Qin Yang1 Deep Jariwala1 3 William Whitney1 Michelle Sherrott1 Cora Went1 Joeson Wong1 Yi-Rung Lin1 Wanyi Nie2 Aditya Mohite2 Harry Atwater1

1, California Institute of Technology, Pasadena, California, United States
3, University of Pennsylvania, Philadelphia, Pennsylvania, United States
2, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

Heterostructures constructed from two-dimensional (2D) van der Waals materials such as transition metal dichalcogenides (TMD), graphene, and boron nitride, have sparked wide interest in both device physics and materials science.1 Apart from these inorganic 2D materials, two-dimensional organic-inorganic hybrid lead halide perovskites (2D PVSKs) have recently emerged as promising materials for solar cells, with power conversion efficiencies over 12% and stability over 2000 hours, compared to 10 hours for traditional 3D PVSKs.2 2D PVSKs also show higher photoluminescence quantum yield (~26%) than their 3D counterparts (<1%), suggesting their intrinsic optoelectronic quality may be much higher.3

Fundamental discovery of 2D PVSK materials can be enabled by building a heterostructure with TMDs. In this study, we obtain evidence of the formation of interlayer excitons in 2D PVSK-TMD heterostructures through photoluminescence spectroscopy. Interlayer excitons are bound electron-hole pairs that live across the interface between two disparate materials, rather than being localized in an individual monolithic material. We find that the photoluminescence spectra of a 2D PVSK/WS2 heterostructure shows a new peak at a longer wavelength (~680nm), signifying the existence of an interlayer exciton. Using ultraviolet photoemission spectroscopy as well as time-resolved photoluminescence spectroscopy, we performed a systematic study on the possible interlayer excitons that can be formed between different 2D PVSKs and TMDs. Interlayer exciton observed in highly luminescent 2D PVSKs may provoke further studies of Van der Waals heterostructures, with novel applications in atomically thin solar cells, light-emitting diodes, and lasers.

1. Rivera, P. et al. Observation of long-lived interlayer excitons in monolayer MoSe2–WSe2 heterostructures. Nat. Commun. 6, 6242 (2015).
2. Tsai, H. et al. High-efficiency two-dimensional Ruddlesden–Popper perovskite solar cells. Nature 536, 312–316 (2016).
3. Dou, L. et al. Atomically thin two-dimensional organic-inorganic hybrid perovskites. Science 349, 1518–1521 (2015).