Reduced defect density in triple and quadruple cation perovskite solar cells by incorporation of Cesium

Philipp Rieder^a, Yinghong Hu^b, Meltem F. Aygüler^b, Alexander G. Hufnagel^b, Michiel L. Petrus^b, Pablo Docampo^c, Kristofer Tvingstedt^a, Andreas Baumann^d, Thomas Bein^b, Vladimir Dyakonov^a^,^d

^aExperimental Physics VI, Julius Maximillian University of Würzburg, 97074 Würzburg, Germany

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

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

^dBavarian Center for Applied Energy Research, Magdalene-Schoch-Str. 3, 97074 Würzburg, Germany

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, Philipp Rieder, presentation 165
Publication date: 21st February 2018

Within the last years, the so-called mixed cation and halide ‘FAMA’ perovskite has replaced the archetype methylammonium lead iodide as the mainstay in the field of perovskite photovoltaics. Thereby, methylammonium (MA) and bromide is used to stabilize the crystal structure of formamidinium (FA) lead iodide perovskite. Recently, M. Saliba et al. further improved the stability of these state-of-the-art FAMA perovskite solar cells by introducing Cesium as well as Rubidium to the system, boosting the device power conversion efficiency up to 21.6%. [1]

In this work, we reveal the impact of Cs and/or Rb on the electronic properties of the FAMA perovskite crystal lattice by directly investigating the energetic landscape of electronic trap states via thermally stimulated current (TSC) spectroscopy on triple as well as quadruple cation perovskite solar cells. [2] In TSC, the device is cooled down in the dark well below the activation energy of possible trap states (here: T=30K). Subsequently, trap states are filled with charge carriers created by illumination. After a dwell time allowing charge carriers to relax into the trap states, the solar cell is heated up to 300K with a constant heat ramp, while the current is precisely measured. This current is attributed to charge carriers being released from previously occupied traps in the semiconductor, allowing to draw conclusions about their density and energetic distribution. For the study, the perovskite layer was altered between FAMA, FAMA with 5% of Cs, FAMA with 5% of Rb and FAMA with 5% of Cs as well as Rb in planar type solar cells with a layer sequence of FTO/SnO₂/perovskite/Spiro-OMeTAD/Au (from bottom to top). We found that while Rb had no significant influence on the trap landscape of FAMA, a controlled addition of Cs effectively lowers the trap density in FAMA-based devices, which can be directly linked to the higher performance observed in Cs containing perovskite solar cells

References

[1] M. Saliba, T. Matsui, K. Domanski et al., Science (2016), 354, 206-209

[2] Y. Hu, E.M. Hutter, P. Rieder et al., Adv. Energy Mater. 2018, 1703057

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