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It Takes Two to TangoDouble-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis
Version 2 2017-05-09, 14:21
Version 1 2017-05-08, 17:51
journal contribution
posted on 2017-04-24, 00:00 authored by Lukas Kegelmann, Christian M. Wolff, Celline Awino, Felix Lang, Eva L. Unger, Lars Korte, Thomas Dittrich, Dieter Neher, Bernd Rech, Steve AlbrechtSolar
cells made from inorganic–organic perovskites have gradually
approached market requirements as their efficiency and stability have
improved tremendously in recent years. Planar low-temperature processed
perovskite solar cells are advantageous for possible large-scale production
but are more prone to exhibiting photocurrent hysteresis, especially
in the regular n–i–p structure. Here, a systematic characterization
of different electron selective contacts with a variety of chemical
and electrical properties in planar n–i–p devices processed
below 180 °C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM
structure are used as electron transport materials (ETMs). Perovskite
layers deposited atop the different ETMs with the herein applied fabrication
method show a similar morphology according to scanning electron microscopy.
Further, surface photovoltage spectroscopy measurements indicate comparable
perovskite absorber qualities on all ETMs, except TiO2,
which shows a more prominent influence of defect states. Transient
photoluminescence studies together with current–voltage scans
over a broad range of scan speeds reveal faster charge extraction,
less pronounced hysteresis effects, and higher efficiencies for devices
with fullerene compared to those with metal oxide ETMs. Beyond this,
only double-layer ETM structures substantially diminish hysteresis
effects for all performed scan speeds and strongly enhance the power
conversion efficiency up to a champion stabilized value of 18.0%.
The results indicate reduced recombination losses for a double-layer
TiO2/PCBM contact design: First, a reduction of shunt paths
through the fullerene to the ITO layer. Second, an improved hole blocking
by the wide band gap metal oxide. Third, decreased transport losses
due to an energetically more favorable contact, as implied by photoelectron
spectroscopy measurements. The herein demonstrated improvements of
multilayer selective contacts may serve as a general design guideline
for perovskite solar cells.
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Transient photoluminescence studiespower conversion efficiencydouble-layer ETM structuresfullerene derivatives C 60ICMAPCBMelectron transport materialsfabrication method showReduced Hysteresis Solar cellssurface photovoltage spectroscopy measurementsPerovskite Solar Cellsscanning electron microscopyITOmetal oxides TiO 2hysteresis effectsscan speedsmetal oxide ETMsdeviceperovskite absorber qualitiesband gap metal oxidecontactphotoelectron spectroscopy measurements
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