Unlike stacked graphene, semiconducting 2D transition metal dichalcogenides (TMDCs) have diffuse interlayer d-orbital overlap. To enhance interlayer electronic coupling in TMDCs, we apply an interlayer-directed E-field, inducing electron-hole dissociation as shown in Fig. 1b. Time-resolved photocurrents show that stacked WSe₂ devices shown in Fig. 1a can have both IQE >50% and fast (<60 ps) picosecond electron escape times. Our ultrafast photocurrent rates kinetics give the same E-field-dependent electronic escape and dissociation rates seen from ultrafast optical TA microscopy.[2] To rationalize these fast electronic escape rates, we show the ratio of the electronic rates accurately predicts the actual WSe₂ device photocurrent generation efficiency. Lastly, we will show how certain intermolecular twist angle packings of athraditiophene molecular crystals make electron-multiplication by singlet fission of TT states favorable. Singlet fission dynamics are indicated in Fig. 1c by the matching singlet (blue) vs. rising triplet dynamics (red) obtained when the probe polarization aligned along the crystal charge-transfer axis. However, other intermolecular packing angles (at 90^o) instead localize and trap excitons as excimers, preventing singlet fission.[3] These interlayer stacked systems collectively demonstrate how remarkably different interlayer electronic states evolve from relatively small changes in interlayer twist angles in van der Waals stacked materials and molecular singlet fission materials.

References
[1] H. Patel, L. Huang, C.J. Kim, J. Park, M. W. Graham, Stacking Angle-Tunable Photoluminescence from Interlayer Exciton States in Twisted Bilayer Graphene, Nature Comm, 10, 1445 (2019)
[2] K. T. Vogt, S.-F. Shi, F. Wang, M. W. Graham, Ultrafast photocurrent and absorption microscopy of few-layer TMD devices isolate rate-limiting dynamics driving fast and efficient photoresponse, J Phys Chem C, 124, 28, 15195–15204 (2020)
[3] G. Mayonado, K. T. Vogt, J. Van Schenck, O. Ostroverkhova, M. W. Graham, Packing Morphology-Dependent Singlet Fission in Single Crystal Anthradithiophene Derivatives, OSA Technical Digest: Ultrafast Phenomena, doi.org/10.1364/UP.2020.Th2A.4 (2020)