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Nature Nanotechnology (2026)
Atomically thin semiconductor junctions offer a platform for probing optoelectronic processes beyond the continuum limit, where reduced screening and strong exciton binding make local fields especially important for charge separation. Yet it remains unclear how individual dopants contribute to the photovoltaic response when the junction thickness becomes comparable with the atomic length scales and smaller than conventional depletion or diffusion lengths. Here we demonstrate this concept by probing the microscopic photoresponse of a van der Waals semiconductor homobilayer containing ionizing acceptors. Using photoconductive atomic force microscopy on vanadium-doped WSe2 (V:WSe2) bilayers, we directly visualize nanometre-scale photocurrent hotspots centred on single dopants, which have opposite current polarities for dopants in the top and bottom layers. Vertical WSe2/V:WSe2 homobilayer devices show that the macroscopic photocurrent scales linearly with dopant concentration and exhibits a compensation voltage that is independent of illumination power and dopant density, in contrast to bulk homojunction devices. Photocurrent spectroscopy and quasi-classical modelling indicate that charged dopants locally convert tightly bound intralayer excitons into charge-separated interlayer states, thereby enabling efficient exciton dissociation within a region of about 1 nm. These results establish dopant-defined point-like junctions as the elementary photovoltaic units in atomically thin homobilayers.
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The data supporting the findings of this study are available within the article and its Supplementary Information. Additional information can be obtained from the corresponding authors upon request.
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G.E. discloses support for the research of this work from the Ministry of Education), Singapore, under AcRF Tier 2 (T2EP50124-0025) and Tier 1 (A-8001995-00-00). M.T. discloses support for the research of this work from Ministry of Education, Singapore, under its Research Center of Excellence award to the Institute for Functional Intelligent Materials (Project No. EDUNC-33-18-279-V12). Q.W. and L.K.A. disclose support for the research of this work from Singapore A*STAR IRG (Grant No. M23M6c0102). I.V. discloses support for the research of this work from Singapore National Research Foundation under its Thematic Competitive Research Programme (Grant No. NRF-T-CRP-2025-0007). K.W. and T.T. disclose support for the research of this work from the JSPS (KAKENHI Grant Nos. 21H05233 and 23H02052), CREST (Grant No. JPMJCR24A5), JST and the World Premier International Research Center Initiative, MEXT, Japan. The other authors declare no relevant funding.
Physics Department, National University of Singapore, Singapore, Singapore
Nam Thanh Trung Vu, Yi Wei Ho, Cheng Quan Wong, Yuan Chen, Adam K. Budniak, Leyi Loh & Goki Eda
Chemistry Department, National University of Singapore, Singapore, Singapore
Mingjun Chen & Goki Eda
Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
Yi Wei Ho & Maxim Trushin
Science, Mathematics, and Technology, Singapore University of Technology and Design (SUTD), Singapore, Singapore
Qingyun Wu & Lay Kee Ang
Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore
Adam K. Budniak, Michel Bosman & Maxim Trushin
Quantum Innovation Centre (Q. InC), Agency for Science Technology and Research (A*STAR), Singapore, Republic of Singapore
Ivan Verzhbitskiy
Institute of Materials Research and Engineering (IMRE), Agency for Science Technology and Research (A*STAR), Singapore, Republic of Singapore
Ivan Verzhbitskiy
Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan
Kenji Watanabe
Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
Takashi Taniguchi
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G.E. and N.T.T.V. conceived the idea of the experiments. N.T.T.V. performed all the pcAFM experiments including sample fabrication. N.T.T.V. fabricated the photocurrent devices with the assistance of C.Q.W. and M.C. M.C. established the photocurrent measurement set-up. N.T.T.V. performed the photocurrent measurements with the assistance of M.C. Y.W.H. established and conducted the second-harmonic-generation measurements. Q.W. conducted and analysed the first-principles calculations under the supervision of L.K.A. A.K.B. and L.L. performed the STEM imaging and STEM statistical analyses under the supervision of M.B. Y.C. established and conducted the differential reflectance measurements and performed the complementary STEM experiments. A.K.B. and I.V. grew the undoped and doped WSe2 crystals. K.W. and T.T. provided the hBN crystals. M.T. provided theoretical support and devised the models. N.T.T.V., M.T. and G.E. analysed the experimental data. N.T.T.V., M.T. and G.E. wrote the paper, and M.C. prepared the figures with input from the other co-authors.
Correspondence to Nam Thanh Trung Vu, Maxim Trushin or Goki Eda.
The authors declare no competing interests.
Nature Nanotechnology thanks Ziliang Ye and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Vu, N.T.T., Chen, M., Ho, Y.W. et al. Point-like photovoltaic junction in 2D semiconductor homobilayer. Nat. Nanotechnol. (2026). https://doi.org/10.1038/s41565-026-02251-9
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