Contribution to a conference proceedings/Contribution to a book

FZJ-2017-01377

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png In situ TEM analysis of structural changes in metal-halide perovskite solar cells under electrical bias

Jeangros, Q. (Corresponding author) ; Duchamp, M. ; Werner, J. ; Dunin-Borkowski, R.FZJ* ; Niesen, B. ; Ballif, C. ; Hessler-Wyser, A.

2016
Wiley-VCH Verlag GmbH & Co. KGaA Weinheim, Germany

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Please use a persistent id in citations: doi:10.1002/9783527808465.EMC2016.6370

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.

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Contributing Institute(s):

1. Mikrostrukturforschung (PGI-5)
2. Physik Nanoskaliger Systeme (ER-C-1)

Research Program(s):

1. 143 - Controlling Configuration-Based Phenomena (POF3-143) (POF3-143)

Appears in the scientific report 2016

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