Reversed Förster Resonance Energy Transfer in ReS2-Based Heterostructures

Energy transfer (ET) is central to energy-harvesting and optoelectronic technologies. Conventional Förster resonance energy transfer (FRET) requires substantial spectral overlap between donor emission and acceptor absorption and downhill energy flow. Here, we demonstrate an unconventional FRET process that operates without spectral overlap and enables energy transfer from lower-energy donors to higher-energy acceptors. In ReS2/hBN/TMD (TMD = WSe2, WS2, and MoS2) heterostructures, efficient ET occurs from ReS2 to TMD monolayers despite the lower excitonic energies of ReS2. This reversed FRET originates from high energy excitonic states at the K and M valleys of ReS2 arising from the band-nesting effect, as supported by transient absorption spectroscopy. As a result, over 30-fold photoluminescence enhancement, more than 63% transfer efficiency, and sub-80 ps transfer time are achieved, outperforming most reported systems. Our findings open an unexplored route for engineering interlayer energy flow and enhancing quantum yield low-dimensional materials.