Abstract
Organic–inorganic metal halide perovskites have demonstrated high power conversion efficiencies in solar cells and promising performance in a wide range of optoelectronic devices. The existence and stability of bound electron–hole pairs in these materials and their role in the operation of devices with different architectures remains a controversial issue. Here we demonstrate, through a combination of optical spectroscopy and multiscale modelling as a function of the degree of polycrystallinity and temperature, that the electron–hole interaction is sensitive to the microstructure of the material. The long-range order is disrupted by polycrystalline disorder and the variations in electrostatic potential found for smaller crystals suppress exciton formation, while larger crystals of the same composition demonstrate an unambiguous excitonic state. We conclude that fabrication procedures and morphology strongly influence perovskite behaviour, with both free carrier and excitonic regimes possible, with strong implications for optoelectronic devices.
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Acknowledgements
The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 604032 of the MESO project, under grant agreement 316494 (DESTINY), the EU Horizon 2020 Research and Innovation Programme under grant agreement no. 643238 (SYNCHRONICS) and from Fondazione Cariplo (project GREENS no. 2013-0656). J.M.F. is funded by the EPSRC (EP/K016288/ and EP/M009580/1), and A.W. is supported by the European Research Council (project no. 277757). The authors thank S. Neutzner for help with fs-TA experiments and W. Xu for help with sample preparation. The authors thank E.T. Hoke, E.R. Dohner and H. Karunadasa for discussions and for providing the single crystal. The authors thank L. Manna for discussions and access to the XRD facility.
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G.G., A.R.S.K. and A.J.B. performed the transient absorption measurements. M.G. and M.D.B. prepared the samples and characterized them by SEM. S.M. performed XRD and SEM characterization. G.G., A.R.S.K., G.L. and A.P. analysed the optical spectroscopy data. J.M.F. and A.W. performed the multiscale modelling and analysed the results. The manuscript was written with contributions from all authors. A.P. supervised the project.
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Grancini, G., Srimath Kandada, A., Frost, J. et al. Role of microstructure in the electron–hole interaction of hybrid lead halide perovskites. Nature Photon 9, 695–701 (2015). https://doi.org/10.1038/nphoton.2015.151
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DOI: https://doi.org/10.1038/nphoton.2015.151
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