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Nat Commun. 2018 Aug 17;9(1):3301. doi: 10.1038/s41467-018-05583-w.

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance.

Author information

1
Perovtronics Research Center, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulsan, Ulju-gun, 44919, Korea.
2
Department of Materials & Interface, Weizmann Institute of Science, 7610001, Rehovot, Israel.
3
Division of Advanced Materials, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-Ro, Yuseong-Gu, Daejeon, 34114, Korea.
4
Beamline Research Division, Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), Pohang, 37673, Korea.
5
Department of Physics, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea.
6
UNIST Central Research Facilities & School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulsan, Ulju-gun, 44919, Korea.
7
Department of Materials & Interface, Weizmann Institute of Science, 7610001, Rehovot, Israel. gary.hodes@weizmann.ac.il.
8
Department of Materials & Interface, Weizmann Institute of Science, 7610001, Rehovot, Israel. david.cahen@weizmann.ac.il.
9
Perovtronics Research Center, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulsan, Ulju-gun, 44919, Korea. seoksi@unist.ac.kr.

Abstract

The presence of excess lead iodide in halide perovskites has been key for surpassing 20% photon-to-power conversion efficiency. To achieve even higher power conversion efficiencies, it is important to understand the role of remnant lead iodide in these perovskites. To that end, we explored the mechanism facilitating this effect by identifying the impact of excess lead iodide within the perovskite film on charge diffusion length, using electron-beam-induced current measurements, and on film formation properties, from grazing-incidence wide-angle X-ray scattering and high-resolution transmission electron microscopy. Based on our results, we propose that excess lead iodide in the perovskite precursors can reduce the halide vacancy concentration and lead to formation of azimuthal angle-oriented cubic α-perovskite crystals in-between 0° and 90°. We further identify a higher perovskite carrier concentration inside the nanostructured titanium dioxide layer than in the capping layer. These effects are consistent with enhanced lead iodide-rich perovskite solar cell performance and illustrate the role of lead iodide.

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