Amine Gas‐Induced Reversible Optical Bleaching of Bismuth‐Based Lead‐Free Perovskite Thin Films

Abstract Reversible optical property changes in lead‐free perovskites have recently received great interest due to their potential applications in smart windows, sensors, data encryption, and various on‐demand devices. However, it is challenging to achieve remarkable color changes in their thin films. Here, methylamine gas (CH3NH2, MA0) induced switchable optical bleaching of bismuth (Bi)‐based perovskite films is demonstrated for the first time. By exposure to an MA0 atmosphere, the color of Cs2AgBiBr6 (CABB) films changes from yellow to transparent, and the color of Cs3Bi2I9 (CBI) films changes from dark red to transparent. More interestingly, the underlying reason is found to be the interactions between MA0 and Bi3+ with the formation of an amorphous liquefied transparent intermediate phase, which is different from that of lead‐based perovskite systems. Moreover, the generality of this approach is demonstrated with other amine gases, including ethylamine (C2H5NH2, EA0) and butylamine (CH3(CH2)3NH2, BA0), and another compound, Cs3Sb2I9, by observing a similar reversible optical bleaching phenomenon. The potential for the application of CABB and CBI films in switchable smart windows is investigated. This study provides valuable insights into the interactions between amine gases and lead‐free perovskites, opening up new possibilities for high‐efficiency optoelectronic and stimuli‐responsive applications of these emerging Bi‐based materials.


Fuxiang
Figure S1.Optical images of CABB and CBI films stored at room temperature and normal pressure after treatment with MA 0 gas.

Figure S3 .
Figure S3.MA 0 gas absorption behavior of different halide salts and perovskite powder in CABB (a) and CBI (b) at the first 6 hours of MA 0 exposure.

Figure S5 .
Figure S5.XRD patterns of CsBr (a) and AgBr (b) powders before and after absorbing MA 0 gas molecules.

Figure S7 .
Figure S7.FTIR spectra of CsBr (a) and AgBr (b) powders before and after absorbing MA 0 gas molecules.

Figure S8 .
Figure S8.XRD patterns of CBI and BiI 3 powders after absorbing MA 0 gas molecules.

Figure S9 .
Figure S9.XRD patterns of CsI before and after absorbing MA 0 gas molecules.

Figure S10 .
Figure S10.FTIR spectra of CsI powders before and after absorbing MA 0 gas molecules.

Figure S11 .
Figure S11.Optical images of optical bleaching in CABB film during EA 0 (a) and BA 0 (b) gas treatment.UV-vis absorption spectra of CABB film at different states during EA 0 (c) and BA 0 (d) gas treatment.

Figure S12 .
Figure S12.(a) XRD patterns of CABB film after different amines treatment.(b) The enlarged view of the (220) and (400) diffraction peaks in the XRD patterns.(c) The intensity of (400) diffraction peak in different amine gases treated CABB films.(d) The diffraction intensity ratio between the (400) and (220) peaks in different amine gases treated CABB films.

Figure S13 .
Figure S13.UV-vis absorption spectra of CBI film at different stages during EA 0 (a) and BA 0 (b) gas treatment.

Figure S14 .
Figure S14.(a) Optical images of optical bleaching in Cs 3 Sb 2 I 9 film during MA 0 gas treatment.(b) UV-vis absorption spectra of Cs 3 Sb 2 I 9 film at different states during MA 0 gas treatment.

Figure S16 .
Figure S16.Variation of the transparent to color phase transition time of CBI and CABB film under different temperatures.

Figure S17 .
Figure S17.Optical images of data encryption and decryption process based on CABB film and MA 0 gas.

Figure S18 .
Figure S18.(a) UV-vis absorption spectra of CABB film at transparent (State II) and colored states for repeating 20 cycles.(b)The cycling stability of the absorbance at 437 nm in CABB film.(c) Optical images of CABB film after 1-20 cycles of phase transitions.

Figure S20 .
Figure S20.(a) UV-vis absorption spectra of CBI film at transparent (State II) and colored states for repeating 50 cycles.(b) XRD patterns of CBI film after 1 and 50 cycles of phase transitions.(c) Optical images of CBI film after 1-50 cycles of phase transitions.

Figure S21 .
Figure S21.Optical images of annealed CABB (a) and CBI (b) films after 2 seconds to 40 hours of MA 0 gas exposure.XRD patterns of annealed CABB (c) and CBI (d) film after 2s-40h of MA 0 gas exposure.UV-vis absorption spectra of annealed CABB (e) and CBI (f) film after 2s-40h of MA 0 gas exposure.

Figure S22 .
Figure S22.XRD patterns of CABB (a) and CBI (b) film before and after 180 days surrounding environment storage.