Stabilization of Photoactive γ-CsPbI₃ Perovskite Phase by Incorporation of Mg

Abstract

Fully inorganic CsPbI 3 perovskite has been widely explored as an alternative light-harvesting material owing to its superior thermal stability over the organic−inorganic halide perovskite and the suitable band gap. However, stabilization of the photoactive CsPbI 3 phase at room temperature (RT) remains the biggest challenge. The photoactive α-CsPbI 3 which requires high-temperature synthesis (above 320 °C) transforms into the photoactive γ-CsPbI 3 at RT and on exposure to ambient rapidly transforms into the non-photoactive δ-CsPbI 3 . Herein, we investigate the effect of incorporating Mg 2+ in the CsPbI 3 lattice. It has been found that the photoactive γ-phase of CsPbI 3 can be stabilized for more than 167 days at RT in a nitrogen atmosphere by incorporating Mg 2+ inside the lattice. Incorporating Mg 2+ inside the lattice of CsPbI 3 has led to enhanced optoelectronic properties along with enhanced phase and thermal stability.

Revealing the impact of the host-salt non-stoichiometry on the performance of perovskite solar cells

“…We note that accelerated growth of the a-phase is correlated with thermodynamically lower phase transition energies owing to the smaller ionic radii of the MA + -cation, which result in enhanced nucleation. [49][50][51][52] Thus, the major advantage arises from the incorporation of the smaller host salt, while the inclusion of larger cations is found to retard the nucleation. 19 The crystallization rate, crystal size and lm morphology of the distinct perovskite lms are inuenced by the MAI concentration and how this excess salt is driven out of the lm.…”

“…We note that accelerated growth of the α-phase is correlated with thermodynamically lower phase transition energies owing to the smaller ionic radii of the MA + -cation, which result in enhanced nucleation. 49–52 Thus, the major advantage arises from the incorporation of the smaller host salt, while the inclusion of larger cations is found to retard the nucleation. 19…”

The Compound Effect of Mg and Tris(2-aminoethyl)amine for Long-Term Phase Stability in the γ-CsPbI3 Perovskite Film

“…In our recent work, it has been extensively studied that the inclusion of Mg in CsPbI 3 results in the formation of γ-phase at much lower temperatures ranging from 80 to 120 °C as compared to the CsPbI 3 film formed above 320 °C. We have observed that there is a drastic enhancement in the thermal stability as well as phase stability in the Mg-containing film as compared to the pristine CsPbI 3 film . However, the ambient stability still remains a critical issue.…”

“…It has been extensively reported that thermodynamically, the most stable phase is the γ-phase among the three photoactive phases. When the α-CsPbI 3 formed at temperatures above 320 °C is quickly quenched to RT in an N 2 ambient temperature, it transforms to γ-CsPbI 3 , which is a metastable phase. , However, if α-CsPbI 3 is allowed to cool slowly or if exposed to humidity, it transforms directly to the δ-phase. , …”

“…Another approach that has been identified to stabilize the photoactive phase of CsPbI 3 is by partial substitution of the B site occupied by Pb 2+ with some smaller radius elements such as Ca 2+ , Mn 2+ , Ge 2+ , Cu 2+ , Eu 2+ , Bi 3+ , , Sn 2+ , Zn 2+ , Mg 2+ , and Sr 2+ , or by partial substitution of the X site occupied by I – with some smaller radii halide like Br – − and Cl – In addition to tuning the tolerance factor, other effective ways of stabilizing the photoactive phase of CsPbI 3 is by reducing the crystallite size in the nanometer range and introducing strain. ,− …”