In-situ spectroscopic study on structural stability of mixed halide perovskites MAPbX (X = I,Br,Cl)

Petra Cameron^a, Ralf Niemann^a, Athanassios Kontos^b, Polycarpos Falaras^b

^aUniversity of Bath, Bath BA2 7AY, United Kingdom, United Kingdom

^bInstitute of Nanoscience and Nanotechnology, NCSR Demokritos, Patriarchou Grigoriou & Neapoleos Str., Agia Paraskevi, Athens, 15310, Greece

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Ralf Niemann, 390
Publication date: 5th February 2015

The last few years have seen a surge in research into perovskite photvoltaics [1] with a steep rise in cell performances to a recently certified value of 20.1% [2]. To further advance this new material, a better insight into its intriguing properties needs to be gained in order to optimize its role in photovoltaic cells. Cooperative effects between structure, light harvesting ability, electron/hole mobility and photovoltaic behavior leave many questions open up to date [3]. Structural modifications via substitution of halides [4] or organic cations [5] in the perovskite have shown improvements in material stability and a potential to tune bandgap properties. However, the basic understanding of the interaction between structure, optoelectronic properties and stability remains mainly empirical. In this work the structure of mixed halide perovskite materials MAPbX (MA = methylammonium; X = I, Br, Cl) was studied with micro-Raman spectroscopy. Micro Raman spectroscopy has a lateral resolution below 1 μm and thus permits analysis of the phase homogeneity of the perovskite across the film. Furthermore it is an ideal technique in order to study the low frequency vibrational spectral region [6] including lattice modes of the inorganic cage and torsional modes of the organic MA cation, which are very sensitive to the nature of the anion. In addition, crystallization, disorder, orientation and insertion of the perovskite are also affected and these changes can influence the materials vibrational properties. Thus, structural changes during photo-induced decomposition were observed and monitored in-situ, analyzing the impact of various factors including irradiation, temperature and humidity levels of various derivative halides. Morevoer, electrochemical impedance spectroscopy on the corresponding devices was used to link structural changes to electronic events, which can influence cell performance.
In-situ Raman spectroscopy of MAPbI3 perovskite.
[1] Green, M. A., Ho-Baillie, A., Snaith, H. J. The emergence of perovskite solar cells. Nature Photonics 2014, 8(7), 506–514. [2] http://www.nrel.gov/ncpv/, [Online; accessed: 30–January-2015] [3] Bertoluzzi, L., Sanchez, R. S., Liu, L., Lee, J.-W., Mas-Marza, E., Han, H., Bisquert, J. Cooperative kinetics of depolarization in CH3NH3PbI3 perovskite solar cells. Energy & Environmental Science 2015, In press. [4] Noh, J. H., Im, S. H., Heo, J. H., Mandal, T. N., & Seok, S. Il. Chemical management for colorful, efficient, and stable inorganic-organic hybrid nanostructured solar cells. Nano Letters 2013, 13(4), 1764–9. [5] Eperon, G. E., Stranks, S. D., Menelaou, C., Johnston, M. B., Herz, L. M., & Snaith, H. J. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells. Energy & Environmental Science 2014, 7(3), 982. [6] Antoniadou, M., Siranidi, E., Vaenas, N., Kontos, A.G., Stathatos, E., P. Falaras, P. Photovoltaic performance and stability of CH3NH3PbI3−xClx perovskites”, J. Surf. Interf. Mater. 2014, 87, doi:10.1166/jsim.2014.1060.

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