Electronic Band Engineering via MI₃ (M = Sb, Bi) Doping Remarkably Enhances the Air Stability of Perovskite CsSnI₃

Abstract

CsSnI 3 is a representative all-inorganic and less toxic perovskite material. However, extreme structural and chemical instability of perovskite CsSnI 3 makes its optoelectronic applications highly challenging. Upon exposure to air and moisture, it immediately undergoes a phase transition to a thermodynamically more stable, but optoelectronically inactive, one-dimensional polymorph near ambient temperature and ultimately deforms into Cs 2 SnI 6 . To prohibit this undesirable process, perovskite CsSnI 3 has to be stored and treated restrictively in an inert atmosphere and encapsulated hermitically. Here, we demonstrate an unusual strategy to markedly enhance the air stability of perovskite CsSnI 3 . Namely, MI 3 (M = Sb, Bi) doping modifies the electronic band structure of perovskite CsSnI 3 . As a result, it is remarkable that its heat of formation reduces, being lower than that of its competing polymorph. Accordingly, otherwise thermodynamically unfavorable perovskite CsSnI 3 becomes more stable than the latter energetically, thereby preventing the undesirable phase transition. SbI 3 (3 mol %)-doped CsSnI 3 retains 96% of its perovskite structure, whereas pristine CsSnI 3 retains only 12% after 12 h of exposure to air with 45−55% relative humidity. MI 3 doping also reduces the energy band gap of perovskite CsSnI 3 . We employed first-principles density functional theory calculations to explain the origin of the enhanced stability and redshifted band gaps. Our current work demonstrates that electronic band structure engineering by chemical doping can be an effective means of controlling the phase stability of polymorphs, which are otherwise difficult to stabilize or unattainable. This strategy can be widely applied to materials with low stability but high technological importance.

The Influence of Spontaneous Oxidative Conversion on the Characteristics of Lead‐Free Halide Perovskite CsSn(IxBr1−x)3 and on the Performance of Perovskite Light‐Emitting Diodes

“…As the air exposure time was prolonged, the intensity of new peaks corresponding to the (111), (002), (222), and (004) lattice planes of Cs 2 SnI 6 increased. [ 27–29,31 ] A peak corresponding to the (011) lattice plane of CsI was also observed, confirming the decomposition and oxidation mechanisms as reported previously. [ 27,28,32–35 ] It was reported that there are two chemical reactions involved: CsSnI 3 → CsI + SnI 2 and 2CsI + 2SnI 2 + O 2 → Cs 2 SnI 6 + SnO 2 .…”

“…After 24 h, the absorption spectrum was almost the same with a hump around 680 nm, which can be attributed to the presence of Cs 2 SnI 6 . [ 27–29 ] In addition, the presence of Cs 2 SnI 6 was confirmed from the XRD patterns shown in Figure 2c. As the air exposure time was prolonged, the intensity of new peaks corresponding to the (111), (002), (222), and (004) lattice planes of Cs 2 SnI 6 increased.…”

“…The published results indicated that upon exposure to air, lead‐free perovskite materials could undergo a transition to a thermodynamically stable phase. [ 27–30 ] To rule out the possibility of the influence of the indoor light on the properties of the perovskite films, the intrinsic degradation of CsSn(I x Br 1− x ) 3 films in glove box was first investigated. As shown in Figure S3 in the Supporting Information, the PL peak positions of CsSn(I x Br 1− x ) 3 films stored in glove box with and without continuous light illumination are stable.…”

Inorganic CsSnI3 Perovskite Solar Cells: The Progress and Future Prospects

“…In 2016, Jellicoe et al first synthesized CsSnI 3 PQDs via a hot-injection method. [128] However, the as-synthesized CsSnI 3 [124] Copyright 2020, American Chemical Society.…”

“…Figure 9. a) Local atoms structure of MI 3 (M ¼ Sb, Bi) doped B-γ and Y phase CsSnI 3 perovskite based on the DFT results; Calculated electronic band structure and projected density of state (PDOS) of b) SbI 3 -doped and c) BiI 3 -doped B-γ CsSnI 3 perovskite. Reproduced with permission [124]. Copyright 2020, American Chemical Society.…”