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Self-formed grain boundary healing layer for highly efficient CH3NH3PbI3 perovskite solar cells

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Abstract

Perovskite solar cells have attracted significant research efforts due to their remarkable performance, with certified power conversion efficiency now reaching 22%. Solution-processed perovskite thin films are polycrystalline, and grain boundaries are thought to be responsible for causing recombination and trapping of charge carriers. Here we report an effective and reproducible way of treating grain boundaries in CH3NH3PbI3 films deposited by means of a Lewis acid–base adduct approach. We show by high-resolution transmission electron microscopy lattice images that adding 6 mol% excess CH3NH3I to the precursor solution resulted in a CH3NH3I layer forming at the grain boundaries. This layer is responsible for suppressing non-radiative recombination and improving hole and electron extraction at the grain boundaries by forming highly ionic-conducting pathways. We report an average power conversion efficiency of 20.1% over 50 cells (best cell at 20.4%) together with significantly reduced current–voltage hysteresis achieved by this grain boundary healing process.

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Figure 1: Effects of excess CH3NH3I on film and photovoltaic parameters.
Figure 2: Grain and grain boundary analysis.
Figure 3: Photophysical characteristics for excess and deficient CH3NH3I.
Figure 4: c-AFM and photovoltaic performance.

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Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT Future Planning (MSIP) of Korea under contracts NRF-2012M3A6A7054861 and NRF-2014M3A6A7060583 (Global Frontier R&D Program on Center for Multiscale Energy System) and NRF-2012M3A7B4049986 (Nano Material Technology Development Program).

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Contributions

N.-G.P. conceived the experiments, performed data analysis and prepared the manuscript. H.S. performed high-resolution TEM and c-AFM and wrote the relevant part. D.K. performed time-resolved PL and TA spectroscopy and wrote the relevant part. D.-Y.S. and J.-W.L. prepared materials, fabricated devices and measured photovoltaic parameters. Y.J.C. performed time-resolved PL and TA. I.-H.J. performed photo-CELIV. S.L. performed TEM and c-AFM. P.J.Y. measured AFM images. N.A. measured SEM images. M.C. commented on the SEM results and edited the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Hyunjung Shin, Dongho Kim or Nam-Gyu Park.

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The authors declare no competing financial interests.

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Supplementary Figures 1–15, Supplementary Tables 1–4, Supplementary References. (PDF 1462 kb)

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Son, DY., Lee, JW., Choi, Y. et al. Self-formed grain boundary healing layer for highly efficient CH3NH3PbI3 perovskite solar cells. Nat Energy 1, 16081 (2016). https://doi.org/10.1038/nenergy.2016.81

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