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Intrinsic quantum confinement in formamidinium lead triiodide perovskite

Abstract

Understanding the electronic energy landscape in metal halide perovskites is essential for further improvements in their promising performance in thin-film photovoltaics. Here, we uncover the presence of above-bandgap oscillatory features in the absorption spectra of formamidinium lead triiodide thin films. We attribute these discrete features to intrinsically occurring quantum confinement effects, for which the related energies change with temperature according to the inverse square of the intrinsic lattice parameter, and with peak index in a quadratic manner. By determining the threshold film thickness at which the amplitude of the peaks is appreciably decreased, and through ab initio simulations of the absorption features, we estimate the length scale of confinement to be 10–20 nm. Such absorption peaks present a new and intriguing quantum electronic phenomenon in a nominally bulk semiconductor, offering intrinsic nanoscale optoelectronic properties without necessitating cumbersome additional processing steps.

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Fig. 1: Temperature-dependent absorption coefficient and peak features.
Fig. 2: Temperature dependence of the optoelectronic and lattice properties of FAPbI3.
Fig. 3: Estimating the length scale of the structures inducing confinement.

Data availability

The datasets generated during and/or analysed during the current study are available in the Oxford University Research Archive repository50.

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Acknowledgements

This work was supported by the Engineering and Physical Sciences Research Council, the EPSRC Center for Doctoral Training in New and Sustainable Photovoltaics, the Chaire de Recherche Rennes Metropole project and the Robert A. Welch Foundation under award number F-1990-20190330.

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Contributions

A.D.W. performed the FTIR experiments, data analysis and participated in the experimental planning. G.V. carried out the first-principles calculations. J.B. prepared the samples. C.L.D. provided support with the FTIR experiments and data analysis. The project was conceived, planned and supervised by F.G., M.B.J. and L.M.H. A.D.W. wrote the first version of the manuscript and all authors contributed to the discussion and preparation of the final version of the article.

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Correspondence to Laura M. Herz.

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Supplementary Information

Supplementary Notes 1–15, Figs. 1–23, Table 1 and refs. 1–53.

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Wright, A.D., Volonakis, G., Borchert, J. et al. Intrinsic quantum confinement in formamidinium lead triiodide perovskite. Nat. Mater. 19, 1201–1206 (2020). https://doi.org/10.1038/s41563-020-0774-9

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