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Defect tolerance to intolerance in the vacancy-ordered double perovskite semiconductors Cs2SnI6 and Cs2TeI6

DOI: 10.1021/jacs.6b03207 DOI Help

Authors: Annalise E Maughan (Department of Chemistry, Colorado State University) , Alex M. Ganose (University College London, Diamond Light Source) , Mitchell M. Bordelon (Department of Chemistry, Colorado State University) , Elisa M. Miller (Chemical and Materials Sciences Center, National Renewable Energy Laboratory) , David O. Scanlon (University College London; Diamond Light Source) , James R. Neilson (Department of Chemistry, Colorado State University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: June 2016

Abstract: Vacancy-ordered double perovskites of the general formula, A 2 BX 6 , are a family of per- ovskite derivatives composed of a face-centered lattice of nearly isolated [ BX 6 ] units with A -site cations occupying the cuboctahedral voids. Despite the presence of isolated octahe- dral units, the close-packed iodide lattice provides significant electronic dispersion, such that Cs 2 SnI 6 has recently been explored for applications in photovoltaic devices. To elucidate the structure-property relationships of these materials, we have synthesized the solid solution Cs 2 Sn 1 − x Te x I 6 . However, even though tellurium substitution increases electronic dispersion via closer I − I contact distances, the substitution experimentally yields insulating behavior from a significant decrease in carrier concentration and mobility. Density functional calcu- lations of native defects in Cs 2 SnI 6 reveal that iodine vacancies exhibit a low enthalpy of formation and the defect energy level is a shallow donor to the conduction band, rendering the material tolerant to these defect states. The increased covalency of Te–I bonding renders the formation of iodine vacancy states unfavorable, and is responsible for the reduction in con- ductivity upon Te substitution. Additionally, Cs 2 TeI 6 is intolerant to the formation of these defects, as the defect level occurs deep within the band gap and thus localizes potential mobile charge carriers. In these vacancy-ordered double perovskites, the close-packed lattice of iodine provides significant electronic dispersion, while the interaction of the B - and X -site ions dic- tates the properties as they pertain to electronic structure and defect tolerance. This simplified perspective – based on extensive experimental and theoretical analysis – provides a platform from which to understand structure-property relationships in functional perovskite halides.

Subject Areas: Chemistry, Materials

Facility: Advanced Photon Source

Added On: 04/07/2016 18:07

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