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Top and bottom surfaces limit carrier lifetime in lead iodide perovskite films

Nature Energy volume 2, Article number: 16207 (2017) Cite this article

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Abstract

Carrier recombination at defects is detrimental to the performance of solar energy conversion systems, including solar cells and photoelectrochemical devices. Point defects are localized within the bulk crystal while extended defects occur at surfaces and grain boundaries. If not properly managed, surfaces can be a large source of carrier recombination. Separating surface carrier dynamics from bulk and/or grain-boundary recombination in thin films is challenging. Here, we employ transient reflection spectroscopy to measure the surface carrier dynamics in methylammonium lead iodide perovskite polycrystalline films. We find that surface recombination limits the total carrier lifetime in perovskite polycrystalline thin films, meaning that recombination inside grains and/or at grain boundaries is less important than top and bottom surface recombination. The surface recombination velocity in polycrystalline films is nearly an order of magnitude smaller than that in single crystals, possibly due to unintended surface passivation of the films during synthesis.

Since 2009 polycrystalline lead halide perovskite thin films have become a phenomenon in photovoltaic research1, and now perovskite-based solar cells routinely exceed 20% power conversion efficiency2,3,4. The extraordinary photovoltaic performance is attributed to beneficial physical properties such as strong light absorption, long carrier lifetime5,6 and a large carrier diffusion coefficient5,7,8,9. These already remarkable properties are generally improved in single-crystal samples10,11,12,13. In addition, surface recombination is an essential property that directly impacts the photovoltaic performance. Any surface recombination can reduce the overall carrier lifetime14,15,16,17 and thereby reduce the conversion efficiency4. Furthermore, surface recombination plays an important role in other perovskite-based optoelectronic applications. For instance, fast surface recombination can be employed to design photodetectors18,19,20, while low surface recombination is required for lasers21,22 and light-emitting diodes23. Thus, the study of surface recombination is key for improving and expanding perovskite-based optoelectronic applications. However, in contrast to the thorough investigation of bulk recombination24,25,26,27,28, surface recombination in lead iodide perovskites has not been examined.

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Figure 1: Absorption coefficient 𝛼(ℏω) spectra.
Figure 2: Transient reflection measurements.
Figure 3: Surface and total carrier dynamics.
Figure 4: Surface kinetics with different pump-photon energies.

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Acknowledgements

K.Z. and M.Y. acknowledge the support by the hybrid perovskite solar cell programme of the National Center for Photovoltaics funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office. D.T.M. acknowledges the National Renewable Energy Laboratory Director’s Fellowship. Y.Yang, E.M.M. and M.C.B. acknowledge support from the Solar Photochemistry programme within the US. DOE, Office of Basic Sciences, Office of Science. Work at NREL was conducted under contract number DE-AC36-08G028308.

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  1. Ye Yang and Mengjin Yang: These authors contributed equally to this work.

Authors and Affiliations

  1. Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA

    Ye Yang, Mengjin Yang, David T. Moore, Yong Yan, Elisa M. Miller, Kai Zhu & Matthew C. Beard

  2. Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, USA

    Yong Yan

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Contributions

Y.Yang carried out the transient reflectance experiment; Y.Yang and M.C.B. analysed the data; E.M.M. carried out the XPS data collection and analysis; M.Y. and K.Z. prepared and characterized the thin-film samples; D.T.M. and Y.Yan prepared the single-crystal samples; Y.Yang and M.C.B. wrote the manuscript with input and discussion from all authors.

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Correspondence to Kai Zhu or Matthew C. Beard.

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Supplementary Figures 1–13, Supplementary Tables 1–3, Supplementary Notes 1–2 and Supplementary References. (PDF 2376 kb)

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Yang, Y., Yang, M., Moore, D. et al. Top and bottom surfaces limit carrier lifetime in lead iodide perovskite films. Nat Energy 2, 16207 (2017). https://doi.org/10.1038/nenergy.2016.207

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