallel, similar to a<br/>thermoelectric couple. A lateral temperature gradient drives the diffusion of the electrons and<br/>holes from the hot side to the cold side, giving rise to a thermoelectric current. These<br/>thermoelectric and optoelectronic properties are measured at different combinations of the<br/>electron and hole concentrations to search for signatures of exciton binding and improved<br/>energy conversion.