(CH₃NH₃)AuX₄⋅H₂O (X=Cl, Br) and (CH₃NH₃)AuCl₄: Low‐Band Gap Lead‐Free Layered Gold Halide Perovskite Materials

Abstract

Perovskites olar cells have recently enabledp ower conversion efficiencyc omparable to established technologies such as silicon and cadmiumt elluride.O ngoing efforts to improve the stability of halide perovskites in ambient air has yielded promising results. However,t he presence of toxic heavy elementl ead (Pb) remains am ajor concern requiring further attention. Herein, we report three new Pbfree hybrido rganic-inorganic perovskite-typeh alides based on gold (Au), (CH 3 NH 3 )AuBr 4 ·H 2 O( 1), (CH 3 NH 3 )AuCl 4 ·H 2 O( 2), and (CH 3 NH 3 )AuCl 4 (3). Hydrated compounds 1 and 2 crystallize in ab rand-new structure type featuring perovskite-derived 2D layers and 1D chains based on pseudo-octahedral AuX 6 building blocks. In contrast,t he novel crystal structure of the solvent-freec ompound 3 shows an exotic non-perovskite quasi-2D layered structure containing edge-and corner-shared AuCl 6 octahedra. The use of Au metal instead of Pb resultsi nu nprecedented low band gaps below 2.5 eV for single-layered metal chlorides and bromides. Moreover, at room temperature the three compounds show aw eak blue emission due to the electronic transition between Au-6s and Au-5d, in agreement with the density function theory (DFT) calculation results. These findings are discussed in the context of viability of Au-based halidesa sa lternatives for Pb-based halides for optoelectronic applications.

Anion⋅⋅⋅Anion Coinage Bonds: The Case of Tetrachloridoaurate

“…À [42] and Au(CN) 4 À [43] (Tables S15 and S16). In conclusion, experimental evidence is given that the gold atom of AuCl 4 À anions form short contacts with both neutral and anionic nucleophiles in the solid state.…”

Anion⋅⋅⋅Anion Coinage Bonds: The Case of Tetrachloridoaurate

“…The experimental and theoretical results reported here prove that anion ⋅⋅⋅ anion interactions involving AuCl 4 − are reliable and robust supramolecular synthons that consistently control the interactions in crystalline structures. The use of these interactions in the design and control of structural features of materials may allow a fine‐tuning of their functional properties, for example, in perovskites for solar cells [42] or ambient pressure superconductors [39] that contain AuCl 4 − anions. Analogous interactions occurring in solution may account for the Lewis acid catalytic activity of the tetrachloroaurate anion [48] .…”

Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview

“…As for the lead-based, lead-free perovskites can also be divided to organic–inorganic and all-inorganic. For organic–inorganic lead-free perovskites, standard methylammonium [39,40,50], butylamine [32], 1,3-propanediammonium [51], and phenethylammonium [52] can be used as the A cations. For all-inorganic lead-free perovskites, the most used A cation is Cs, however there are several reports on Rb and Rb/Cs mixture [29,37].…”

“…The perovskite film exhibited pronounced sensitivity to deep UV and UV light illumination with response rise/fall time speeds of 26.2/49.9 ms. Another chemical element that can be used for substitution of lead atom is gold. Two new hybrid organic–inorganic gold perovskite-like halides, (CH 3 NH 3 )AuX 4 ⋅H 2 O (X = Br and Cl) were reported in work [50]. Non-stoichiometric 2:1 molar ratio of methylammonium halides (MACl or MABr) and Au (III) halides (AuBr 3 or AuCl 3 ) in water/methanol 0.2 M solution system was used.…”

“…The analysis of literature shows that lead-free perovskites can be formed as films [32,39,40,44,48,56,57], single crystals [25,26,29,32,33,41,42,44,45,46,47,50], and NCs [32,38,40,48,49]. The synthetic methods are similar to that used for lead-based perovskites.…”