Integrated Experimental and Theoretical Approach for Efficient Design and Synthesis of Gold-Based Double Halide Perovskites

Abstract

Applied cutting-edge electronic structure and phonon simulations provide a reliable knowledge about the stability of perovskite structures and their electronic properties, which are crucial for design of effective nanomaterials. Gold is one of the exceptional elements, which can exist both as a monovalent and a trivalent ion in the B site of a double perovskite such as A2BIBIIIX6. However, until now, electronic properties of Cs2AuIAuIIIX6 have not been sufficiently explored and this material was never synthesized using Au1+ and Au3+ precursors in the preparation route. Here, computational simulations combined with an experimental study provide new insight into the properties and synthesis route of Cs2AuIAuIIIX6 (X = Cl, Br, and I) perovskites. First-principles calculations reveal that tetragonal Cs2AuIAuIIIX6 (X = I, Br, Cl) molecules present a band gap of 1.10, 1.15, and 1.40 eV, respectively. Application of novel approaches in the simulations of the VB-XPS for Cs2AuIAuIIICl6 allows replication of the observed spectrum and provides strong evidence of the reliability of the obtained results for the other perovskites Cs2AuIAuIIIX6, X = Br, I. Following theoretical findings, a one-step preparation route of the Cs2AuIAuIIICl6 is developed using a combination of monovalent and trivalent gold precursors at a relatively low temperature. It should be emphasized that this is the first synthesis of this material at low temperatures, allowing for obtaining highly crystalline Cs2Au2Cl6 particles with controlled morphology and without gold impurities. The band gap of synthesized Cs2AuIAuIIICl6 is extended into the NIR spectral range, where most other double perovskites are limited to higher energies, limiting their usage in single junction solar cells or in photocatalysis. The as-synthesized Cs2AuIAuIIICl6 exhibits high efficiency in a photocatalytic toluene degradation reaction under visible light irradiation. The developed approach provides information necessary for structure manipulation at the early stage of its synthesis and offers a new and useful guidance for design of novel improved lead-free inorganic halide perovskite with interesting optical and photocatalytic properties.

A New Perspective and Design Principle for Halide Perovskites: Ionic Octahedron Network (ION)

“…Figure b shows systematic red shifting of the absorption across theses crystals and indicates bandgap narrowing with an increasing amount of reduced Au­(I). The results confirm that introduction of the Au­(I) dopants would reduce the absorption bandgap of the Cs 8 Au 3.5 In 1.5 Cl 23 new halide perovskites from 2.37 to 1.43 eV, a value that is quite comparable with that of Cs 2 Au­(I)­Au­(III)­Cl 6 . The Au­(I) dopant concentration produced with different molar ratios of AA can be estimated from the decrease in intensity of the characteristic absorption peak of [AuCl 4 ] − at 313 nm .…”

“…The results confirm that introduction of the Au(I) dopants would reduce the absorption bandgap of the Cs 8 Au 3.5 In 1.5 Cl 23 new halide perovskites from 2.37 to 1.43 eV, a value that is quite comparable with that of Cs 2 Au(I)-Au(III)Cl 6 . 31 The Au(I) dopant concentration produced with different molar ratios of AA can be estimated from the decrease in intensity of the characteristic absorption peak of [AuCl 4 ] − at 313 nm. 32 This analysis suggests that less than 3% of the [AuCl 4 ] − will be reduced with AA when the molar ratio of AA is less than 5% (Figure S9).…”

Facile strategy to synthesize cesium gold-based bromide perovskites: an integrated experimental and theoretical approach to study temperature-dependent structural and optical properties

“…S3, ESI †), as seen in the case of Cs 2 Au 2 Cl 6 perovskites. 19 This indicates the evolution of different structures of CsAuBr 3 /CsAuBr 4 to the stable Cs 2 Au 2 Br 6 phase at 220 1C. The morphological studies for CsAuBr 4 /CsAuBr 3 /Cs 2 Au 2 Br 6 were not performed beyond 220 1C as the compounds started degrading due to the formation of CsBr and Au impurities at higher temperatures (Fig.…”

“…2,[8][9][10]16 In this study, we wish to demonstrate that indeed CsAuBr 3 /CsAuBr 4 phases are metastable, and the ultimate stable phase is Cs 2 Au 2 X 6 which is also the compound of optical interest at present. 5,7,[17][18][19] The effect of ambient conditions (heat, oxygen, and humidity) is essential to be established in the light of their varied phase relations.…”

Gold-Based Double Perovskite-Related Polymorphs: Low Dimensional with an Ultranarrow Bandgap

“…Notably, to the best of our knowledge, HeptDA also holds the lowest bandgap for any known halide perovskite compounds, such as Cs 2 AgTlBr 6 (0.95 eV), 54 Cs 4 CuSb 2 Cl 12 (1.02 eV), 55 and Cs 2 AuAuI 6 (1.1 eV). 51 Thus, such a material exhibits potential in photodetectors for near-to middle-infrared (900 nm to 3 μm) radiation. 56 To understand the electronic structure of these Au-based polymorphs and the reason behind their ultralow bandgaps, we calculated the band structure and the PDOS using the PBE functional with SOC using the VASP.…”