We investigate the electronic structure of solution-processed perovskite solar cells using temperature-dependent electroabsorption (EA) spectroscopy. Simultaneous measurements of absorption and electromodulated spectra of semitransparent methylammonium lead iodide solar cells facilitate a direct comparison of the specific features. The EA spectra can be transformed to peak-like line shapes utilizing an approach based on the Kramers–Kronig relations. The resulting peak positions correspond well to the discrete excitonic—rather than the continuum—contribution of the absorption spectra derived from generalized Elliott fits. This indicates the excitonic nature of the observed EA resonance and is found to be consistent over the whole temperature range investigated (from T = 10 K up to room temperature). To further confirm these findings, a line shape analysis of the measured EA spectra was performed. The best agreement was achieved using a first-derivative-like functional form which is expected for excitonic systems and supports the conclusion of an excitonic optical transition. Exciton binding energies EB are estimated for the orthorhombic and tetragonal phases as 26 meV and 19 meV, respectively. Nevertheless, power-conversion efficiencies η up to 13% (11.5% stabilized) demonstrate good charge-carrier separation in the devices due to sufficient thermal dissociation and Sommerfeld-enhanced absorption.
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Excitonic nature of optical transitions in electroabsorption spectra of perovskite solar cells
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19 February 2018
Research Article|
February 22 2018
Excitonic nature of optical transitions in electroabsorption spectra of perovskite solar cells

Fabian Ruf;
Fabian Ruf
1
Institute of Applied Physics, Karlsruhe Institute of Technology (KIT)
, 76131 Karlsruhe, Germany
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Alice Magin;
Alice Magin
1
Institute of Applied Physics, Karlsruhe Institute of Technology (KIT)
, 76131 Karlsruhe, Germany
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Moritz Schultes;
Moritz Schultes
2
Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)
, 70563 Stuttgart, Germany
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Erik Ahlswede;
Erik Ahlswede
2
Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)
, 70563 Stuttgart, Germany
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Heinz Kalt
;
Heinz Kalt
1
Institute of Applied Physics, Karlsruhe Institute of Technology (KIT)
, 76131 Karlsruhe, Germany
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Michael Hetterich
Michael Hetterich
1
Institute of Applied Physics, Karlsruhe Institute of Technology (KIT)
, 76131 Karlsruhe, Germany
3
Light Technology Institute, Karlsruhe Institute of Technology (KIT)
, 76131 Karlsruhe, Germany
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Appl. Phys. Lett. 112, 083902 (2018)
Article history
Received:
December 01 2017
Accepted:
January 31 2018
Connected Content
A companion article has been published:
Perovskite solar cells reveal excitonic optical transitions
Citation
Fabian Ruf, Alice Magin, Moritz Schultes, Erik Ahlswede, Heinz Kalt, Michael Hetterich; Excitonic nature of optical transitions in electroabsorption spectra of perovskite solar cells. Appl. Phys. Lett. 19 February 2018; 112 (8): 083902. https://doi.org/10.1063/1.5017943
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