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Download fileAnticorrelation between Local Photoluminescence and Photocurrent Suggests Variability in Contact to Active Layer in Perovskite Solar Cells
journal contribution
posted on 2016-10-17, 15:18 authored by Giles
E. Eperon, David Moerman, David S. GingerWe use high-resolution, spatially
resolved, laser beam induced
current, confocal photoluminescence, and photoconductive atomic force
microscopy (pcAFM) measurements to correlate local solar cell performance
with spatially heterogeneous local material properties in methylammonium
lead triiodide (CH3NH3PbI3) perovskite
solar cells. We find that, for this material and device architecture,
the photocurrent heterogeneity measured via pcAFM
on devices missing a top selective contact with traditional Au-coated
tips is significantly larger than the photocurrent heterogeneity observed
in full devices with both electron- and hole-selective extraction
layers, indicating that extraction barriers at the Au/perovskite interface
are ameliorated by deposition of the organic charge extraction layer.
Nevertheless, in completed, efficient device structures (PCE ≈
16%) with state-of-the-art nickel oxide and [6,6]-phenyl-C61-butyric
acid (PCBM) methyl ester contacts, we observe that the local photoluminescence
(PL) is weakly anticorrelated with local photocurrent at both short-circuit
and open-circuit conditions. We determine that the contact materials
are fairly homogeneous; thus the heterogeneity stems from the perovskite
itself. We suggest a cause for the anticorrelation as being related
to local carrier extraction heterogeneity. However, we find that the
contacts are still the dominating source of losses in these devices,
which minimizes the impact of the material heterogeneity on device
performance at present. These results suggest that further steps to
prevent recombination losses at the interfaces are needed to help
perovskite-based cells approach theoretical efficiency limits; only
at this point will material heterogeneity become crucial.