Dual Effect of Positive and detrimental effects of humidity on cesium lead bromide
Diego De Girolamo a, Ibrahim M. Dar b, Danilo Dini a, Lorenzo Gontrani a, Ruggero Caminiti a, Alessandro Mattoni c, Michael Graetzel b, Simone Meloni d
a Dept. of Chemistry, Sapienza University of Rome
b Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechmique Fédérale de Lausanne, 1015 Lausanne, Switzerland
c c. Istituto Officina dei Materiali, CNR-IOM SLACS Cagliari, Cittadella Universitaria, Monserrato (CA) 09042, Italy
d Dept. of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, 00184, Rome, Italy
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Simone Meloni, 134
Publication date: 11th February 2019

Iodide-based perovskites have attracted much attention due to the high PCE achieved by solar cells fabricated using these materials. However, other perovskite systems are also attracting for many optoelectronics applications. For example, CsPbBr3 perovskite is highly desired to fabricate high photovoltage solar cells, tandem solar cells, light-emitting diodes, lasers, photodetectors, field effect transistors etc. The resistance to stressing agents of bromide perovskites is much less investigated than the corresponding iodide ones. In this talk I report our recent results on the effect of prolonged exposure (up to 500h) of CsPbBr3 to ~60% and 80% relative humidity by in-situ X-ray diffraction and ex-situ scanning electron microscopy and UV-visible spectroscopy. I show that humidity plays a dual role on CsPbBr3. Humidity is beneficial for short time exposure, producing an increase of perovskite content, an improvement of the film morphology and an enhancement of the UV-Vis absorbance. However, a prolonged exposure results in a partial degradation of the film, with corresponding worsening of its optoelectronic properties. At the end of exposure to humidity degradation process is incomplete. Moreover, degradation is partly reversible: upon restoration of ambient humidity one obtains a sample containing both CsPbBr3 and degradation products. By combining experiments and computer simulations we identified the degradation products and propose a degradation mechanism.

The authors thank the Sapienza Research Centre for Nanotehnologies Applied to Engineering, CNIS, for the access to the XRD experimental equipment used in this work. The authors acknowledge PRACE and ISCRA for awarding the access to resource MARCONI based in Italy at Casalecchio di Reno and Piz Daint based at the CSCS for the projects UNWRAP, UNWRAPIT and ADRENALINE.

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