Low-Dimensional Hybrid Lead Iodide Perovskites Single Crystals via Bifunctional Amino Acid Cross-Linkage: Structural Diversity and Properties Controllability

Abstract

Three-dimensional perovskite AMX3 has great potential in photoelectric applications, but the poor stability is a major problem that restricts its practical application. The emergence of lower dimensional perovskite solves this problem. Here, we have synthesized a group of novel low-dimensional perovskites with diverse structures. Different amino acids were incorporated in the perovskite cage. The formulas of the compounds are (A′) m PbI m+2 (A′ = COOH­(CH2) n NH2, n = 1, 3, 5, 7, 9). These families of materials demonstrate structure-related stability, tunable bandgap, and different photoluminescence. Single-crystal X-ray diffraction indicated that the five materials employ different structure types varying from edge-sharing structures to face- and corner-sharing Pb/I structures by adjusting the number of C atoms in organic cations, and the level of [PbI6]4– octahedral distortion was also identified. The film prepared using these materials with longer carbon chains (n = 5, 7, 9) showed better stability, and they did not decompose within one year at 75% RH, 40 °C. The bifunctional organic ions containing carboxyl groups as spacer cations will form additional hydrogen bonding between perovskite layers, resulting in higher stability of the material. The band gaps of these materials vary from 2.19 to 2.6 eV depending on the octahedral connection mode and [PbI6]4– octahedral distortion level, density functional theory calculations (DFT) are consistent with our experimental trends and suggest that the face-sharing structure has the maximum band gap due to its flatter electron band structure. Bright green fluorescence was observed in (COOH­(CH2)7NH3)2PbI4 and (COOH­(CH2)9NH3)2PbI4 when excited by 365 nm UV light. A thorough comprehension of the structure–property relationships is of great significance for further practical applications of perovskites.

Exciton–phonon coupling in alanine-based hybrid lead bromide

“…In addition, these values are closer to those previously reported by compounds that show similar effects, as reported by G. Xie et al, who observed a broader PL in compounds with high octahedral distortions 63 . Thus, this wide band found in the emission spectrum of AlaPbBr3.H2O seems related to forming self-trapped states induced by high octahedral distortion levels.…”

“…The relation between bandgap width and octahedra connectivity in halide perovskites was reported in previous works based on bromides and iodides 37 , 36 , 87 , 63 . Such studies present a direct proportionality between the octahedra connectivity and the bandgap as a trend, in the following order: corner-sharing < edge-sharing < face-sharing.…”

“…Since octahedra distortions play fundamental in the optical properties of this kind of compound, it is important to evaluate the degrees of the individual c octahedral distortion in AlaPbBr3.H2O. Thus, we calculated the bond length quadratic elongation (〈𝜆〉), and the bond angle variance (𝜎 2 ) 63,85,89,90 which are given by the equations ( 1) and ( 2) where 𝑑 𝑖 is the Pb-Br bond length, 𝑑 0 is the average length, and 𝛼 𝑖 the angle formed by the Br-Pb-Br, as shown in Figure 2(d). These bond lengths and angles values referring to the [PbBr6] 4-octahedron are given in Table S4; from those we obtained 〈𝜆〉=0.9602 and 𝜎 2 =15.63 deg, respectively.…”

“…59,60 Noticeably, the presence of functional chemical groups with a polar protonrich donating 53,60 capable of forming multiple hydrogen bonds 61 , and establishing strong Coulombic interaction with inorganic moiety gettering all the hybrid-structure stable is of utmost desired. 62 For instance, Xie et al 63 (A′ = COOH(CH2)nNH3, n = 1, 3, 5, 7, 9). They demonstrate the ability of bifunctional organic cations of amino acids to influence the structures of low dimensional perovskites, finding diversity in the connectivity modes of the [PbI6] 4− octahedral, with an edge-, face-, and cornersharing structure.…”

Mixed Halide Ordering as a Tool for the Stabilization of Ruddlesden–Popper Structures

“…Pb–X–Pb bond angle dependence on the organic cation penetration for literature-reported pure halide perovskites (blue dots). − The data for ( t -BA) 2 PbBr 2 I 2 is represented by a red dot. Dashed lines are only guidelines for the eye.…”