Park, S.; Mutz, N.; Kovalenko, S.A.; Schultz, T.; Shin, D.; Aljarb, A.; Li, L.J.; Tung, V.; Amsalem, P.; List-Kratochvil, E.J.W.; Stähler, J.; Xu, X.; Blumstengel, S.; Koch, N.: Type-I Energy Level Alignment at the PTCDA-Monolayer MoS2 Interface Promotes Resonance Energy Transfer and Luminescence Enhancement. Advanced Science 8 (2021), p. 2100215/1-9
10.1002/advs.202100215
Open Access Version
Abstract:
Van der Waals heterostructures consisting of 2D semiconductors and conjugated molecules are of increasing interest because of the prospect of a synergistic enhancement of (opto)electronic properties. In particular, perylenetetracarboxylic dianhydride (PTCDA) on monolayer (ML)-MoS2 has been identified as promising candidate and a staggered type-II energy level alignment and excited state interfacial charge transfer have been proposed. In contrast, it is here found with inverse and direct angle resolved photoelectron spectroscopy that PTCDA/ML-MoS2 supported by insulating sapphire exhibits a straddling type-I level alignment, with PTCDA having the wider energy gap. Photoluminescence (PL) and sub-picosecond transient absorption measurements reveal that resonance energy transfer, i.e., electron–hole pair (exciton) transfer, from PTCDA to ML-MoS2 occurs on a sub-picosecond time scale. This gives rise to an enhanced PL yield from ML-MoS2 in the heterostructure and an according overall modulation of the photoresponse. These results underpin the importance of a precise knowledge of the interfacial electronic structure in order to understand excited state dynamics and to devise reliable design strategies for optimized optoelectronic functionality in van der Waals heterostructures.