Crystal Chemistry of Halide Perovskite Semiconductors
Constantinos Stoumpos a
a Department of Materials Science and Technology, University of Crete, Heraklion, 710 03 Crete, Greece, Greece
Invited Speaker, Constantinos Stoumpos, presentation 033
Publication date: 23rd April 2020

Halide perovskites, AMX3 (A+ = Cs, CH3NH3, HC(NH2)2; M2+ = Ge, Sn, Pb and X- = Cl, Br, I), is an emerging class of high-performance semiconductors which operate in the visible and infrared energy range (1.1-3.0 eV). The remarkable physical properties of the halide perovskites stem from their unique electronic structure, which originates from the characteristic arrangement of the ions in the perovskite structure-type. The electronic structure of the halide perovskites is responsible for the observed high absorption coefficients and charge-carrier mobilities, which are comparable to the venerable III-V semiconductors.

 A major challenge in halide perovskites relates to the limited perovskite structure formability due to the strict limitations imposed by the tolerance factor (t) which necessitates the halide perovskites to form only when Cs, CH3NH3 or HC(NH2)2 cations are used as templating A+ cations. These restrictions significantly impact the synthetic toolbox for designing new materials with desired target properties. Thus, exploring new synthetic directions that can modify the crystal structure within the perovskite structure limits presents itself as a great challenge in the field. Using small organic cations that can potentially stabilize the perovskite structure, a wide variety of perovskite-related structures can be obtained. Interesting compounds such as perovskite polytypes or unusual metal halide frameworks (so-called “perovskitoids”) and unconventional dimensionally reduced perovskites. The thus obtained compounds are amenable to property tuning governed by specific structural features as these emerge from the three-dimensional connectivity of the octahedral [MX3]- building blocks. Understanding and controlling these structural features in a designed manner will open the way for the discovery of novel perovskite-based semiconductors which may serve as potent substitutes for the currently employed halide perovskite materials.

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