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Ti1–graphene single-atom material for improved energy level alignment in perovskite solar cells


Carbon-based perovskite solar cells (C-PSCs) are widely accepted as stable, cost-effective photovoltaics. However, C-PSCs have been suffering from relatively low power conversion efficiencies (PCEs) due to severe electrode-related energy loss. Herein, we report the application of a single-atom material (SAM) as the back electrode in C-PSCs. Our Ti1–rGO consists of single titanium (Ti) adatoms anchored on reduced graphene oxide (rGO) in a well-defined Ti1O4-OH configuration capable of tuning the electronic properties of rGO. The downshift of the Fermi level notably minimizes the series resistance of the carbon-based electrode. By combining with an advanced modular cell architecture, a steady-state PCE of up to 20.6% for C-PSCs is finally achieved. Furthermore, the devices without encapsulation retain 98% and 95% of their initial values for 1,300 h under 1 sun of illumination at 25°C and 60 °C, respectively.

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Fig. 1: Structural characterizations of Ti1–rGO.
Fig. 2: Coordination structure analysis of Ti atom in Ti1–rGO.
Fig. 3: Mechanistical insight into tuning the electric properties of Ti1–rGO electrode.
Fig. 4: Photovoltaic performance and operational stability.

Data availability

The datasets analysed and generated during the current study are included in the paper and its Supplementary Information. Source data are provided with this paper.


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This work was financially supported by the National Natural Science Foundation of China (grant nos. 51872036, 51773025, 11504046), LiaoNing Revitalization Talents Program (grant nos. XLYC2007038, XLYC2008032), Dalian science and technology innovation fund (grant nos. 2018J12GX033, 2019J12GX032) and special funds for science and technology development under the guidance of the central government (grant no. 2021JH6/10500152). N.W. thanks the financial support from the Hong Kong Research Grants Council (project nos. 16306818 and N_HKUST624/19). C.Zhang thanks the Chinese Scholarship Council for their financial support to his in-split PhD study in Switzerland. M.G. thanks the financial support from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 881603.

Author information

Authors and Affiliations



Y.S. and C.Zhang proposed the idea, designed the project and organized the manuscript, C.Zhang carried out the experiments including material characterizations, device fabrication and measurements. M.G. supervised the experimental investigation and manuscript modification. C.Zhu contributed to material design, STEM characterization, structure analysis and manuscript preparation. W.L. conducted XANES and EXAFS measurements and analysed the chemical structure of Ti1–rGO. S.L. prepared Ti1–rGO and conducted DFT calculations. F.T.E. conducted and interpreted the JscVoc measurements. X.C. and N.W. conducted and interpreted the EELS characterization. S.M.Z. helped on manuscript organization and project coordination. K.Z. conducted the HTEM, EDX mapping characterizations and XAFS measurements. J.B. contributed to the analysis of the characterizations around interface. H.Z. helped on the device fabrication. Z.W. modified the manuscript. J.Z analysed the chemical structure of Ti1–rGO. Y.W. contributed to mechanical pressure measurement. J.H., C.X. and H.M. helped with material preparations and XPS/UPS characterizations. All authors contributed to results discussion and writing.

Corresponding authors

Correspondence to Chao Zhu, Michael Grätzel or Yantao Shi.

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The authors declare no competing interests.

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Peer review information Nature Energy thanks Andreas Hinsch and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–21, Notes 1–6 and Tables 1–8.

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Source data

Source Data Fig. 2

Numerical data used to generate Fig. 2.

Source Data Fig. 3

Numerical data used to generate Fig. 3a–e.

Source Data Fig. 4

Numerical data used to generate Fig. 4b–g.

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Zhang, C., Liang, S., Liu, W. et al. Ti1–graphene single-atom material for improved energy level alignment in perovskite solar cells. Nat Energy 6, 1154–1163 (2021).

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