Thermal and moisture stability of methylammonium lead iodide based perovskite solar cells
Ausra Morkunaite a, Thomas Schnabel a, Cordula Wessendorf a, Erik Ahlswede a
a Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), 70563 Stuttgart, Germany
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Thin Film Photovoltaics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Kai Zhu
Poster, Thomas Schnabel, 056
Publication date: 21st November 2018

Despite their impressive performance, the stability and especially the elution of lead is an important topic for perovskite solar cells. Since the absorber material methylammonium lead iodide (MAPI) is known to be highly unstable against heat and humidity[1] and lead causes severe health hazards[2], it has to be protected against environmental influence.

In this work, the stability of MAPI against water was tested with different levels of protection. After investigating the lead elution kinetics of a bare MAPI layer by UV-Vis absorption spectrometry, different barrier layers such as MoOx and Al2O3 were applied. Especially an only 2 nm thick Al2O3 layer could slow down the lead elusion by a factor of 2.

In a next step closer to an actual solar cell device, Spiro-OMeTAD, P3HT and CuSCN were investigated as hole transport materials (HTM) concerning their effect on the lead elution. Spiro-OMeTAD showed the best protective effect, which could even be improved when combined with the Al2O3 barrier.

Furthermore, Polymethylmethacrylate (PMMA) was applied as hydrophobic coating on top of a MAPI layer. Since it showed a drastic increase in stability at room temperature, it was additionally tested in liquid water at 85 °C. Besides the improved stability it was shown, that the PMMA coating only slightly reduces the efficiency of solar cells (a decrease from 13 to 11 % was observed), which makes it a very promising concept.

Finally, four different encapsulation designs were compared to protect the MAPI layer from environmental influences. The combination of an edge sealing containing butyl bromide and a polymeric encapsulation foil showed the best protection. After a damp heat test for 96 h no degradation of the MAPI layer was visible and no lead elution could be detected.

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