Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Halide perovskites (mainly methylammonium lead iodide (MAPbI3) and its bromide analog, MAPbBr3) are the next wave of light-harvesting materials for solar cell applications, with the best cells showing certified solar to electrical energy conversion efficiencies over 22 %. The origin for such outstanding performance intrigues the scientific community for the last couple of years. Ferroelectricity has repeatedly been suggested as a possible reason for some of the outstanding properties, especially the low carrier recombination rate and high voltage efficiency. Classical measurements to (dis)prove ferroelectricity require high electric fields, which may give rise to experimental artifacts for these materials, because of possible ion migration and the materials’ low formation energies.1 Since a necessary condition for a material to be ferroelectric is that it will have a non-centrosymmetric and polar nature (point group), we examine these two prerequisite conditions via careful Second-Harmonic-Generation (SHG) polarmapping and pyroelectricity characterization (using the Chynoweth method2). These two experimental methods are more accurate than X-ray- or neutron- diffraction methods, which are limited in explicitly determining small deviations in (non-)centrosymmetric structures.
After reporting3 a clear conclusion on the non-ferroelectric nature of MAPbBr3 (which will be presented as well), we continue our investigation on MAPbI3 and will report our most recent results on it (which, so far, does show some differences with MAPbBr3 ).
1) Fan, Z. et al.; J. Phys. Chem. Lett. 6, 1155–1161 (2015)
2) Lubomirsky, I. & Stafsudd, O. ; Rev. Sci. Instrum. 83, 051101 (2012)
3) Rakita, Y. et al. ;APL Mat. 4, 051101 (2016)
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