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. 2020 Sep 3;11(17):7127-7132.
doi: 10.1021/acs.jpclett.0c01822. Epub 2020 Aug 18.

Understanding the Stability of MAPbBr3 versus MAPbI3: Suppression of Methylammonium Migration and Reduction of Halide Migration

Lucie McGovern  1 , Moritz H Futscher  1 , Loreta A Muscarella  1 , Bruno Ehrler  1
Affiliations

Understanding the Stability of MAPbBr3 versus MAPbI3: Suppression of Methylammonium Migration and Reduction of Halide Migration

Lucie McGovern et al. J Phys Chem Lett. .

Abstract

Solar cells based on metal halide perovskites often show excellent efficiency but poor stability. This degradation of perovskite devices has been associated with the migration of mobile ions. MAPbBr3 perovskite materials are significantly more stable under ambient conditions than MAPbI3 perovskite materials. In this work, we use transient ion drift to quantify the key characteristics of ion migration in MAPbBr3 perovskite solar cells. We then proceed to compare them with those of MAPbI3 perovskite solar cells. We find that in MAPbBr3, bromide migration is the main process at play and that contrary to the case of MAPbI3, there is no evidence for methylammonium migration. Quantitatively, we find a reduced activation energy, a reduced diffusion coefficient, and a reduced concentration for halide ions in MAPbBr3 compared to MAPbI3. Understanding this difference in mobile ion migration is a crucial step in understanding the enhanced stability of MAPbBr3 versus MAPbI3.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Inverted MAPbBr3 device characteristics. (a) Solar cell architecture of the full device, with the MAPbBr3 film sandwiched between a hole transport layer of NiOx and an electron transport layer of C60 and BCP. A fluoride tin oxide (FTO) bottom electrode and a gold top electrode complete the device, allowing for the extraction of the holes and electrons. (b) Top view SEM image of the MAPbBr3 perovskite layer showing 200–500 nm grains. (c) SEM cross-sectional image of the MAPbBr3 perovskite layer on top of FTO and NiOx. (d) Current–voltage characteristics measured in the dark and light, with a scan speed of 10 mV s–1.
Figure 2
Figure 2
(a) Capacitance transient measurements of a MAPbBr3 solar cell measured in the dark, with a DC voltage of 0 V and an AC voltage of 10 mV at 104 Hz, after applying a pulse of 1.1 V for 1 s. (b) Relative difference in capacitance ΔC = C(t) – C2.5 ms for the capacitance transients between 240 and 340 K. (c) Arrhenius plot showing the activation energy derived from this measurement.
Figure 3
Figure 3
Comparison of mobile ions in MAPbBr3 and MAPbI3 showing (a) a reduced activation energy for bromide migration, (b) a reduced diffusion coefficient for bromide migration (at 300 K), and (c) a reduced density of bromide mobile ions. Error bars are the standard deviations of the weighted means.
See this image and copyright information in PMC

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