Strain-Induced Band-Edge Modulation in Lead-Free Antimony-Based Double Perovskite for Visible-Light Absorption

Abstract

Herein, we synthesized Sb-based single crystals (SCs) of Cs2AgSbCl6 with an impressive low bandgap of ∼1.82 eV and demonstrated the effect of strain on optical properties. Interestingly, the polycrystalline ground powder and the heated SCs of Cs2AgSbCl6 exhibited a larger bandgap of ∼2.55 eV. The reduction of bandgap is attributed to the existence of strain in the SC as confirmed by X-ray diffraction and Raman spectroscopy and supported by density functional theory (DFT) calculations. The strain engineering for bandgap reduction can play a pivotal role for developing low-bandgap lead-free double perovskite for environmentally friendly solar cell applications.

Lead-free double perovskites: how divalent cations tune the electronic structure for photovoltaic applications

“…The calculated lattice parameter of pristine Cs 2 AgSbCl 6 (a = 10.85 Å) is comparable to the experimental lattice parameter (a = 10.70 Å) and other theoretical calculations (a = 10.83 Å). 11,45,46 In configuration 1, we observed a good correlation of the elongation of the lattice constant with the reported value of the ionic radius of Sn 2+ . 47 Moreover, the contraction of the cell volume is shown for Ge 2+ , Zn 2+ , and Cd 2+ , in good agreement with their ionic radii.…”

Mixed Organic Cations Promote Ambient Light-Induced Formation of Metallic Lead in Lead Halide Perovskite Crystals

“…Instead, it could be attributed to the yellow crystals being structurally compressed, as we reported previously . When we carried out X-ray rocking curve (omega scan) measurements (Figure c) on the as-grown crystals, we obtained a significantly narrowed full-width at half-maximum (FWHM) of 0.014° in the case of the (004) peak for the black crystals, compared to 0.18° for the yellow crystals, indicating that the black ones have a much enhanced crystallinity due to reduced density of dislocations and preferred orientation of crystallites. − This allows excluding color darkening to be a result of induced mid-band gap defects due to the disruption of the crystalline order, as previously reported for Bi-doped MAPbBr 3 single crystals. , LXRPD patterns of both as-grown black crystals and their powders (yellow in color) are identical in terms of peak positions (Figure S6a in the Supporting Information); therefore, we can exclude strain as a cause of the unexpected change in color …”

“…33,39 LXRPD patterns of both as-grown black crystals and their powders (yellow in color) are identical in terms of peak positions (Figure S6a in the Supporting Information); therefore, we can exclude strain as a cause of the unexpected change in color. 34 The higher crystallinity of the black crystals compared to the yellow ones was also reflected in their powders when we carried out SXRPD measurements. We observed that the diffraction peaks in the powder patterns from the black crystals are about 5 times more intense compared to those in the powder patterns from the yellow crystals (Figure S6b).…”

“…Other reported origins for color darkening in metal halide perovskites include the formation of localized mid-band gap states due to the presence of mixed valence cations 30,31 or to the formation of color centers, such as Pb 3+ , 32 and the induced formation of mid-band gap defects related to the disruption of the crystalline order 33 or to strain. 34 In our black crystals, we excluded all these origins through detailed characterization as we describe next. First, our XPS results indicate that the only difference between the black and yellow crystals is the increased Pb(0) in the black crystals as discussed above.…”

Advancing Efficiency and Stability of Lead, Tin, and Lead/Tin Perovskite Solar Cells: Strategies and Perspectives

“…[ 23,26,46–48 ] Another alternative double‐perovskite structure has also been engineered by mixing monovalent (B + ) and trivalent (B 3+ ) cations in place of the divalent metal cation with the general formula A 2 B + B 3+ X 6 . The most explored double perovskites are Cs 2 (Ag,Bi)Br 6 , [ 49 ] Cs 2 AgSbCl 6 , [ 50 ] Cs 2 (Ag,In)Cl 6 , [ 51 ] and MA 2 (Ag,Bi)Br 6 . [ 52,53 ] All of the abovementioned stable alternatives have been used for solar cell devices but device efficiencies have not come close to the more established Pb‐ and Sn‐based ABX 3 perovskites.…”