Texture Formation in Polycrystalline Thin Films of All‐Inorganic Lead Halide Perovskite

Abstract

Controlling grain orientations within polycrystalline all‐inorganic halide perovskite solar cells can help increase conversion efficiencies toward their thermodynamic limits; however, the forces governing texture formation are ambiguous. Using synchrotron X‐ray diffraction, mesostructure formation within polycrystalline CsPbI2.85Br0.15 powders as they cool from a high‐temperature cubic perovskite (α‐phase) is reported. Tetragonal distortions (β‐phase) trigger preferential crystallographic alignment within polycrystalline ensembles, a feature that is suggested here to be coordinated across multiple neighboring grains via interfacial forces that select for certain lattice distortions over others. External anisotropy is then imposed on polycrystalline thin films of orthorhombic (γ‐phase) CsPbI3‐xBrx perovskite via substrate clamping, revealing two fundamental uniaxial texture formations; i) I‐rich films possess orthorhombic‐like texture (<100> out‐of‐plane; <010> and <001> in‐plane), while ii) Br‐rich films form tetragonal‐like texture (<110> out‐of‐plane; <110> and <001> in‐plane). In contrast to relatively uninfluential factors like the choice of substrate, film thickness, and annealing temperature, Br incorporation modifies the γ‐CsPbI3−xBrx crystal structure by reducing the orthorhombic lattice distortion (making it more tetragonal‐like) and governs the formation of the different, energetically favored textures within polycrystalline thin films.

Impact of Amine Additives on Perovskite Precursor Aging: A Case Study of Light-Emitting Diodes

“…One possible explanation is that FABF and DMA cations together induce a shift in the crystal lattice symmetry and thus lead to a variation in the bandgap. Similar observations can be found in recent work on perovskite photovoltaics where DMAI is used to stabilize β-CsPbI 3 at room temperature with a reduced bandgap. − We thus complete GIWAXS to characterize the crystal structure of FABF/MAI films with optimized DMAI addition ( x = 0.4). We show the integrated X-ray scattering intensity profiles with q values ranging from 0.9 to 1.55 Å in Figure b and two-dimensional (2D) GIWAXS patterns in panels c and d of Figure .…”

Trojans That Flip the Black Phase: Impurity-Driven Stabilization and Spontaneous Strain Suppression in γ-CsPbI3 Perovskite

“…In these instances, additives were intentionally incorporated into the spin coating solution to shift the crystallization dynamics, improving crystallinity and ultimately improving the perovskite crystal symmetry and stability. 50 Using data taken from Steele et al 30 and Vigil et al, 49 Figure 4 B and C resolve the intermediate restructuring in compositions spanning CsPbI 3−x Br x and FA x Cs 1−x PbI 3 , respectively. In both cases, the compositional trend in spontaneous strain suppression roughly follows the same path as heating CsPbI 3 perovskite toward a thermodynamically stable cubic structure (Figure 3A); first is the suppression of ϵ orth , and then, for the case of FA x Cs 1−x PbI 3 , there is a range where a tetragonal system exists before ϵ tet also falls to zero.…”

Implementing Dopant-Free Hole-Transporting Layers and Metal-Incorporated CsPbI2Br for Stable All-Inorganic Perovskite Solar Cells

“…Like the stabilizing effect of heating CsPbI 2 Br toward a stable cubic perovskite structure, we suggest that the doping stabilizes the system because of a reversal of the spontaneous strains leading to phase decay. In addition, this effect is the largest for the Eu system, which we find is the most stable when used in an ambient-stable device . Furthermore, we have recorded focused ion beam (FIB) cross-sectional images of the fabricated devices using the CsPbI 2 Br-based absorbers (Figure S26).…”

“…In addition, this effect is the largest for the Eu system, which we find is the most stable when used in an ambient-stable device. 70 Furthermore, we have recorded focused ion beam (FIB) cross-sectional images of the fabricated devices using the CsPbI 2 Br-based absorbers (Figure S26). To study degradation, we have obtained FIB images of the fresh devices (∼10 h after fabrication) and after 14 days of aging.…”