Controlled Synthesis of High-Quality Oriented 2D Chiral Perovskites Thin Films

Chiral 2D perovskites have emerged as promising materials for circularly polarized photoluminescence (CPL), polarized light detectors, and spintronic applications.^1,2 The intercalation of chiral molecules into these 2D layered structures causes changes in the crystalline structure of the inorganic sublattice such that causes it to adopt a chiral crystalline symmetry. More specifically, the material loses the inversion center of symmetry and mirror reflections, generating different absorption cross sections for right- as compared to left-circularly polarized light. While the lamellar (2D) phases are of primary interest in optoelectronic applications, the thermodynamically more stable 1D phases often forms during the synthesis and processing of these semiconductors.³ For instance, when growing single-crystals of (MBA)₂PbI₄ (MBA = R- or S-α-methylbenzylammonium), the cooling rate is critical to guarantee phase-purity of the desired 2D material. During processing, annealing above 80° C will induce the formation of the 1D phase, possibly via thermal decomposition. Most reports in the literature use N,N-dimethylformamide (DMF) as the solvent for the fabrication of thin films, which require high-temperature annealing and thus causes invariable formation of the 1D phase. In this work, we developed a simple fabrication method for phase-pure 2D perovskites thin films using acetonitrile solutions and milder annealing temperature. In-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) was used to follow the transformation from reagents to products resulting in highly oriented thin films. GIWAXS and circular dichroism measurements demonstrate that the use of these solvents with subsequent annealing at 65° C leads to a highly oriented, phase-pure 2D phase suitable for optoelectronic applications.

References

[1] Kim, Y.-H. et al. Chiral-induced spin selectivity enables a room-temperature spin light-emitting diode. Science (1979) 371, 1129–1133 (2021).
[2] Ahn, J. et al. A new class of chiral semiconductors: chiral-organic-molecule-incorporating organic–inorganic hybrid perovskites. Mater Horiz 4, 851–856 (2017).
[3] Scalon, L. et al. Tuning Phase Purity in Chiral 2D Perovskites. Adv Opt Mater 12, (2024)