The Influence of Fermi Level Alignment with Tin Oxide on the Hysteresis of Perovskite Solar Cells

Meltem F. Ayguler^a, Alexander G. Hufnagel^a, Philipp Rieder^b, Michael Wussler^c, Wolfram Jaegermann^c, Thomas Bein^a, Vladimir Dyakonov^b^,^d, Michiel L. Petrus^a, Andreas Baumann^d, Pablo Docampo^e

^aUniversity of Munich (LMU), Department of Chemistry and Center for Nanoscience (CeNS), 81377 Múnich, Alemania, Múnich, Germany

^bExperimental Physics VI, Julius-Maximilians-University of Würzburg, Am Hubland, Würzburg, 97074, Germany

^cTechnische Universität Darmstadt, Institut für Materialwissenschaft, Darmstadt

^dBavarian Center for Applied Energy Research (ZAE Bayern), Haberstr. 2a, 91058 Erlangen, Germany

^eSchool of Electrical and Electronic Engineering, Newcastle University, Merz court, NE1 7RU, Newcastle upon Tyne, United Kingdom

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)

Benidorm, Spain, 2018 May 28th - 31st

Organizers: Emilio Palomares and Rene Janssen

Oral, Meltem F. Ayguler, presentation 025
DOI: https://doi.org/10.29363/nanoge.hopv.2018.025
Publication date: 21st February 2018

The performance of perovskite solar cells (PSCs) has skyrocketed in recent years, but the devices still suffer from unreliable performance in the form of anomalous hysteresis. Although this concern has been linked to several processes such as ion migration in perovskite layer, trapping electronic carriers at the interfaces and ferroelectric polarization, none of these reasons fully explain the hysteresis in solar cells. On the other hand, recent studies showed that the combination of ion migration and charge recombination is required to achieve hysteresis in current-voltage characteristics. Therefore, Fermi level alignment between charge extraction layers and perovskite is important to prevent charge accumulation, causing charge recombination.
Here, we tune the Fermi level alignment between the electron transport layer (ETL) consisting of atomic layer deposited tin oxide, SnOX, and the perovskite absorber, Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3, by annealing of the ETL and highlight that this parameter is interlinked with current-voltage hysteresis in PSCs. Furthermore, thermally stimulated current (TSC) measurements reveal that the depth of trap states of the ETL correlates with Fermi level positions extracted from ultra-violet photoelectron spectroscopy (UPS), ultimately linking it to the energy difference between the Fermi level and conduction band maximum. In the presence of deep trap states, charge accumulation at the interface is promoted, causing charge recombination which increases the hysteresis of the solar cells. Thus, we believe that our work will shed light on the serious impediment of PSCs.

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