Lead-Free Perovskite Cs₂AgBiX₆ Nanocrystals with a Band Gap Funnel Structure for Photocatalytic CO₂ Reduction under Visible Light

Abstract

Huge potentiality of lead halide perovskite nanocrystals (NCs) can be found in optoelectronic and photocatalytic fields. However, the main bottlenecks in photocatalysis are their toxicity and instability. To shake off these issues, lead-free Cs2AgBiX6 (X = Cl, Cl0.5Br0.5, Br, Br0.5I0.5, I) double perovskite NCs were synthesized by a simple antisolvent recrystallization approach. Moreover, the as-prepared Cs2AgBiX6 materials were systematically studied for photocatalytic CO2 reduction, which costed a total electron consumption of 37.8 μmol g–1 under visible light irradiation (λ ≥ 420 nm, 300 W Xe lamp) within 3 h for Cs2AgBiI6. Our study here provides novel ideas of lead-free perovskites for photocatalytic reduction of CO2.

Potential Application of Perovskite Structure for Water Treatment: Effects of Band Gap, Band Edges, and Lifetime of Charge Carrier for Photocatalysis

“…In halide perovskites, the lifetime was determined by employing time-resolved photoluminescence spectroscopy. The result indicates that the substitution in the X-site decreases the lifetime values of 4.38, 0.73, and 0.86 ns for Cs 2 AgBiCl 6 , Cs 2 AgBi(Br 0.5 I 0.5 ) 6 , and Cs 2 AgBiI 6 nanocrystals, (Wu et al, 2021). Much longer lifetimes have been found in Cs 2 AgBiBr 6 , around 660 ns (Slavney et al, 2016).…”

“…Using ion-exchange reactions under mild solvothermal conditions would be preferable in many cases, wherein the reaction is performed at the lowest possible temperature (below 200 °C) sufficient to accelerate exchange kinetics (Park et al, 2017). Different perovskites by anion exchange reaction (see Figure 4) were mentioned in the literature showing enhanced photocatalytic properties, like CsPbX 3 (X = Cl, Br, I) (Akkerman et al, 2015;Loiudice et al, 2019), Cs 2 AgBiX 6 , (X = Cl or Br) (Creutz et al, 2018), and Cs 2 AgBiX 6 (X = Cl, Cl 0.5 Br 0.5 , Br, Br 0.5 I 0.5 , I) (Wu et al, 2021).…”

Pb-free halide perovskites for solar cells, light-emitting diodes, and photocatalysts

“…For example, the synthesized all-inorganic Pb-free double perovskite Cs 2 AgBiX 6 NCs have their indirect bandgaps decreasing from 2.56 eV when X = Cl to 1.82 eV when X = I. 226 As a result, the Cs 2 AgBiI 6 NCs shows the best photoreduction activity with a CO yield of 18.9 μmol g −1 under visible light irradiation (λ ≥ 420 nm, 300 W Xe lamp) within 3 h. Similarly, the bandgap of the 2D layered perovskite Cs 3 Bi 2 X 9 NCs decreases from 3.08 to 2.01 eV as halide X goes from Cl − to I − . 227 The highest CO yielding speed is 54 μmol⋅g −1 when X = Br 0.5 I 0.5 , compared to the 48 μmol g −1 when X = Cl 0.5 Br 0.5 and 11 μmol g −1 when X = I under visible-light irradiation (λ ≥ 420 nm, 300 W Xe lamp) for 3 h. The suitable band structure, wide light absorption range, large photocurrent, and small impedance of Cs 3 Bi 2 (Br 0.5 I 0.5 ) 9 contribute to its greater activity in gas-solid interface than in the majority of the liquid-phase CO 2 reduction systems.…”

Cs2AgBiBr6 Double Perovskites as Lead‐Free Alternatives for Perovskite Solar Cells?

“…[ 73 ] While this material readily forms the ternary compound Cs 3 Bi 2 I 9 , which has been investigated in the community already and expresses poor optoelectronic and photovoltaic properties, [ 74 ] the quarternary structure of Cs 2 AgBiI 6 can only be stabilized in nanocrystals after complicated anion exchange procedures with methylsilane compounds. [ 75,76 ] A promising procedure to stabilize the iodine perovskite was initially shown by the Mitzi group, where large cations have been implemented in the perovskite structure to form a 2D compound. [ 77 ] Here, (bisaminothyl)bithiophene was implemented to form (AET) 2 AgBiI 8 which shows a drastic change in the bandgap by means of energy reduction (2.0 eV) and nature (transition from indirect to direct) which was then realized by other groups using different spacer cations.…”