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Metal-halide perovskites form a popular class of materials with intriguing optoelectronic properties. A fundamental understanding of the variations in the energy levels positions, as a function of the materials composition, is missing, however. Researchers from the TU/e and the University of Cologne have developed a new methodology to determine the absolute energy level positions of all primary perovskites, and provide explanations for the variations in these positions.
The materials class of halide perovskites (AMX3, where A is an alkali cation, or an organic cation, such as methylamine (MA) or formamidine (FA); B is lead or tin; X is a halide) has attracted enormous attention in the scientific community recently, due to breakthroughs in perovskite optoelectronics, mainly in photovoltaics and LEDs. By exchanging or mixing different ions in the perovskite crystal, it is possible to tune the optical gap of these semiconductors, allowing for an optimal overlap with the solar spectrum in absorption or a tunable wavelength of emission. The changes in band gaps are well characterized. However, the underlying physical origin of these changes, the shifts in the positions of the valence band maximum (VBM) and the conduction band minimum (CBM), are unknown. Knowing these positions is also crucial for designing contact layers that can inject/extract charge carriers efficiently into/from these perovskites, as is required in optoelectronic devices, or for designing multilayer heterojunction devices with proper band offsets between the layers.
Interplay - Subtle - Factors - Types - Ions
"We were interested to understand the complex interplay of a few subtle yet correlated factors when combining different types of ions in the perovskite crystal structure," explains Shuxia Tao, Assis. Prof. from the Center of Computational Energy Research (CCER) of Applied Physics, TU/e. Together with Selina Olthof, experimental physicist...
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