Abstract
Stacking order in van der Waals materials determines the coupling between atomic layers and is therefore the key to materials’ properties. Recently, ferroelectricity, a phenomenon exhibiting reversible spontaneous electrical polarization, has been observed in zero-degree aligned van der Waals structures. In these artificial stacks, the single-domain size is limited by angle misalignment. Here we show that naturally rhombohedrally stacked MoS2 can host a homogeneous spontaneous polarization throughout the exfoliated flakes, free of misalignment. Utilizing this homogeneous polarization and its induced depolarization field, we build a graphene–MoS2-based photovoltaic device with high efficiency. Few-layer MoS2 is thinner than most oxide-based ferroelectric films, which allows us to maximize the depolarization field and study its impact at the atomically thin limit, whereas the highly uniform polarization in the commensurate crystal enables a tangible path for upscaling. The external quantum efficiency of our device is up to 16% at room temperature, over one order larger than the highest efficiency observed in bulk photovoltaic devices, owing to the reduced screening in graphene, exciton-enhanced light–matter interaction and ultrafast interlayer relaxation. Our findings make rhombohedral transition metal dichalcogenides a promising candidate for applications such as energy-efficient photodetection with high speed and programmable polarity.
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Data availability
Source data are provided with this paper. The data that support the plots within this paper and other findings of this study are available via Zenodo at https://doi.org/10.5281/zenodo.6416128.
Code availability
The codes that support the plots within this paper and other findings of this study are available via Zenodo at https://doi.org/10.5281/zenodo.6416128.
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Acknowledgements
Z.Y., D.Y., J.W., J.L., B.T.Z., M.F., T.S. and K.M.A. acknowledge support from the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, New Frontiers in Research Fund, Canada First Research Excellence Fund and Max Planck-UBC-UTokyo Centre for Quantum Materials. Z.Y. is also supported by the Canada Research Chairs Program. B.T.Z. and M.F. acknowledge Quantum Materials and Future Technologies Program, and the Croucher Foundation. Y.I. acknowledges support from JSPS Grant-in-Aid for Scientific Research (S) (JP19H05602) and the A3 Foresight Program. T.I. acknowledges Grant-in-Aid for Scientific Research on Innovative Areas (JP20H05264), Grant-in-Aid for Scientific Research (B) (JP19H01819) and JST PRESTO (JPMJPR19L1). K.W. and T.T. acknowledge support from JSPS KAKENHI (grant nos. 19H05790, 20H00354 and 21H05233). We would like to thank J. Dadap, Z. Wang, J. Folk, D. Jones, G. Sawatzky, A. Damascelli and T. Cao for helpful discussion.
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Z.Y. and D.Y. conceived this work. D.Y., T.S., J.W. and K.M.A. fabricated the sample. D.Y., J.W. and J.L. conducted the measurement under supervision from Z.Y. B.T.Z. performed the theoretical calculation under supervision from M.F. and Z.Y. T.I., Y.I., K.W. and T.T. provided the bulk crystal. Z.Y., D.Y. and J.W. analysed the data. Z.Y. and D.Y. wrote the manuscript based on inputs from all the other authors.
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Extended data
Extended Data Fig. 1 Thermal Background of Photocurrent.
Extracted thermal contributions of the AB (top panel) and BA (bottom panel) domains. The straight lines with negative slopes are due to the bolometric effect IBOL, which crosses zero at zero bias. The non-zero intercept is caused by the photo-thermal electric effect IPTE, which is opposite in direction to IPV. The IPTE is approximately independent with bias.
Extended Data Fig. 2 Photocurrent I-V curve of 2H Bilayer.
Bias dependence of photocurrent in the 2H bilayer device, C1. With a similar laser illumination condition (P=20 μW), C1 shows a nearly zero photocurrent at zero bias. The photocurrent linearly increases with bias, with no thermal contribution observed.
Supplementary information
Supplementary Information
Supplementary Figs. 1–11, Sections 1–15 and refs. 1–29.
Source data
Source Data Fig. 1
Experimental source data.
Source Data Fig. 2
Experimental source data.
Source Data Fig. 3
Experimental source data.
Source Data Fig. 4
Simulation results and experimental source data.
Source Data Extended Data Fig. 1
Extracted data from the global fitting in Fig. 3.
Source Data Extended Data Fig. 2
Experimental source data.
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Yang, D., Wu, J., Zhou, B.T. et al. Spontaneous-polarization-induced photovoltaic effect in rhombohedrally stacked MoS2. Nat. Photon. 16, 469–474 (2022). https://doi.org/10.1038/s41566-022-01008-9
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DOI: https://doi.org/10.1038/s41566-022-01008-9
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