Mechanisms of mechanochemical synthesis of cesium lead halides: pathways toward stabilization of α-CsPbI3

Abstract

Cesium lead iodide with cubic perovskite structure (a-CsPbI 3 ) is gaining significant interest in photovoltaic applications due to its excellent absorbance of the visible solar light and other attractive optoelectronic properties. However, the synthesis of stable a-CsPbI 3 poses a significant challenge. Mechanochemical synthesis is emerging as a suitable method for the preparation of cesium lead halides. This work investigates the ball milling-induced synthesis of cesium lead halides perovskite phase using halide mixing or doping approaches. The synthesis in the CsI ? PbI 2 , CsBr ? PbBr 2 , CsBr ? PbI 2 , and CsI ? PbI 2 ? NdI 3 mixtures and halide exchange reactions in the CsPbBr 3 ? 3KI and CsBr ? PbBr 2 ? 3KI systems are investigated to elucidate the mechanism of this process. Then, CsPb(I 1-x Br x ) 3 and CsPb( 1-y )Nd y I 3 materials with different x and y ratios are prepared, and their stability is probed in the air using light absorption spectroscopy. These results suggest that Nd doping is more efficient in the stabilization of the perovskite structure than partial replacement of iodine with bromine. Microstructure observations reveal the existence of two different product formation mechanisms depending on the mechanical properties of reactants. The results reveal that the milling temperature has a significant impact on the reaction kinetics. The produced particles nucleate and grow at the reactant interface and retard the synthesis reaction by creating a diffusion barrier. Extended milling reduces the product particle size and creates fresh contact between reactants, thus facilitating reaction completion.

Improving the Stability of α-CsPbI3 Nanocrystals in Extreme Conditions Facilitated by Mn2+ Doping

“…13−16 The small-sized Cs + ions cannot maintain the cubic framework of a corner-sharing PbI 6 4− octahedron, which leads to phase transformation. 1,17,18 To solve this issue, many methods have been used to stabilize α-CsPbI 3 , such as A,-B-, or X-site doping. 11,19−21 It should be noted that B-site doping can improve the crystal-phase stability of CsPbI 3 without any side effects, such as ionic migration, phase separation, or photodecomposition.…”

“…Cubic-phase CsPbI 3 (α-CsPbI 3 , E g = 1.73 eV) having good optoelectronic performance can be easily transformed to an orthorhombic phase (δ-CsPbI 3 , E g = 2.25 eV) with poor optoelectronic properties. − The small-sized Cs + ions cannot maintain the cubic framework of a corner-sharing PbI 6 4– octahedron, which leads to phase transformation. ,, To solve this issue, many methods have been used to stabilize α-CsPbI 3 , such as A,- B-, or X-site doping. ,− It should be noted that B-site doping can improve the crystal-phase stability of CsPbI 3 without any side effects, such as ionic migration, phase separation, or photodecomposition. , Rogach et al. used SrCl 2 as a coprecursor to improve the phase stability of α-CsPbI 3 NC solutions after 60 days.…”

Simple Production of Highly Luminescent Organometal Halide Perovskite Nanocrystals Using Ultrasound-Assisted Bead Milling

“…Further, we clarified the effects of the mass of the beads and milling time because nonoptimized milling conditions often cause the formation of PeNCs with varied shapes and sizes owing to over/less grinding, thus leading to undesirable heterogeneity in the PL frequency. , Because the effects of the mechanochemical conditions is significant, the bead-to-precursor mass ratios systematically varied from 25, 50, and 100 to 200 mass ratios for a processing time ranging between 15 and 40 min (Figure S8). During the ultrasound irradiation with beads, an increase in PLQY as a function of the milling time was confirmed in each condition (Figure a); however, only 11% of PLQY was confirmed in the milling without beads (Table S1) (PLQY values are summarized in Supporting Information Table S4).…”

“…This study strongly proposes that the perovskite crystal structure can be used in the production of environmentally friendly and high output PeNCs, while maintaining their superior PL properties. Therefore, the top-down approach is a suitable way for the large-scale practical production of highly luminescent PeNCs whose applications in various nanomaterials (carbon and metal oxide) have already been demonstrated. , As a low-cost process, ball milling is preferable owing to its simple operation at room temperature and direct synthesis from the bulk powder of the perovskite precursors. − Moreover, it does not require a polar solvent that causes dispersion of the destabilized PeNC owing to the sensitivity of the perovskite to the polar solvent . Thus, milling is an advantageous process for the production of highly luminescent PeNCs on a large scale.…”

Recent Advances and Perspectives on Powder‐Based Halide Perovskite Film Processing

“…Only a few studies have focused on the impact of specific processing parameters like reactant particle sizes on the resulting perovskite, or on the reaction mechanisms. [20,64,65] Further investigations are needed to be able to adjust the powder properties more precisely. It will also be interesting to see, to which extent further passivation concepts are transferable from solventbased processing to mechanochemically synthesized powders, and whether new passivation approaches can be realized, as the addition of passivating compounds is not limited by solubility aspects.…”