| AVS 64th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology Division | Wednesday Sessions |
| Session NS+SS+SU-WeM |
| Session: | Nanotechnology for Renewable Energy |
| Presenter: | David Cahen, Weizmann Institute of Science, Israel |
| Correspondent: | Click to Email |
Ferroelectricity, well-known in oxide perovskites, was suggested as possible reason for the outstanding solar-to-electrical energy conversion of MAPbI3 & MAPbBr3-based halide perovskite PV cells, esp. because ferroelectric domain wall conduction was thought to keep photogenerated charges separated.( à low carrier recombination rate à high photovoltage efficiency).
Contradicting e xperimental evidence, relevant to ferroelectricity, is based on structural diffraction, electric field vs. polarization plots, second harmonic generation and piezoelectricity measurements . To resolve this debate we first asked if
· the materials are pyroelectric, direct evidence for spontaneous polarization, a necessary condition for ferroelectricity.
· polar-domains exist in the structure, as often found in many ferroelectric materials.
Using home-grown, well-characterized single crystals, we find the cubic phases of MAPbI3 (>330K) and MAPbBr3 (>236K) phase to be non-polar, excluding ferroelectricity in them. The tetragonal phase of MAPbI3, however, shows clear evidence of pyroelectricity when probing the potentially-polar, [001], crystallographic orientation, proving its polar nature. By adding low-temperature electric field vs. polarization and room temperature SHG studies and optical observations of polar domains, we arrive at a clear-cut conclusion that MAPbI3 is ferroelectric in the tetragonal phase. I will briefly dwell on the remaining question, i.e., “does that really matter?”.
* work done by Yevgeny Rakita, Dr . David Ehre, Omri Bar-Eli, Elena Meirzadeh, Hadar Kaslasi, Yagel Peleg, with Profs. Gary Hodes, Igor Lubomirsky, Dan Oron, all from the Weizmann Inst.