Contactless Detection of Giant Helicity‐Dependent Photovoltage in Chiral 2D Perovskites

ABSTRACT

Chiral‐induced spin selectivity (CISS) provides a direct route for spin filtering without magnetic fields, yet directly probing spin‐dependent charge separation in low‐dimensional hybrid perovskite systems remains elusive. Here, we systematically investigate helicity‐dependent charge‐carrier separation in chiral 2D perovskites using a novel contactless approach that employs a dynamic long‐range organization strategy to enhance the chiroptical response. By employing contactless circularly polarized time‐resolved surface photovoltage (CP‐TRSPV), we directly monitor the interplay between chirality and charge separation dynamics across multiple timescales. While typical chiro‐optical absorption in these materials is minimal, we observe a giant photovoltage anisotropy factor g_SPV of −0.7 and 0.17 for the R‐ and S‐enantiomers, respectively. This significant anisotropy, persisting from nanoseconds to milliseconds, indicates that the response is not merely a surface optical effect and is consistent with CISS‐associated spin‐polarized transport. The successful contactless demonstration of giant helicity‐dependent photovoltage substantially expands our understanding of chirality‐controlled charge dynamics and their application in spin‐optoelectronic devices.

A novel contactless probe—circularly polarized time‐resolved surface photovoltage spectroscopy is demonstrated to evaluate helicity‐dependent charge separation dynamics without the need for electrical contacts. Application of this novel methodology to chiral 2D perovskites reveals giant transient surface photovoltage anisotropy. The proposed methodology eliminates contact‐related artifacts, offering unprecedented insights into asymmetric carrier separation dynamics, accelerating the development of future spin‐optoelectronic technologies.

1. Introduction

Chiral hybrid 2D perovskites, which integrate chiral organic ligands into the inorganic framework, have recently gained significant interest as promising chiro‐optoelectronic materials [1, 2]. The incorporation of chiral organic cations is an effective strategy for inducing chirality in perovskites, leading to symmetry breaking of the entire system and guiding the crystallization into a non‐centrosymmetric, chiral‐polar point group [3]. This unique structural characteristic not only imparts chirality but also allows control of the charge, spin, and light without the need for a magnetic component [4]. Pivotal to this functionality is the Chiral‐Induced Spin Selectivity (CISS) effect [5, 6, 7], where the chiral framework acts as an intrinsic spin filter [8]. In CISS, the coupling between the electron's spin and its linear momentum mediated by the chiral potential of the lattice allows one spin orientation to pass through the material more efficiently than the other [9]. In 2D perovskites, this phenomenon is particularly effective due to the strong spin‐orbit coupling (SOC) of the heavy lead‐halide framework [10, 11], which enhances spin‐polarized transport and makes these materials ideal candidates for spin‐optoelectronic applications such as spin‐LEDs, [12, 13, 14], chiral photodetectors [15, 16, 17, 18, 19], and spin selective charge transport [20, 21], and can be exploited in designing a wide range of spintronics devices, such as memory, transistors, logic gates, and molecular q‐bits [22]. To unlock their full potential, it is crucial to understand how chemical composition and structural parameters influence their photophysical properties and mechanisms of chirality transfer. Key factors, including the choice of chiral organic molecules, framework dimensionality, octahedral distortion, and hydrogen‐bond networks, must be carefully considered [23]. Beyond intrinsic framework design, chiral doping and supramolecular arrangement act as primary drivers for the dissymmetry factor g_CD amplification, where chiral additives lead to ordered superstructures [24, 25]. Whereas typical 2D perovskites containing small organic molecules exhibit low dissymmetry factors g_CD around 10⁻⁵–10⁻⁴ [26] these strategies facilitate g_CD  amplification to 10⁻³–10⁻¹ [27], which directly translates to an enhanced chiroptical response [28].

Recent studies have demonstrated that this structural chirality enables simultaneous control of current direction and voltage magnitude via incident‐light helicity, notably via the circular photogalvanic effect (CPGE) and spin‐dependent photovoltage [29]. Although the CISS effect has traditionally been characterized through contact‐based electrical measurements [30, 31] recent advances have established terahertz (THz) emission spectroscopy as a powerful contactless probe [32]. By detecting THz radiation from photogenerated currents without metal contacts, thereby preventing signal interference from high spin‐orbit coupling (SOC) materials and ensuring the observed response is purely intrinsic of the chiral system.

Despite these advances, assessing the efficiency of chirality transfer that results in actual, enhanced chiroptical device response remains challenging, as it requires the construction of a complete optoelectronic device with two electrical contacts. Yet, the fabrication of a full device involves the formation of several heterointerfaces, which not only introduce additional interfacial defects and possible Schottky barriers but also could impact charge transport through the device. The impact of electrical contacts on charge transfer can be critical when differences in anisotropic charge transfer are small. Therefore, there is a need to develop experimental tools that enable reliable detection of anisotropic charge transport in initial stages of material research, without the need for full device fabrication.

Furthermore, understanding the temporal evolution of the CISS effect remains a frontier challenge. While ultrafast techniques such as transient absorption and terahertz emission spectroscopy have successfully probed spin dynamics on the femtosecond to picosecond timescales [32, 33, 34], a significant gap remains in understanding how these ultrafast spin states evolve into the long‐lived charge separation that governs device operation. Probing these dynamics is experimentally challenging, as contact‐based measurements introduce multiple obscuring factors, including Schottky barriers, contact resistance, and spin‐dependent charge transfer at metal‐organic interfaces that convolute the intrinsic CISS response of the chiral material [6].

In this work, we systematically investigate the helicity‐dependent charge carriers separation and dynamics in a chiral 2D perovskite system, i.e., R/S‐methylbenzylammonium (MBA) lead iodide perovskite, (R/S‐MBA)₂PbI₄, employing dynamic long‐range organization guided by chiral dopants, which enhances their chiral response [25]. We introduce a novel methodology‐ Circularly Polarized Time‐Resolved Surface PhotoVoltage (CP‐TRSPV) measurements, to directly probe the interplay between chirality and charge‐separation dynamics without the need to fabricate complete device stacks. This approach provides direct insights into the helicity‐dependent evolution of photovoltage across multiple timescales, from nanoseconds to milliseconds. We find that the R and S enantiomers exhibit pronounced anisotropic behavior with distinct photovoltage responses under right‐ circularly polarized (RCP, σ⁺) or left‐circularly polarized (LCP, σ⁻) light. The R sample shows enhanced signals under RCP light while the S sample exhibits preferential response under LCP light, with no helicity dependence observed for the racemic sample. Our approach paves the way for the contactless, time‐resolved characterization of charge separation anisotropy in chiral materials, enabling a deeper understanding of the composition‐chirality‐charge separation design rules.

2. Results And Discussion

Figure 1 illustrates the conceptual framework and experimental contact‐less strategy employed in this study to elucidate the relationship between structural chirality and enantioselective charge separation in 2D chiral perovskites. To investigate the influence of chirality on photoinduced charge separation and transport dynamics, we employ circularly polarized time‐resolved surface photovoltage (CP‐TRSPV) spectroscopy, a novel approach that enables direct probing of enantioselective photoresponse without the need for a top contact and whole device fabrication. A schematic drawing of the experimental setup is presented in Figure 1a. The setup employs a pulsed tunable laser, whose inherently linearly polarized output passes through a Rochon prism, separating the light into two orthogonally polarized beams; the unwanted component is directed to a beam dump, while the selected beam proceeds through a quarter‐wave (λ/4) plate to generate left‐ or right‐handed circular polarization, used to selectively excite the chiral material and generate spin‐polarized charge carriers. To preserve polarization purity, no reflective optics are positioned downstream of the Rochon prism, and the entire optical path from the prism to the sample is aligned along a single, fixed optical axis, with the beam propagation vector (k‐vector) kept parallel to the surface normal of each optical element, preventing out‐of‐plane reflection‐induced phase shifts that would otherwise compromise the circular polarization state. Measurements were performed in a contactless SPV capacitor configuration comprising the perovskite film on a conductive substrate (ITO) and a transparent SnO₂:F‐coated quartz cylinder separated by a mica dielectric spacer. The photovoltage signal was measured through a high‐impedance buffer. Note that all measurements were performed using back illumination (i.e., from the ITO side), with the beam impinging along the surface normal, to prevent the quartz cylinder probe from inducing polarization changes, ensuring that the incident laser polarization remains purely circular upon reaching the chiral material. TR‐SPV monitors charge carrier dynamics across an exceptionally broad temporal window, spanning more than eight orders of magnitude following nanosecond photoexcitation, enabling comprehensive tracking of processes from initial charge separation to long‐lived carrier recombination and trapping events [35, 36]. Upon pulsed laser excitation, photogeneration of charge carriers (i.e., electrons and holes) depends on the RCP or LCP light handedness. The carriers subsequently separate and migrate within the material, as schematically represented in Figure 1b. The SPV signal, which reflects the magnitude and direction of photoinduced charge separation, is measured as a function of the helicity of the incident circularly polarized light. In the electronic ground state of lead‐based perovskites, the valence band is filled with equal amounts of spin‐up and spin‐down states, right‐handed circularly polarized (RCP, σ⁺) or left‐handed circularly polarized (LCP, σ⁻) light carries photon angular momentum of ± ℏ and enables selective excitation of spin‐polarized electron‐hole pairs in accordance with angular momentum conservation (m _J = ±1). Each photogenerated electron (e) and hole (h) possess a spin momentum of S = 1/2 with a spin projection of m _S = ±1/2. Remarkably, in the presence of the Rashba effect caused by strong spin‐orbit coupling and structural asymmetry, these states undergo momentum‐dependent splitting. This lifts the spin degeneracy in the conduction and valence bands, resulting in a complex spin texture where the carrier's spin is locked to its momentum (к), further influencing spin‐relaxation dynamics.

FIGURE 1.

(a) Scheme of a circularly polarized time‐resolved surface photovoltage (CP‐TRSPV) experimental setup. (b) Illustration of the enantioselective charge generation and separation of photogenerated charge carriers, leading to surface photovoltage signals, which depend on the handedness of the incident light and the material's chirality.

By systematically varying the handedness of circular polarization and monitoring the resulting SPV response, we can directly assess the enantioselective interaction between the material's chiral electronic states and circularly polarized photons. This approach allows us to reveal how the intrinsic chirality of the perovskite framework influences charge carrier generation, separation efficiency, and preferential directional transport via contactless photovoltage detection.

2.1. Optical Properties of Chirality in 2D Hybrid Perovskites

We examined the chiroptical behavior through absorption and circular‐dichroism (CD) measurements, which uncovered several distinct features. Spectra were recorded for three sample configurations: R/S‐enantiomers, and the racemic methylbenzylammonium (MBA) lead iodide perovskite, (MBA)₂PbI₄. Each sample was prepared with chiral guiding molecules (2S,3S/2R,3R)‐­2,3‐­O‐­isopropylidene‐­1,1,4,4‐­tetraphenyl‐­1,2,3,4‐­butanetetrol, (TADDOL), as illustrated in Figure 2a. Particularly, (R‐MBA)₂PbI₄ was paired with (+)TADDOL, (S‐MBA)₂PbI₄ with (‐)TADDOL. The absorption spectra (Figure 2b, top panel) exhibit similar line shapes for the R and S perovskite samples, indicating comparable electronic band structures with minimal variation across the different configurations. All the samples exhibit characteristic excitonic features around ∼2.4–2.5 eV corresponding to the band‐edge exciton transition, suggesting that TADDOL incorporation does not alter the electronic structure. Additionally, the peaks observed at higher energies are distinctive of 2D perovskites, arising from quantum confinement effects [37, 38], that transform the energy‐level continuum of bulk materials into discrete levels [39].

FIGURE 2.

(a) Schematic representation of the sample set (b) Upper panel: absorption spectra; lower panel: circular dichroism (CD) spectra for the set of chiral samples.

The CD spectra (bottom panel, Figure 2b) of the R and S perovskites exhibit broadly similar line shapes with opposite polarity. Each CD feature correlates with a specific absorption peak and can be assigned to different excitonic transitions [40] (n = 1, n = 2, etc.), demonstrating that the chiral supramolecular arrangement induces differential absorption of left‐ and right‐circularly polarized light across the entire manifold of excitonic states. The primary excitonic transitions for both enantiomers align precisely at ∼2.48 eV, confirming that the macroscopic electronic bandgap is identical in the two enantiomeric systems. Minor variations in CD peak intensity, shape, or zero‐crossing positions arise from local structural asymmetries, specifically subtle differences in octahedral tilt angles (Pb‐I‐Pb bond angles) induced by chiral cation packing rather than any modification to the bulk optical bandgap [41].

In contrast, the racemic perovskites exhibited only a subtle CD signature near the excitonic peak upon introduction of (+)‐TADDOL (Figure S1), arising from the preferential interaction of the chiral dopant with one of the chiral conformers present in the racemic lattice. Since the sample remains macroscopically racemic, this induced chiral activity is insufficient to produce an observable effect in the CP‐TRSPV measurements.

The anisotropy g_CD factor values for the chiral perovskite series defined as

$$g_{CD}=\frac{2\left(A_{LCP}-A_{RCP}\right)}{\left(A_{LCP}+A_{RCP}\right)}$$

with A_LCP and A_RCP corresponding to the absorbances under left‐ and right‐circularly polarized light, respectively. This parameter quantifies the strength of chiral transfer through differential absorption of circularly polarized light [42, 43].

As a reference, (R/S‐MBA)₂PbI₄ without TADDOLs shows only weak chiroptical activity, with g_CD ≈ ± 3 × 10^{− 4} (CD spectra shown in Figure S2). Upon incorporation of TADDOLs, the anisotropy factor increases by approximately one order of magnitude, reaching +4.2 × 10^{− 3} for the R‐perovskite and −6.0 × 10^{− 3} for the S‐perovskite. This pronounced enhancement demonstrates the strong role of TADDOLs in reinforcing chiral coupling between the organic cations and the inorganic lead–halide framework [25].

Next, we set out to study how the chiro‐optical properties translate directly to anisotropic charge separation across the perovskite films, using CP‐TRSPV, as shown below.

2.2. Time‐Resolved SPV Under Circularly Polarized Light

Time‐resolved SPV measurements (Figure 3) reveal clear differences in charge separation dynamics between the R‐ and S‐perovskite films under RCP and LCP illumination. It is important to note that since we did not fabricate full device stacks, or even employ any charge‐selective layers in our study, the actual charge separation direction, which can be dictated either by band bending in the ITO/perovskite back interface, or surface band‐bending of the perovskite, is of less importance, and rather, we focus on the differences between the light polarization and its interaction with the respective perovskite enantiomer.

FIGURE 3.

Circularly polarized time‐resolved surface photovoltage (CP‐TRSPV) spectroscopy of chiral perovskite thin films. Contour plots of time‐resolved SPV spectroscopy and helicity‐dependent differences, where each row corresponds to a different sample: (top row) (R‐MBA)₂PbI₄, (middle row) (S‐MBA)₂PbI₄, and (bottom row) (rac‐MBA)₂PbI₄. From left to right, the columns represent the SPV response under right‐handed circularly polarized light (RCP, σ⁺), left‐handed circularly polarized light (LCP, σ⁻), and the resulting helicity‐dependent difference map $(\mathrm{\Delta }{V}_{SPV}=V_{LCP,{\sigma }^{-}}-V_{RCP,{\sigma }^{+}})$, plotted as a function of excitation energy (2.0–2.8 eV) and decay time.

The contour plots of time‐resolved SPV spectroscopy illustrate that the photovoltage response spans a broad energy range from 2.0 to 2.8 eV, with the most intense signals centred around the excitonic transition. The R‐sample (Figure 3, top row) initially exhibits a positive SPV signal, indicating hole transfer to the surface, followed by a transition to negative signals at the µs timescale, suggesting electron accumulation on the surface under both polarizations. However, this response is strongly anisotropic; under RCP light (σ⁺), the signal remains positive for a longer duration, with the positive ΔV_SPV  emerging immediately in the nanosecond regime and persisting prominently up to ∼10^{− 4} s before undergoing significant decay, whereas, under LCP light (σ⁻) it switches to a negative signal at a significantly earlier timescale (∼10^{− 6} s). In contrast, the S‐sample (Figure 3, middle row) is dominated by a positive signal across the entire time range, indicating preferential hole transfer to the surface without the parallel competing process observed in the R‐sample. The S‐sample also exhibits strong anisotropy with an enhanced SPV response under LCP (σ⁻) compared to RCP (σ⁺), displaying a helicity preference exactly opposite to that of the R‐sample, and a dominant positive signal across the entire time range indicating preferential hole transfer to the surface without the parallel competing process observed in the R‐sample. This LCP‐preferring response is consistent across the broader spectral range, except for a narrow sign inversion in ΔV_SPV near the excitonic resonance (∼2.4 eV), likely reflecting a resonance‐activated competing trapping channel at maximal carrier density. Importantly, for the racemic sample (Figure 3, bottom row), no significant difference in photovoltage response is observed between RCP and LCP light as confirmed by the minimal contrast in the difference map.

In addition, since the racemic sample possesses essentially the same ITO/perovskite interface as the chiral samples, this absence of a helicity‐dependent response rules out interface‐induced effects (e.g., band bending or trap states at the ITO/perovskite interface) as the dominant origin of the SPV anisotropy, and confirms that the helicity‐dependent behaviour observed for the R and S enantiomers arises specifically from the chiral nature of the perovskite structure.

To exclude artifacts arising from fluctuations in incident light intensity, we ensured that the laser intensity remained nearly constant for both σ⁺ and σ⁻ at the measured photon energy, as shown in Figure S3. This confirms that the differential photovoltage responses to σ⁺ and σ⁻ originate from intrinsic material properties rather than variations in incident light intensity, leading to spin‐dependent charge separation. Although spin lifetimes reported for comparable chiral perovskite systems are in the picosecond range [25], much shorter than the nanosecond pulse duration employed here, the helicity‐dependent SPV persists over the entire measurement window. It is important to note that this prolonged signal does not signify a long‐lived spin state. Rather, the spin‐filtering effect acts exclusively during the initial excitation to modulate the yield of separated charge carriers. Once separated, this larger carrier population decays via standard, spin‐independent perovskite kinetics, specifically trapping/de‐trapping at defect sites and potential ion migration, thereby preserving the helicity‐dependent amplitude differences across the entire temporal profile.

To compare the tr‐SPV decays under LCP and RCP in detail, Figure 4 presents the helicity‐dependent charge carrier dynamics. The transient SPV measurements show that while R‐ and S‐perovskite enantiomers are electronically indistinguishable under linear polarization (Figure S4), they display significant differences under circularly polarized excitation. Furthermore, under linearly polarized light, both samples have comparable peak photovoltage magnitudes and exhibit nearly identical decay profiles, confirming similar film quality and achiral electronic properties. Circularly polarized excitation reveals a clear divergence in their charge‐carrier dynamics. In the short‐time regime (left panel, up to ∼150 ns, Figure 4a), both enantiomers exhibit similar initial charge separation kinetics within 10–20 ns, but their subsequent kinetics diverge significantly depending on helicity matching. R‐perovskites under RCP excitation (red) reach a sharp peak of about 3.5 mV around 18 ns before gradually decaying, while under LCP excitation (blue curve), they show much lower signals (∼2.5 mV) throughout. Conversely, S‐perovskites prefer the opposite helicity, with a stronger photovoltage response under LCP excitation. To further verify the reproducibility and reliability of the CP‐TRSPV method, spectra recorded at diverse times across distinct synthesis batches show a consistent appearance of the helicity‐dependent differential response for both R and S chiral perovskites (see Figure S5), confirming that the observed anisotropy is an intrinsic chiroptical property of the chiral perovskite structure rather than an experimental artifact or random fluctuation.

FIGURE 4.

Helicity‐dependent charge carrierdynamics under excitation at 2.4 eV. (a) Zoom on charge‐separation regime (0–150 ns): CP‐TRSPV signals under RCP (red) and LCP (blue) excitation, showing distinct temporal profiles for the R‐ and S‐enantiomers. (b) Logarithmic timescale up to 0.01 sec of the normalized decays for both samples. extending to the ms regime, revealing mirror‐symmetric helicity selectivity.

Besides the difference in signal magnitude, their temporal behaviours also differ: R‐perovskites rise and decay more sharply, whereas S‐perovskites show more gradual kinetics, stabilizing between 30 and 60 ns, after which a plateau is reached.

The normalized decay curves in the long‐time regime (Figure 4b) show persistent chirality‐dependent selectivity, with R‐perovskites (top panel) showing higher signal under RCP (red curve), and S‐perovskites (bottom panel) under LCP (blue curve) excitation. In the time domain, all samples initially exhibit a short negative signal in the nanosecond regime, followed by a rapid rise to positive polarity around ∼10⁻⁸ s, after which the signals evolve differently for σ⁺ vs. σ⁻ excitation. Importantly, these helicity‐matched curves remain mirror‐symmetric and do not overlap for over 10 ms. Notably, the SPV signal of the R‐perovskite undergoes a sign reversal at ∼10^{− 6} s, transitioning from positive to negative, while the S‐perovskite maintains a positive signal throughout the entire decay up to 10^{− 2} s. This sign reversal in the R‐sample likely arises from two competing charge separation processes occurring in parallel; the additional process results in electron accumulation near the surface, possibly related to the presence of positively charged surface defects acting as deep electron traps, which dominate at longer timescales and flip the sign of the SPV signal. Overall, we find that the initial rise slopes of the SPV transients are very similar for LCP/RCP excitation, while the peak SPV amplitudes and recombination kinetics differ significantly. These results suggest that while the initial charge separation dynamics remain similar, the chiral framework functions as an intrinsic spin filter, suppressing recombination pathways that sustain charge separation over a broad temporal range, extending well beyond the initial excitation event.

We found that the photovoltage response varied depending on both the circular polarization of light (LCP or RCP) and the enantiomer (R‐ or S‐form). To quantify this effect, in analogy to the current anisotropy factor for circulary polarized light (CPL) detectors [44], we introduce the SPV anisotropy factor, g_SPV , expressed as:

$$g_{SPV}=\frac{2\left(V_{LCP}-V_{RCP}\right)}{\left(V_{LCP}+V_{RCP}\right)}$$

and V_LCP  and V_RCP are the photovoltage responses generated under LCP or RCP light, respectively.

Figure 5 illustrates the evolution of g_SPV  as a function of photon energy, which closely tracks the g_CD spectra, and exhibits strong energy dependence, with the largest value observed at the first excitonic absorption peak (∼2.4 eV), reaching g_SPV = −0.7 for R perovskites, and 0.17 for S perovskites. Similar wavelength‐dependent behavior has been reported for chiral 2D perovskite‐based CPL detectors, with maximum photocurrent response occurring at the excitonic absorption peak window [45].

FIGURE 5.

Spectral evolution of g_SPV and g_CD for R‐ and S‐perovskites. The g_SPV values (markers) were calculated from SPV transients as the maximum amplitude difference between LCP and RCP illumination after the signals, after the rise time, corresponding to maximal charge separation before recombination onset. The g_CD values (dashed lines) from CD measurements are shown for comparison. R‐perovskite (magenta); S‐perovskite (purple).

When comparing the value of the photovoltage anisotropy factor g_SPV  to the absorption anisotropy factor, g_CD , as shown in Figure 5, g_SPV exceeds g_CD  in 3 orders of magnitude, indicating that the photovoltage response cannot be explained solely by differential absorption. This enhancement suggests that additional chiral‐dependent processes, including asymmetric charge separation, spin‐selective charge transport, and reduced recombination, play a decisive role in charge carrier dynamics. The large g_SPV values measured here therefore serve as a figure‐of‐merit for spin‐selective charge transport, consistent with the amplified transport‐level chirality reported via photocurrent measurements in other chiral perovskite systems. This is consistent with prior photocurrent measurements on the similar (R/S‐MBA)₂PbI₄ system [29], which similarly found that transport‐level chiral anisotropy substantially exceeds the optical absorption asymmetry, attributing the difference to spin‐selective charge transport rather than differential absorption. To further evaluate the effectiveness of the contactless CP‐TRSPV technique, it is instructive to compare our findings with reports in the literature that utilize conventional, contact‐based electrical measurements. For the identical chiral 2D perovskite system investigated here, previous contact‐based photocurrent studies on fully fabricated optoelectronic devices reported a remarkably high dissymmetry factor of photocurrent g_ph = |1.16| [25]. In comparison, our contactless approach yields a surface photovoltage dissymmetry factor of g_SPV = |0.7|. Given that the maximum theoretical value for the dissymmetry factor, regardless of its physical origin, is 2, both approaches yield very large values for this material system, among the highest reported in the literature, corroborating the exceptionally strong chiroptical response of this material system and the overall agreement between the two approaches. However, these two values probe fundamentally distinct stages of the photoelectric process and are not directly equivalent. The contact‐based g_ph reflects the macroscopic device response, which inherently encompasses bulk charge transport, carrier collection efficiencies, and potential asymmetries arising from electrode geometry or heterointerfaces. Conversely, our g_SPV directly probes the photovoltage asymmetry arising from the combination of intrinsic chiral absorption and initial spatial charge separation at the material surface, entirely free from contact‐induced artifacts or interface perturbations. The slight divergence between these values highlights how downstream device architecture can amplify or modulate a material's intrinsic response, further highlighting the utility of CP‐TRSPV as a clean, processing‐independent probe of the material's intrinsic chirality.

Notably, such a disparity between g_CD and g_SPV has been widely observed across chiral perovskite systems.Yang et al. [45] recently reported that g_CD (0.001–0.004) in chiral perovskite CPL detectors is typically two to three orders of magnitude lower than photocurrent dissymmetry factor of g_ph  (0.1–1.84), explicitly noting that the origin of this discrepancy remains elusive and that additional mechanisms beyond chiroptical absorption must contribute. We attribute this amplification to the CISS effect, whereby the chiral crystal lattice acts as a spin‐dependent filter that selectively separates photogenerated carriers according to their spin orientation, translating a small absorption asymmetry into a significantly larger population difference in charge‐separated carriers. In this framework, the modest absorption asymmetry (g_CD ∼ 10^{− 3}) reflects only the initial photon absorption probability. As photogenerated carriers subsequently migrate through the chiral lattice, the crystal framework functions as a spin‐dependent filter via the CISS effect. Carriers with the favored spin orientation undergo spatial separation more efficiently, while carriers of the opposite spin orientation are more likely to undergo recombination that does not contribute to charge separation. This step effectively translates a small spin‐filtering bias into a significantly larger population difference in separated electron‐hole pairs for one light helicity relative to the other. Once separated, this larger carrier population evolves via conventional built‐in‐field and spin‐independent trapping/recombination kinetics. Thus, the final measured g_SPV reflects the outcome of this initial spin‐selective spatial separation step rather than the prolonged preservation of the spin state itself, which relaxes on a picosecond timescale.

Numerous research groups worldwide are pursuing efforts to exploit the CISS effect to enhance the efficiency of existing optoelectronic devices and to develop novel polarization‐dependent optoelectronic devices. However, to date, still little is known regarding the structure‐property relationships in these chiral materials, and especially how the CD translates to the CISS effect, measured in full devices as g_ph , or g_CPL , if at all. Device fabrication is also time‐consuming and introduces variables such as interface defects or contact asymmetries that can obscure the material's intrinsic properties.

In our work, we suggest an alternative, contactless approach that quantifies the CISS effect in chiral halide perovskites (and can be applied to other classes of chiral materials) and enables direct measurement of this effect without the need to fabricate a full device structure. This method could be readily extended to measure numerous chiral materials under many different synthesis routes and chemical permutations, offering a fast and robust route toward the structure‐property relations that remain urgently needed in this field.

Interestingly, while the g_SPV  values for the two enantiomers exhibited opposite signs, the magnitudes were asymmetric, with R‐perovskites showing significantly higher values than S‐perovskites. Similarly, Liu et al. [33] observed a distinct asymmetric response in chiral 2D perovskite single crystals, with the R‐enantiomer consistently showing a higher dissymmetry factor of circularly polarized luminescence, g_CPL values than the S‐enantiomer. They postulate that this discrepancy arises from differences in enantiomeric composition inherited from the chiral organic precursors (enantiomer ratio ∼98%), with crystallographic refinement (Flack parameter) suggesting an enantiomeric purity of around 95% in the grown crystals. However, Paltiel et al. [46] recently proposed an alternative explanation, suggesting that the difference in spin polarization between the two enantiomers in chiral systems is attributed to the alignment of the total angular momentum vector (J), comprising the orbital and spin angular momentum. The projection of the J depends on the magnetic anisotropy caused by the spin‐orbit coupling (SOC) and asymmetry of the molecular field. Although both enantiomers share the same magnitude J, their vectors may be oriented differently within the molecular frame. This directional asymmetry, quantified by the angle between J and the molecular dipole moment (μ), drives the differential spin‐polarization observed in electron transport and creates enantiomer‐specific interactions with other chiral entities like chiral fields, light, and spin‐polarized free electrons.

3. Conclusions

In summary, polarization‐dependent tr‐SPV measurements reveal a distinct divergence in charge separation dynamics between (R‐MBA)₂PbI₄ and (S‐MBA)₂PbI₄ thin films under circularly polarized excitation. The observed anisotropic behavior, characterized by enhanced surface photovoltage signals for the R‐enantiomer under RCP and the S‐enantiomer under LCP, demonstrates that helicity‐dependent carrier generation is coupled to the material's structural handedness. This selectivity extends significantly beyond the initial excitonic absorption; the temporal evolution of the tr‐SPV transients indicates that the structural chirality of the perovskite lattice actively governs the subsequent charge‐carrier kinetics and surface accumulation. By establishing spin‐polarized recombination pathways, the chiral framework acts as an intrinsic filter that sustains charge separation into the microsecond and millisecond regimes, providing the first experimental evidence for chirality‐induced prolonged charge separation kinetics in this class of materials.

Ultimately, these findings highlight the potential of chiral hybrid perovskites for advanced optoelectronic and spintronic applications, in which structural symmetry breaking is leveraged to modulate the magnitude, polarity, and lifetime of photogenerated carriers without requiring an external magnetic field. Our novel contactless methodology paves the way for rapid assessment of the optoelectronic chiral response in 2D chiral halide perovskites, to establish the well‐needed structure‐property design rules in this field. Unlike conventional device‐based measurements of CISS‐driven charge transport, which involve many post‐processing steps and metal contact deposition, susceptible to confounding factors such as interface defects and contact asymmetries, our approach enables direct quantification of spin‐selective charge separation without the need to fabricate a full device structure. This method could be readily extended to a broad range of chiral materials across diverse synthesis routes and chemical permutations, supporting the broader effort to obtain the much‐needed structure‐property relations in a fast and robust manner, and harnessing CISS for next‐generation spintronic and optoelectronic devices.

4. Experimental Section

4.1. Materials

(R)‐(+)‐α‐methylbenzylamine (R‐MBA,98%, optical purity > 97%), (S)‐(−)‐α‐methylbenzylamine (S‐MBA,98%, optical purity > 97%), α‐methylbenzylamine (racemic‐MBA,99%), N,N‐anhydrous dimethylformamide (DMF) were purchased from Sigma‐Aldrich. 57% aqueous hydriodic acid (HI) solution (99.95%, stabilized by H₃PO₂) was purchased from Thermo Fisher Scientific. Lead (II) iodide, 99,9985% (metal basis) was purchased from Thermo Scientific Chemicals. Diethyl ether AR, acetone (99.8%) and isopropanol (99.5%) were purchased from (BioLab) (2S,3S/2R,3R)‐2,3‐ O‐ isopropylidene‐ 1,1,4,4‐ tetraphenyl‐ 1,2,3,4‐butanetetrol, (+/−)‐TADDOLs were purchased from TCI Chemicals (Tokyo, Japan). All reagents were used without further purification.

4.2. Synthesis of R/S/rac‐MBAI

The R‐, S‐, and rac‐MBAI salts were synthesized by dissolving the corresponding MBA precursor (5 mL) in 30 mL of ethanol in an ice bath. An aqueous solution of hydroiodic acid (HI) (5.8 mL) was added dropwise to the flask with vigorous stirring. After the HI solution was added, the mixture was allowed to stand in an ice bath for 1 h. The crude product was obtained by slowly evaporating the solvent under reduced pressure until the liquid became highly viscous. To induce crystallization, 15 mL of diethyl ether was added to the residue and stirred until a white precipitate formed. The precipitate was filtered under vacuum and washed thoroughly with diethyl ether until the color became white. Finally, the product was dried in a vacuum oven at 60°C for 12 h.

4.3. Thin Film Preparation

All precursor and thin film fabrication steps were performed in an N₂‐filled glove box. The (R/S/rac‐MBA)₂PbI₂ precursor solutions were prepared by dissolving PbI₂ and (R/S/rac)‐MBAI (1:2 molar ratio) in anhydrous DMF. The concentration of (R‐/S‐/rac‐MBA)₂PbI₄ precursor solutions was 0.5 M. Prior to deposition, ITO glass substrates were cleaned by sonication in deionized water/acetone/isopropanol for 15 min each, followed by 10 min UV‐ozone treatment. For the thin film deposition, 60 µL of 0.5 M perovskite solution in DMF containing (±)‐TADDOL at 12% of molar ratio relative to chiral cations was dispensed on the ITO glass substrate. The spin‐coated film was annealed at 100°C for 10 min on a hotplate.

4.4. Circularly Polarized Time‐Resolved Surface Photovoltage Spectroscopy (CP‐TRSPV)

Transient SPV measurements were performed in an N₂ environment using a diode‐pumped tunable pulse laser (Nd:YAG, EKSPLA, NT230‐100, duration time of laser pulses 2–3 ns) equipped with a spectral cleaning unit. To generate circularly polarized light, a Rochon prism was employed to produce linearly polarized light, followed by a quarter‐wave plate λ/4 (Thorlabs) with the fast axis oriented ±45° relative to the incident light. The light source was focused onto the sample surface with an illumination spot size of 7 mm in diameter, corresponding to an effective optical sample area of approximately 0.385 cm². At 2.5 eV, the laser provided an average power of ∼10 mW and a mean pulse energy of ∼6 × 10^{− 4} J, resulting in an incident power density of ∼26.0 mW/cm². The measured power and pulse energy across the full spectral range for all three polarization states are shown in Figure S6. The measurement frequency was 16 Hz, 20 averages were taken per transient, and the laser intensity was controlled using neutral density filters. The SPV transients were measured with an oscilloscope card (Gage, RazorMax PCIe CSE161G2, 4GS, 1 GS/s) using in‐house developed software for logarithmic readout. The samples were excited from the back side in a fixed‐capacitor configuration. The setup incorporated a high‐impedance buffer, and a mica sheet served as the spacer between the probe head and the sample.

4.5. Absorption and CD Measurements

Absorption and CD measurements of the thin films were carried out using a J‐1500 spectrometer (JASCO) in the range of 250–550 nm wavelength using a custom‐built sample holder.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: smll74908‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.