Juyoung Leem1 Pilgyu Kang1 3 Jihun Mun2 Yeageun Lee1 Sang-Woo Kang2 SungWoo Nam1

1, University of Illinois at Urbana Champaign, Urbana, Illinois, United States
3, George Mason University, Fairfax, Virginia, United States
2, Korea Research Institute of Standards and Science, Daejeon, , Korea (the Republic of)

Atomically thin semiconducting materials are a promising platform for optoelectronic applications owing to their optical, electronic, and mechanical properties. Monolayer molybdenum disulfide (MoS2) is one of the most widely investigated materials for photosensors due to its direct bandgap. However, the low optical absorption of monolayer MoS2, resulting from its single atom thickness, limits higher photosensitivity. We present a mechanically self-assembled, crumpled MoS2 photodetector which achieves higher photosensitivity through structural deformation. The three-dimensional architecture of the crumpled structure offers several advantages including (i) enhanced sensitivity from material densification, (ii) high mechanical stretchability permitted by relaxation of the crumpled structure, and (iii) strain-induced reduction of the direct bandgap and funneling of photogenerated excitons. We further used graphene as electrical contacts to the crumpled MoS2 channel as graphene provides mechanical robustness by forming a van der Waals interface with MoS2. Our crumpled MoS2 photodetector exhibited an order of magnitude higher photosensitivity compared to a flat MoS2 photodetector. In addition, the photodetector is stretchable up to 200% without introducing major structural damage, verified by a durability test with 1000 cycles of stretching-releasing. Our approach to mechanical self-assembly of atomically thin semiconductors offers a simple but powerful way to enhance photosensitivity and potentially engineer exciton generation and funneling in two-dimensional materials.