Spacer Cation Alloying Enables Markedly Improved Chiroptical Properties of Two‐Dimensional Chiral Hybrid Perovskite Nanosheets

Abstract

into their structure-property relationships. [2] The factors of spacer cations (e.g., structure of anchoring group and chain length) are of key importance in advancing the quality and use of 2D halide perovskites for applications in many optoelectronic fields. [2d,3] Concretely, it is necessary to design the structure of the head amino anchoring group with an appropriate size that matches the inorganic layer pockets. [4] For instance, primary ammonium spacer cations are easier to penetrate into the inorganic layer pockets, whilst secondary, tertiary, and quaternary ammonium cation anchoring groups with stronger steric hindrance may lead to greater octahedral lattice distortions and differences in the emission wavelength. [5] Moreover, if bulky groups (e.g., benzyl group) are attached to the amino anchoring site, the 2D perovskite structure may be easily destabilized. [6] On the other hand, spacer cations with suitable chain lengths could provide great bending flexibility of anchoring groups for defects passivation, thereby improving emission intensity and quantum efficiency. [2d] Apart from single spacer cations, organic cations alloying could also be a powerful tool to tune the structural features of perovskites, where the introduction of an additional cation with proper binding energy facilitates the defects passivation and thus promotes the long-term stability of surface cations. [2a,7] Clearly, the spacer cations serving as essential building blocks play a vital role in stabilizing 2D perovskite materials and enabling tunable electronic structures. More promisingly, the incorporation of spacer cations with extra functionality can further expand the application in other areas.Recently, the remarkable combination of valuable characteristics of 2D metal halide perovskites and unique features of chirality motivates intensive exploration of emerging chiral 2D halide perovskite-based materials in circularly polarized luminescence (CPL) photodetectors, circularly polarized lightemitting diodes (LEDs), and spintronic applications. [8] 2D chiral perovskites can be conveniently crafted via utilizing chiral organic spacer cations, which introduce chirality to the system. [9] In addition to the promising optoelectronic properties (e.g., tunable band gap, strong quantum confinementThe combination of unique features of chirality and promising attributes of 2D halide perovskites opens an enticing avenue for the rational design of chiral materials in chiroptoelectronics and spintronics. Despite several impressive approaches available to prepare 2D perovskites with chirality, it poses significant challenges to having a general route to a myriad of highquality nanoscale 2D chiral perovskites with tunable and enhanced chiroptical properties. Herein, a robust spacer cation alloying strategy to craft 2D chiral perovskite nanosheets (NSs) is reported, exhibiting a markedly improved circular dichroism signal over the pure chiral cation-based counterparts. The experimental studies and density functional theory (DFT) modeling r...

Suppression of Undesired Losses in Organometal Halide Perovskite‐Based Photoanodes for Efficient Photoelectrochemical Water Splitting

“…As a result of GTMACl treatment, the defects at the OHP/ETL interface were effectively passivated; hence, the carrier lifetime was prolonged by suppression of the non-radiative recombination of photogenerated carriers. [42,62] The passivation effect is also verified by steady-state photoluminescence (PL) spectra. The reduced PL intensity for OHP/SnO 2 /FTO sample than bare OHP/FTO sample reveals the effect of non-radiative recombination induced by defect located at interface between the OHP and SnO 2 (Figure S2, Supporting Information).…”

Chiral Lead Halide Perovskite Nanocrystals: Construction Strategies and Photophysical Properties

“…[101] Lu et al prepared perovskite nanosheets with alloyed chiral and achiral spacer cations and investigated the effect of composition on their chiroptical properties. [102] With the introduction of achiral cation phenylethylammonium (PEA) in chiral (R/S-MBA) 2 PbBr 4 , the alloyed (R-MBA 1−x PEA x ) 2 PbBr 4 nanosheets exhibited better thermal stability, reduced bandgap (60 meV) as well as red-shifted PL peak (409 to 416 nm), as illustrated in Figure 7a. In virtue of the stronger binding ability of PEA cations with the inorganic framework and the inhibition of the formation of impure 1D R-MBAPbBr 3 phases, the (R/S-MBA 1−x PEA x ) 2 PbBr 4 nanosheets displayed enhanced chiroptical activity (Figure 7b).…”

“…Meanwhile, with the increase of the concentration of achiral PEA cations, the g abs decreased gradually and its sign reversed, which can be explained by the fact that the introduction of achiral cations may change the long-range orientation of chiral cations and lead to the inversion of CD signals. [102] Figure 6. a) Schematic illustrations of chiral mono-, bi-, and tri-layer (1, 2, and 3 ML) CsPbBr 3 nanoplatelets.…”

“…Reproduced with permission. [102] Copyright 2023, Wiley-VCH. c) CD spectra of chiral CsPbBr 3 PeNCs treated with different amounts of S-PEAI (upper) and S-PEACl (bottom).…”

“…Figure 7. a) UV-vis absorption (left) and PL (right) spectra of (R-MBA1−xPEAx)2PbBr4 nanosheet solution with different x. b) CD spectra (left) and corresponding g abs at maximum CD peak (right).Reproduced with permission [102]. Copyright 2023, Wiley-VCH.…”