REVIEW 3 major objections 4 minor 5 references
Engineering Chirality in Halide Perovskites
T0 review · 3 major / 4 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read The paper claims that chirality can be written into halide perovskites during crystal growth by rotating the substrate during glancing-angle deposition, producing crystallographic torsion with absorption dissymmetry up to 0.6 and…
desk verdict Real effect, strong handedness controls, but the central mechanism claim—crystallographic torsion—is not actually separated from twisted ribbon morphology; the paper deserves review but the authors will need depth-resolved texture evidence. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is growth-controlled crystallographic torsion: during glancing-angle deposition, substrate rotation preserves the PbI2 c-axis tilt while progressively rotating its in-plane azimuth, yielding a twisted crystalline texture rather than a helical morphology. The tuneable control parameter is the vertical pitch, defined as the film thickness deposited during one complete substrate rotation; smaller pitches mean more twist per unit height. The other load-bearing tool is front-back averaging, in which circular-dichroism spectra are recorded with the film facing the beam and then flipped 180 degrees; averaging cancels the dominant linear-dichroism and linear-birefringence artifact and isolates the genuine chiroptical component.
What would settle it
Map the local crystal orientation inside a single 6.7-micrometre-pitch ribbon along its growth direction using nanobeam or 4D-STEM diffraction: if the orientation does not rotate continuously with height but instead jumps among discrete azimuths consistent with a static mosaic of domains, the torsion interpretation would be falsified.
Extended reading notes
Core claim
The central discovery is growth-controlled crystallographic torsion as an origin of chirality in halide perovskites. During glancing-angle deposition at a fixed zenithal angle of 85 degrees, continuous substrate rotation progressively rotates the in-plane crystallographic orientation of PbI2 while preserving the c-axis tilt near 75 degrees, creating a twisted texture. The degree of torsion is set by the vertical pitch, the thickness deposited per full 360-degree rotation: the chiroptical response grows as the pitch decreases, peaks at 6.7 micrometers, and then weakens and reverses at smaller pitches. The strongest PbI2 samples show a chiroptical ellipticity of about 19 degrees and an absorption dissymmetry factor near 0.6, with handedness selected by the rotation direction. Vapour-phase conversion transfers the twist into MAPbI3, FAPbI3, CsPbI3, MAPbI2Br, and FAPbI2Br, giving circularly polarized luminescence with dissymmetry factors up to 0.23.
Load-bearing premise
The load-bearing premise is that the chiroptical signal originates from crystallographic torsion within the crystals, rather than from the twisted ribbon-shaped morphology visible in electron microscopy or from residual linear anisotropy that front-back averaging does not fully remove.
Editorial extensions
If this is right
- Reversing the substrate rotation direction flips the handedness of the chiroptical response, yielding nearly mirror-symmetric spectra with opposite signs.
- The vertical pitch provides a continuous tuning knob: the chiroptical response grows as pitch decreases, peaks at 6.7 micrometres, then shrinks and reverses sign at 1.7 micrometres.
- The chirality programmed into PbI2 survives vapour-phase conversion into five halide perovskite compositions, so bandgap and composition can be varied without losing the optical activity.
- The strongest response cannot be explained by circular Bragg reflection, because the 6.7-micrometre-pitch film is only 2.5 micrometres thick and would place any Bragg resonance in the mid-infrared.
- The approach achieves strong chiroptical responses without chiral molecular ligands, enantiomorphic space groups, or external photonic architectures.
Reading between the lines
- If crystallographic torsion is the active mechanism, the same substrate-rotation recipe should imprint chirality in other textured vapour-deposited semiconductors; repeating the experiment with a non-perovskite layered material such as SnS2 or BiI3 would be a direct transfer test the paper does not perform.
- Because handedness is set by a mechanical rotation direction rather than by molecular synthesis, the method may extend naturally to large-area or roll-to-roll deposition, although the paper does not address scalability.
- Absorption dissymmetry near 0.6 suggests the films could act as compact circular polarization filters, but the paper reports dissymmetry values rather than device figures such as extinction ratio or transmission bandwidth.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports a glancing-angle-deposition (GLAD) process for PbI2 in which the substrate is rotated azimuthally during growth, producing twisted ribbon-like nanostructures with strong chiroptical responses: ellipticities up to 19°, absorption dissymmetry factors gabs-chirop approaching 0.6, and, after vapour-phase conversion to several halide perovskites, circularly polarized luminescence with glum values up to ±0.23. The central claim is that the chiroptical response originates from growth-controlled crystallographic torsion, i.e., progressive rotation of the in-plane crystallographic orientation during growth while the c-axis tilt is preserved, rather than from molecular chirality, helical morphology, or photonic architecture. Evidence includes XRD pole figures and reconstructed ODFs, handedness reversal by reversing substrate rotation, front-back averaging to remove linear-dichroism/linear-birefringence (LDLB) contributions, and comparison with non-rotating (VP=∞) and rapidly rotating (VP~0) control samples.
Significance. If the proposed mechanism is correct, this would be a genuinely new route to chiral halide perovskites, avoiding chiral molecular building blocks and external chiral photonic structures, and it would open a growth-based design axis for spin-optoelectronic and circularly polarized light applications. The paper has notable strengths: the handedness inversion is an independent and convincing check; the gabs estimate is explicitly conservative (Supplementary Fig. S11); the front-back averaging protocol addresses the well-known LDLB artifact; and the Supplementary Information provides unusually detailed motor, software, and hardware information for replication. However, the central attribution of the chiroptical response to crystallographic torsion is not uniquely established by the reported data, and the alternative explanation based on the twisted ribbon morphology is not fully excluded.
major comments (3)
- [Growth-controlled crystallographic torsion (Fig. 2b-g)] The pole-figure and ODF measurements are volume-averaged and cannot distinguish a continuous twist of crystallographic orientation during growth from a static mosaic of azimuthally misoriented domains. The broadening of the (0003) maxima into a ring at ψPF≈75° and the broadening of the φ1 distribution are equally consistent with either interpretation. The text states that this 'provides direct evidence of growth-controlled crystallographic torsion,' but the data shown do not support a unique conclusion. Please add depth-resolved or otherwise orientation-selective evidence, e.g., cross-sectional TEM/4D-STEM nanodiffraction, synchrotron micro-beam scanning through the film thickness, or quantitative fitting of the ODF with a torsion model, to demonstrate that the in-plane orientation rotates progressively with growth time.
- [Growth-encoded chirality in PbI2 nanostructures as perovskite precursors; Supplementary S5] Figure 1b shows twisted ribbon-like nanostructures, so a chiral shape is present independently of any crystallographic twist. The front-back averaging described in Methods removes the second-order LDLB term, but it does not remove differential scattering or form chirality arising from the chiral morphology. Supplementary S5 explicitly rules out only the circular Bragg phenomenon, which requires multiple full turns and a well-defined helicoidal axis; it does not address broadband form birefringence, Mie-type scattering, or other shape-related chiroptical mechanisms. Therefore the load-bearing premise that crystallographic torsion, rather than the twisted ribbon morphology, is the origin of the measured CD is underdetermined. Please provide a control that preserves the ribbon morphology while removing the crystallographic torsion, or quantitative electromagnetic modelling of the measured ribbon geometry with and without crystallographic anisotropy.
- [Growth-encoded chirality in PbI2 nanostructures as perovskite precursors (VP~0 control, Fig. 1e and Supplementary Fig.] The VP~0 rapid-rotation control is not a morphology-matched control. The main text itself notes that high-speed rotation modifies the structural organization, and Supplementary Fig. S3 shows markedly different absorbance profiles with additional features near 550 and 650 nm for VP~0. Consequently, the weak chiroptical response of VP~0 (θchirop~0.3°) cannot be used to isolate the role of crystallographic torsion, because both the crystallography and the ribbon geometry differ from the samples with intermediate VP. Please report SEM images of the VP~0 film and, if possible, design a control in which the morphology is unchanged while the in-plane crystallographic rotation is suppressed, or otherwise model the expected chiroptical signal from the morphology alone.
minor comments (4)
- [Methods; throughout] The notation 'VP~0' is used both for 'maximum rotation speed' and for 'VP=8 nm'; please define this once in the Methods and use it consistently in the main text and figures.
- [Methods; Supplementary Fig. S11] The comparison between averaged and measured unpolarized absorbance is useful, but the discrepancy at long wavelengths raises the question of whether the same averaging choice affects the CPL glum calibration. Please state explicitly whether an analogous systematic check was performed for the photoluminescence measurements.
- [Supplementary S5] The Bragg-wavelength estimate assumes a pitch of 6.7 μm, but the accumulated twist over the 2.5 μm film thickness is only about 135°. Please state this assumption explicitly in the text so that the reader can follow the reasoning without referring to the Methods.
- [Figure 3l] The figure caption reports error bars for glum but does not define the number of independent samples or the number of measurement repetitions per sample. Please clarify this in the caption or in the Methods.
Circularity Check
No significant circularity; the central claim rests on independent XRD, SEM, and handedness controls, with self-citations only contextual and not load-bearing.
full rationale
The paper's central claim—that controlled substrate rotation during glancing-angle deposition produces growth-controlled crystallographic torsion and large chiroptical responses—is supported by measured quantities rather than by fitted parameters or by the paper's own conclusions. The XRD pole figures and reconstructed ODFs are experimental data; the front-back averaging procedure and the conservative gabs estimation are standard and are validated against an unpolarized absorbance measurement (Supplementary Fig. S11). The handedness-reversal experiments provide an independent check, and the circular Bragg reflection alternative is explicitly ruled out using the pitch, thickness, and refractive index estimates in Supplementary Information S5. The only self-citation (ref. 31, prior GLAD PbI2 nanowalls) is contextual: the current manuscript independently reports the baseline XRD texture, and the earlier TEM observation is supplementary rather than the load-bearing proof of the central mechanism. The possible ambiguity between continuous crystallographic torsion and a static mosaic of azimuthally disordered domains is an interpretational underdetermination, not a circular reduction by the paper's own equations. No step identified fits the enumerated circularity patterns: no definitional equivalence, no fitted input renamed as prediction, and no load-bearing self-citation chain. Score 1 reflects only the minor, non-load-bearing presence of self-citation for prior baseline work.
Assumptions & free parameters
assumptions (5)
- domain assumption The (0003) reflection directly probes the crystallographic c-axis orientation in hexagonal PbI2.
- domain assumption The LDLB contribution reverses sign when the sample is flipped by β=180°, so front-back averaging isolates the chiroptical component.
- domain assumption The crystal orientation follows the azimuthal direction of the deposition flux during growth.
- domain assumption The ODF reconstructed from three pole figures (0003), (10-11), (11-20) is sufficient to describe the texture.
- domain assumption The circular Bragg phenomenon requires many turns and a well-defined helicoidal axis and therefore cannot explain the response.
Cite this review
Pith. "Pith review of Engineering Chirality in Halide Perovskites." pith.science (2026). https://pith.science/paper/T24QB4VS
@misc{pith2026260813053,
author = {Pith},
title = {Pith review of: Engineering Chirality in Halide Perovskites},
year = {2026},
howpublished = {\url{https://pith.science/paper/T24QB4VS}},
note = {Machine review of arXiv:2608.13053}
}
read the original abstract
The ability to control chirality in halide perovskites offers new opportunities for circularly polarized photonics, spin-selective electronics, and quantum information technologies. Chirality in halide perovskites is commonly achieved through chiral molecular building blocks or externally imposed photonic architectures. Although both approaches can generate strong chiroptical responses, many spin-dependent functionalities require structural symmetry breaking embedded within the material itself. Here we show that chirality can emerge directly during crystal growth. By combining glancing angle deposition with controlled substrate rotation, we generate highly textured PbI2 nanostructures with growth-controlled crystallographic torsion. X-ray texture analysis reveals that substrate rotation progressively rotates the crystal orientation during growth while preserving the c-axis orientation, resulting in a twisted texture with giant and tuneable chiroptical responses, including ellipticities of 19{\deg} and absorption dissymmetry factors approaching 0.6. The chirality programmed during growth is transferred through vapour-phase conversion into multiple halide perovskite compositions, resulting in circularly polarized luminescence with glum values up to 0.23. These findings establish growth-controlled crystallographic torsion as a previously unexplored origin of chirality in halide perovskites.
Reference graph
Works this paper leans on
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[2]
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[4]
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[5]
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work page 2014
Reviewed August 15, 2026 · model on record in the stance chip above.
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