Lead-Free Cs₂BB′X₆ (B: Ag/Au/Cu, B′: Bi/Sb/Tl, and X: Br/Cl/I) Double Perovskites and Their Potential in Energy Conversion Applications

Abstract

A mere decade-long research focused on perovskites for photovoltaics (PVs) has unearthed their exciting promise. However, as an alternative to the inaugural class of single perovskites, which suffer from instability and toxicity, an interesting class of halide double perovskites (DPs) have recently been in the hot list of photovolatic (PV) researchers. This article presents 27 Cs2BB′X6 halide DPs using different exchange–correlation approximations and reports investigations based on factors such as the Goldschmidt tolerance factor (t) and modified tolerance factor (t ′) and thermodynamical investigations considering mixed decomposition pathways for assessing their stability. The spin–orbit coupling (SOC) is explored to understand the role of the heavy element as an alternative to Pb. A wide range of band gaps (0.2 eV to 2.35 eV) are noticed for the 27 DPs. As a single exception, a halide DP with a trivalent thallium cation exhibits metallic characteristics. Further, an insight into the mechanism behind band gap variation is correlated with different B/B′/X combinations and understood from molecular orbital alignment analysis. Such a broad band gap spectrum has the potential to provide the possibility of integrating them in single- or multiple-junction solar cells or thermoelectric applications. This article, on the whole, hopefully provides insights into the potential of DPs for various applications befitting their particular material properties.

Theoretical Insights on Pb‐Free Rhombohedral CsGeI3 over Cubic CsMX3 (M‐: Pb, Sn, Ge, and X‐: Cl, Br, I) Perovskite‐Based Single‐Junction Solar Cell with Efficiency >30%

“…It is however needed to note that jTB‐mBJ and TB‐mBJ semilocal XC potentials predicted accurate for halide perovskites beyond single‐cation class, that is,vacancy‐ordered A 2 SnX 6 double cation perovskites and some of cation‐ordered Cs 2 BB’X 6 (B‐: Ag, Au, Cu; B’‐: Bi, Sb, Tl; X‐: Cl, Br, I) double‐cation perovskites, respectively. [ 22,29,30 ] In present work, this jTB‐mBJ XC potential has predicted nearly agreeable of rhombohedral CsGeI 3 with experimental report (Table 1). The slightly higher …”

“…It is however needed to note that jTB-mBJ and TB-mBJ semilocal XC potentials predicted accurate E g for halide perovskites beyond single-cation class, that is,vacancyordered A 2 SnX 6 double cation perovskites and some of cation-ordered Cs 2 BB'X 6 (B-: Ag, Au, Cu; B'-: Bi, Sb, Tl; X-: Cl, Br, I) double-cation perovskites, respectively. [22,29,30] In present work, this jTB-mBJ XC potential has predicted nearly agreeable E g of rhombohedral CsGeI 3 with experimental report (Table 1). The slightly higher E expt: g of cubic CsPbI 3 (1.73 eV) than some bandgap reports of cubic CsGeI 3 (1.63 eV) is not significant as the bandgap value is prone to minor variations due to many factors, for example, complex high-temperature cubic-phase synthesis of CsGeI 3 .…”

Lead free A2NaInI6 (A = Cs, Rb, K) double perovskites for optoelectronic and thermoelectric applications

“…When the tolerance factor approaches unity, it suggests that cubic crystal structures tend to be stable. Calculating the tolerance factor involves considering the ionic radii of the atoms involved in the process [38]:…”

Recent developments in lead-free bismuth-based halide perovskite nanomaterials for heterogeneous photocatalysis under visible light

“…, Cs 2 AgBiBr 6 or Cs 2 CuBiBr 6 ), which demonstrates a three-dimensional perovskite structure analogous to ABX 3 . 78–81 Besides, all-inorganic BHPs ( e.g. , Cs 3 Bi 2 Br 9 ) with inorganic A-site cations can exhibit improved thermal and chemical stability compared with their organic–inorganic hybrid counterparts ( e.g.…”

“…77 Furthermore, the introduction of another monovalent cation can produce a halide double perovskite with a general formula of A 2 M(I)BiX 6 (e.g., Cs 2 AgBiBr 6 or Cs 2 CuBiBr 6 ), which demonstrates a three-dimensional perovskite structure analogous to ABX 3 . [78][79][80][81] Besides, all-inorganic BHPs (e.g., Cs 3 Bi 2 Br 9 ) with inorganic A-site cations can exhibit improved thermal and chemical stability compared with their organic-inorganic hybrid counterparts (e.g., MA 3 Bi 2 Br 9 ). 82,83…”