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Title – WHY DO BROMIDE PEROVSKITE SOLAR CELLS HAVE A LARGER VOLTAGE LOSS THAN IODIDE ONES?
Speaker – Prof. Gary Hodes, Dept. of Materials and Interfaces, Weizmann Institute of Science
Venue – February 26, 2020 at 4 PM, SSCU Auditorium

Abstract:
To date, the smallest, avoidable loss in open-circuit voltage (under standard solar illumination) for solar cells that use a halide perovskite (HaP) as the photovoltaically active material, is ~70 mV, a very low value. For cells based on pure bromide HaPs, however, the lowest loss is ~300 mV. The reason for this is unproven, although ‘defects’ are suspected but never directly proven. In this presentation, Ultra-high sensitivity surface photovoltage and wavelength-dependent UV photoelectron spectroscopy) measurements, done in collaboration with the Helmholtz Centre Berlin groups of T. Dittrich and T. Unold, and the Chiba Univ., group of H. Ishii, respectively, are combined to show what we view as the most direct detection of different states extending from the conduction band deep into the bandgap in bromide perovskites. Such states are not seen in iodide HaPs. A reason for this difference is suggested based on the different free energies of formation of the iodides and bromides.