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Ligand-assisted cation-exchange engineering for high-efficiency colloidal Cs1xFAxPbI3 quantum dot solar cells with reduced phase segregation

Abstract

The mixed caesium and formamidinium lead triiodide perovskite system (Cs1xFAxPbI3) in the form of quantum dots (QDs) offers a pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective oleic acid (OA) ligand-assisted cation-exchange strategy that allows controllable synthesis of Cs1xFAxPbI3 QDs across the whole composition range (x= 0–1), which is inaccessible in large-grain polycrystalline thin films. In an OA-rich environment, the cross-exchange of cations is facilitated, enabling rapid formation of Cs1xFAxPbI3 QDs with reduced defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that the QD devices exhibit substantially enhanced photostability compared with their thin-film counterparts because of suppressed phase segregation, and they retain 94% of the original PCE under continuous 1-sun illumination for 600 h.

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Fig. 1: Mechanism of ligand-assisted A-site cation-exchange reaction.
Fig. 2: Morphology and crystal structure of Cs1xFAxPbI3 QD.
Fig. 3: Photovoltaic performance of QD devices.
Fig. 4: Optoelectronic characteristics of QD thin films and VOC loss mechanism in QD devices.
Fig. 5: Stability of QD thin film and devices.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request.

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Acknowledgements

Financial support from the Australian Research Council Discovery Projects (ARC DPs) is appreciated. Y.B. acknowledges the support from UQ Development Fellowship and ARC DECRA Fellowship (DE190101351). We acknowledge the facilities and the scientific support from the Queensland node of the Australian National Fabrication Facility and Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, The University of Queensland. We also acknowledge the use of the facilities at the University of Wollongong Electron Microscopy Centre funded by the ARC (grant nos. LE0882813 and LE120100104). Y.D. acknowledges financial support from the ARC (grant nos. DP160102627, DP170101467 and FT180100585). All computations were undertaken on the supercomputers in National Computational Infrastructure (NCI) in Canberra, which is supported by the Australian Commonwealth Government, and Pawsey Supercomputing Centre in Perth, with funding from the Australian Government and the Government of Western Australia. P.M. is a Sêr Cymru II National Research Chair and A.A. a Sêr Cymru II Rising Star Fellow. The work at Swansea University was funded through the Sêr Cymru II (Welsh European Funding Office and European Regional Development Fund) Program ‘Sustainable Advanced Materials’. Financial support from National Natural Science Foundation of China (grant nos. 51629201 and 51825204) is also appreciated.

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Y.B., M.H. and L.W. conceived the project. L.W. and Y.B. supervised the work. M.H. synthesized the perovskite quantum dot materials, fabricated and characterized the QD thin films and devices with the assistance of S.D. Y.B. designed the experiments for understanding the ligand-assisted cation-exchange reaction mechanism and the role of surface ligands. S.Z., N.Z., A.A. and P.M. conducted the electrical and photophysical characterization of QD devices. L.R., N.C. and Y.D. performed the STEM study and analysis. J.L. and Y.W. conducted DFT calculations. M.G., M.L. and J.-H.Y. performed the cross-sectional TEM characterization. Y.Y. conducted the ion conductivity measurements. P.C. and D.H. fabricated perovskite thin films and devices. Y.B. drafted the manuscript with help from M.H., A.A., L.R., and J.L. L.W., P.M., G.L. and H.M.-C. revised the manuscript. All the authors discussed the results and commented on the manuscript.

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Correspondence to Yang Bai or Lianzhou Wang.

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Supplementary Figs. 1–22, Tables 1–4, Notes 1–6 and refs 1–7.

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Hao, M., Bai, Y., Zeiske, S. et al. Ligand-assisted cation-exchange engineering for high-efficiency colloidal Cs1xFAxPbI3 quantum dot solar cells with reduced phase segregation. Nat Energy 5, 79–88 (2020). https://doi.org/10.1038/s41560-019-0535-7

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