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Direct–indirect character of the bandgap in methylammonium lead iodide perovskite

Nature Materials volume 16, pages 115–120 (2017)Cite this article

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Abstract

Metal halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) are generating great excitement due to their outstanding optoelectronic properties, which lend them to application in high-efficiency solar cells and light-emission devices. However, there is currently debate over what drives the second-order electron–hole recombination in these materials. Here, we propose that the bandgap in CH3NH3PbI3 has a direct–indirect character. Time-resolved photo-conductance measurements show that generation of free mobile charges is maximized for excitation energies just above the indirect bandgap. Furthermore, we find that second-order electron–hole recombination of photo-excited charges is retarded at lower temperature. These observations are consistent with a slow phonon-assisted recombination pathway via the indirect bandgap. Interestingly, in the low-temperature orthorhombic phase, fast quenching of mobile charges occurs independent of the temperature and photon excitation energy. Our work provides a new framework to understand the optoelectronic properties of metal halide perovskites and analyse spectroscopic data.

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Figure 1: Representation of TRPL and TRMC measurements on a thin film of CH3NH3PbI3.
Figure 2: Photo-conductance for a CH3NH3PbI3 thin film.
Figure 3: Product of generation yield φ (≤1) and mobility Σμ as a function of temperature in a CH3NH3PbI3 thin film.
Figure 4: Temperature-dependent PL and TRMC kinetics.
Figure 5: Proposed band diagram and activation energy for second-order recombination in the CH3NH3PbI3 thin film.

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Acknowledgements

This work was supported by the Netherlands Organization for Scientific Research (NWO) under the Echo grant number: 712.014.007. S.D.S. has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement number PIOF-GA-2013-622630. The authors thank A. Houtepen, A. Achtstein and D. deQuilettes for fruitful discussions. W. Evers is acknowledged for technical assistance.

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Authors and Affiliations

  1. Department of Chemical Engineering, Opto-electronic Materials Section, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands

    Eline M. Hutter, María C. Gélvez-Rueda, Ferdinand C. Grozema & Tom J. Savenije

  2. Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    Anna Osherov, Vladimir Bulović & Samuel D. Stranks

  3. Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK

    Samuel D. Stranks

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Contributions

E.M.H. performed and analysed the photon-induced TRMC, optical absorption and (TR)PL measurements under the supervision of T.J.S. S.D.S. prepared the samples and performed additional optical absorption measurements. A.O. performed XRD and SEM measurements under the supervision of V.B., and M.C.G.-R. and F.C.G. performed pulse-radiolysis TRMC measurements. E.M.H. and T.J.S. conceived the idea and wrote the manuscript together with S.D.S.

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Correspondence to Samuel D. Stranks or Tom J. Savenije.

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Hutter, E., Gélvez-Rueda, M., Osherov, A. et al. Direct–indirect character of the bandgap in methylammonium lead iodide perovskite. Nature Mater 16, 115–120 (2017). https://doi.org/10.1038/nmat4765

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