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@INPROCEEDINGS{Jeangros:827179,
author = {Jeangros, Quentin and Duchamp, Martial and Werner,
Jérémie and Dunin-Borkowski, Rafal and Niesen, Björn and
Ballif, Christophe and Hessler-Wyser, Aïcha},
title = {{I}n situ {TEM} analysis of structural changes in
metal-halide perovskite solar cells under electrical bias},
address = {Weinheim, Germany},
publisher = {Wiley-VCH Verlag GmbH $\&$ Co. KGaA},
reportid = {FZJ-2017-01377},
pages = {804 - 805},
year = {2016},
comment = {European Microscopy Congress 2016: Proceedings},
booktitle = {European Microscopy Congress 2016:
Proceedings},
abstract = {Organic-inorganic metal-halide perovskite solar cells are
emerging as a promising photovoltaic technology to harvest
solar energy, with latest efficiencies now surpassing
$22\%1$ - an impressive increase from the first reported
value of $3\%$ in 2009.2 In addition to low manufacturing
costs, the optical properties of such cells can be tailored
to form efficient tandems when combined with high-efficiency
silicon solar cells.3 A typical perovskite cell structure as
investigated here is based on a methylammonium lead
trihalide absorber (MAPbI3) that is placed between hole-
(Spiro-OMeTAD) and electron-selective contacts (a
fullerene-based material).While new record efficiencies are
frequently reported, the commercial application of this
solar cell technology remains hindered by issues related to
thermal and operational stability. Different mechanisms that
are still debated modify cell properties with time,
temperature, illumination and general operating conditions.4
In order to correlate applied voltage (V) and resulting
current (I) to changes in active layer chemistry and
structure on the nanometre scale, we performed both ex situ
and in situ transmission electron microscopy (TEM)
experiments, involving (scanning) TEM (STEM) imaging,
selected-area electron diffraction, energy-dispersive X-ray
spectroscopy and electron energy-loss spectroscopy. Samples
were prepared by focused ion beam (FIB) milling, with
exposure to air during transfer to the TEM minimised to <5
minutes to reduce any degradation of MAPbI3.First, the
effects of exposure to air and electron beam irradiation
were assessed in relation to FIB final thinning parameters.
Once adequate sample preparation and observation conditions
were identified, changes in morphology during cell
characterisation were assessed ex situ by comparing lamellae
extracted from as-manufactured and tested cells and then in
situ by contacting FIB-prepared samples to a
microelectromechanical systems (MEMS) chip mounted in a TEM
specimen holder5 (Fig. 1a). Cell manufacturing parameters
led to iodine diffusion into the hole collector, with the
width of this diffused layer remaining constant during I-V
characterisation. Similarly to ex situ experiments, the
MAPbI3/Spiro interface was observed to delaminate during in
situ electrical measurements, resulting in the presence of a
~5 nm Pb-rich layer on the hole-transparent-layer side
(Figs. 1b-c). In addition, PbI2 nanoparticles were observed
to nucleate within the MAPbI3 layer at the hole-collector
interface and at the positions of structural defects (Figs.
1b-d).Overall, the active MAPbI3 layer was observed to be
sensitive to sample preparation, exposure to air,
observation conditions and I-V stimulus, resulting in the
need for great care to deconvolute each effect. Different
mechanisms that may all contribute to the decrease in
efficiency of the cell were identified both ex situ and in
situ, including ionic migration, PbI2 formation and local
delamination of interfaces.},
month = {Aug},
date = {2016-08-28},
organization = {16th European Microscopy Congress (EMC
2016), Lyon (France), 28 Aug 2016 - 2
Sep 2016},
cin = {PGI-5 / ER-C-1},
cid = {I:(DE-Juel1)PGI-5-20110106 / I:(DE-Juel1)ER-C-1-20170209},
pnm = {143 - Controlling Configuration-Based Phenomena (POF3-143)},
pid = {G:(DE-HGF)POF3-143},
typ = {PUB:(DE-HGF)8 / PUB:(DE-HGF)7},
doi = {10.1002/9783527808465.EMC2016.6370},
url = {https://juser.fz-juelich.de/record/827179},
}