Optical and Structural Property Tuning in Physical Vapor Deposited Bismuth Halides Cs₃Bi₂(I_1–xBr_x)₉ (0 ≤ x ≤ 1)

Abstract

Crystalline films of lead-free all-inorganic Cs 3 Bi 2 X 9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs 3 Bi 2 (I 1– x Br x ) 9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs 3 Bi 2 I 9 to 2.64 eV for Cs 3 Bi 2 Br 9 . X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts.

In Situ Growth of Cs3Bi2Br9 Quantum Dots on Bi-MOF Nanosheets via Cosharing Bismuth Atoms for CO2 Capture and Photocatalytic Reduction

“…Moreover, Cs 3 Bi 2 Br 9 was reported to show outstanding performance for the selective conversion of CO 2 to CO by effectively reducing the reaction energy of the rate-limiting step of *CO 2 to *COOH intermediates . In particular, the Cs 3 Bi 2 Br 9 perovskite quantum dot (PQD) was proposed to be an ideal material for CO 2 conversion, which benefited from its intriguing quantum confinement effect, small size effect, and photoelectric efficiency. − Unfortunately, the strong aggregation tendency limits their long-term stability.…”

Band Gap Tuning Through Cation and Halide Alloying in Mechanochemical Synthesized Cs3(Sb1-xBix)2Br9 and Cs3Sb2(I1-xBrx)9 Solid Solutions

“…Indeed, the Raman spectrum of the Cs3Bi2Br9 sample clearly shows the characteristic modes at 165 and 190 cm -1 , due to the bond vibrations inside the octahedral cage, BiBr6, as already described in our previous work. 36 In analogy with the isomorphic Cs3Bi2Br9, also for Cs3Sb2Br9 the Raman response qualitatively presents the same spectral fingerprints: a broadened structure centered at about 70 cm -1 clearly resulting from the overlapping of different modes and two sharp and symmetric modes peaked at 182 and 210 cm -1 , resulting from the Sb-Br bond vibrations in the octahedral unit SbBr6. The proper assignment of the mode symmetry seems to be controversial.…”

“…The values of direct and indirect band gaps for Cs3Sb2Br9 and Cs3Bi2Br9 are in agreement with those previously reported in the current literature. 34,36,39,51 By looking at Figure 5b, a significant bowing of the band gap for mixed compositions is observed. This result is unexpected since, in general, metal ion replacement in solid solution provides a scaling of the band gap obeying the Vegard's law.…”

“…It is of relevance to report here this novel tuning strategy for defective perovskites which allows to achieve significant lower band gap values through metal alloying instead of the usual halide mixing which is known to be the main strategy to modulate the absorption edge in these systems. 25,26,36 Cs3Sb2(Br1-xIx)9 System…”

“…Among these systems, bismuth-and antimony-based perovskite derivatives of general formula Cs3M2X9 (M=Bi, Sb; X=Br, I) have shown a strong technological potential in particular in the area of photocatalysis (both for solar fuel generation and organic synthesis) and photodetection. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Bismuth-based defect-ordered perovskites have been object of more intense studies with respect to the corresponding Sb systems, notwithstanding their appealing optoelectronic properties such as high carrier mobility, low trap density, and long diffusion length. As a matter of fact, Cs3Sb2Br9 millimeter-sized single crystals and nanoflakes have been applied in the fabrication of photodetectors with excellent performance in terms of responsivity and detectvity.…”