Horizontally oriented compact colloidal quantum well films enable efficient and stable electroluminescent diodes

Domain: physics
Published: 2025-12-01
Editorial outcome: major_revision

Abstract
Colloidal quantum well-based light-emitting diodes are highly promising for electroluminescent applications owing to their high fraction of horizontally aligned transition dipole moments, but scalable fabricating their films with dominant horizontal dipole orientation for electroluminescent devices remain major challenges. Here, we utilize a two-phase driving flat arrangement strategy combined with Langmuir–Schaefer technology to create compact colloidal quantum well films with predominantly horizontal dipole alignment. The interfacial driving force between the two liquid phases facilitates the formation of uniform, densely packed films, which exhibit 90% horizontal dipole alignment, yielding a light extraction efficiency of 35.8%. The resulting devices achieve (4 mm2) an external quantum efficiency of 25.5%, a maximum luminance of 59,620 cd m−2, and outstanding operational stability (T95 @100 cd m−2 > 16,233 h). Moreover, this technique enables scalable fabrication of uniform colloidal quantum well films (100 cm2), maintaining luminance above 60,000 cd m−2 in 4 cm2 devices, indicating industrial feasibility.

Introduction
Colloidal quantum wells (CQWs) have attracted considerable attention as next-generation light-emitting materials due to their tunable emission, ultranarrow linewidths, near-unity photoluminescence quantum yields (PLQYs), and exceptional stability1–8. Their quasi-two-dimensional structure imposes strong vertical quantum confinement while preserving delocalized in-plane excitons, yielding oriented transition dipole moments (TDMs) and enhanced light outcoupling, with theoretical EQEs approaching ~40%—well above conventional emitters9,10. The first CdSe CQW-based LEDs reported by Chen et al. in 2014 demonstrated an external quantum efficiency (EQE) below 1% and moderate brightness levels, highlighting the early-stage limitations of CQW device performance11. In recent years, CQW-based LEDs have developed rapidly. A notable improvement was realized in 2019, when Kelestemur et al. demonstrated CdSe/CdS/CdZnS heterostructured CQW LEDs with nearly 10% EQE12. In 2020, subsequent optimization of the device configuration, particularly the adoption of an inverted architecture with CdSe/CdZnS CQWs, enabled Liu et al. to achieve an EQE approaching 19%13. In 2024, further enhancement was realized by Ba et al., who introduced gradient-alloyed CdSe/CdZnS CQWs, achieving LEDs with up to 22% EQE14. Most recently, Zeng et al. reported core/crown/shell CdSe/CdSeS/CdZnS nanoplatelets exhibiting 100% PLQY and exceptional thermal stability, enabling LEDs with a record EQE exceeding 30%15. The state-of-the-art EQE of CQW-based LEDs is progressing by leaps and bounds.

Despite impressive advances in EQEs, a major challenge persists in improving the performance of CQW-based LEDs is the low proportion of horizontally aligned TDMs. The TDMs critically determine the photon emission characteristics of semiconductors so that play a key role in enabling the high theoretical EQE of CQW-based LEDs. The orientation of the TDMs depends on the alignment of the CQWs within films16. However, the characteristics of the fixed TDMs in CQW films have not been fully exploited, and a significant gap remains between the current efficiency of CQW-based LEDs and their theoretical limit. The orientation of the TDMs with respect to the device’s electrode interface is particularly important for maximizing outcoupling efficiency and is therefore a key factor in improving LED performance. In general, horizontally oriented TDMs favor efficient light extraction, whereas vertically oriented TDMs lead to energy losses and lower device efficiency17. Currently, CQW films for LED devices are prepared by spin-coating. For spin coating, as the droplet spreads radially outward from the center, the centrifugal force increases proportionally with the radial distance from the rotation axis. This results in a dense accumulation of CQWs at the films center and voids near the films edges. Although inkjet printing involves direct droplet deposition of colloidal nanocrystal solutions onto the substrate surface to form films layer-by-layer, this method tends to induce a coffee-ring effect, leading to central voids and edge accumulation18,19. Both approaches above tend to cause a random distribution of CQWs, failing to achieve a high proportion of horizontally aligned TDMs. Recently, several strategies have been developed to improve horizontal alignment. Combining interfacial ligand engineering with controlled self-assembly, CQW films with record horizontal dipole ratios of 92% and 95% were successfully fabricated, enabling efficient light outcoupling and achieving device performances with EQEs of 18.1% and 26.9% (Supplementary Table 1), respectively20,21. Although these methods have successfully achieved precise control of dipole orientation in CQW films, challenges persist in extending such control to large areas, scaling up device fabrication, and cost efficiency.

In this work, we devise a two-phase driving flat arrangement (TDFA) strategy by utilizing Langmuir-Schaefer technology to create compact, ordered-aligned CQW films. The CQW solution dissolved in chloroform forms a uniform film on the ethylene glycol sub-phase. Van der Waals (VDW) interactions between the CQW ligands and sub-phase molecules, together with the stronger facet-dependent interactions of the wide surfaces, promote the horizontal alignment of CQWs on the sub-phase, while the interfacial driving force between the two phases further induces their compact packing. Subsequently, the film is transferred onto a hole-transport-layer-coated substrate via the horizontal dipping method, yielding a densely packed, horizontally aligned CQW film. This achieves an in-plane TDMs ratio of approximately 90%, leading to a high light extraction efficiency of 35.8%. The resulting CQW-based LEDs show a high EQE of 25.5% and a maximum luminance of 59,620 cd m−2. Additionally, at a luminance of 100 cd m−2, the device demonstrates a T95 operational lifetime exceeding 16,233 hours, showcasing exceptional stability. The scalable fabrication process enables the production of large-area, uniform photoluminescent films, highlighting its potential for practical applications. Notably, the TDFA technique also demonstrates scalable fabrication capabilities, which enables LEDs with a 4 cm2 active area to maintain a luminance of over 60,000 cd m−2.

Results
Fabrication and formation mechanism of CQW films
The CQW films fabricated via the spin-coating process served as the control sample in this work. The liquid spreading process is predominantly governed by centrifugal force in the spin-coating (Fig. 1a), whereas the combined effects of viscous forces, surface tension, and air resistance significantly influence the spreading dynamics and films formation22–26. As the liquid droplets propagate radially outward from the center, the centrifugal force increases linearly with radial distance, creating a shear gradient that drives CQWs toward the substrate edges, resulting in central aggregation and edge depletion. Thus, this phenomenon leads to non-uniform films morphology characterized by a thicker central region and progressively thinner edges. Consequently, the CQWs deposited on the substrate by spin-coating exhibit random distribution, with dense stacking at the center and voids near the edges of the films.

To address the limitations of spin-coating (uneven thickness and random CQWs distribution), we devised the TDFA process as shown in Fig. 1b. The CQWs solution (CQWs dissolved in chlorobenzene solvent) is firstly deposited onto an ethylene glycol subphase. The spreading behavior is primarily governed by surface tension and viscous drag. Then the liquids with lower surface tension tend to spread over those with higher surface tension. Thus, the diffusion occurs at a constant linear rate, enabling the formation of a uniform thickness films27. The TDFA process remains remarkably resilient to minor temperature fluctuations; even when the subphase temperature is elevated to 30°C, the compact, horizontally aligned arrangement of CQWs within the film is preserved without discernible disruption (Supplementary Fig. 1). When CQWs approach the ethylene glycol subphase, VDW interactions emerge between the oleic acid chains (surface ligands of CQWs) and the ethylene glycol molecules. The strength of these interactions depends on crystallographic facets: the wider facets exhibit stronger interactions due to their larger contact area and higher density of interaction sites, while the narrower facets show weaker interactions owing to limited molecular contact points28. These facet-dependent VDW interactions promote the horizontal alignment of CQWs on the sub-phase. Meanwhile, the compact packing of CQW films arises from differences in solvent vapor pressure. Specifically, the contrast in saturated vapor pressures between the two phases generates distinct driving forces for film formation: chloroform favors the formation of compact, horizontally stacked films, whereas solvents with either higher or lower vapor pressures (e.g., n-heptane, octane, n-hexane) disrupt this stacking (Supplementary Figs. 2, 3, and Supplementary Table 1). Consequently, during the spreading of the CQWs solution on the subphase, the wider facets preferentially adhere to the ethylene glycol interface, driving the formation of compact and a horizontally aligned CQW films with improved uniformity.

Characterization and morphology of the CQW films
To validate this assembly mechanism, the characterization and morphology of the CQW films have been studied. Transmission electron microscopy (TEM) characterization (Fig. 2a, b and Supplementary Fig. 4) reveals a random and uneven CQWs distribution in the control film, contrasting sharply with the flat, compact structure of the TDFA film. The TDFA film exhibits a compact film morphology, with the CQWs demonstrating an almost completely horizontal alignment (Fig. 2b). The average spacing of these CQWs is more compact, smaller than that of the control CQWs film. The small particles in the TEM images may stem from byproducts or secondary nucleation and can be reduced by purification (Supplementary Fig. 5)29,30. Photoluminescence (PL) mapping further highlights this disparity: the control film exhibits localized bright spots (yellow circles in Supplementary Fig. 6a) caused by CQWs aggregation, while the TDFA film shows uniform emission (Supplementary Fig. 6b)31. Statistical analysis of the PL intensity distribution (Fig. 2c, d) reveals a narrower intensity spread in the TDFA film, with a coefficient of variation (CV) of 5.7% extreme lower than that of the control film (31%). The CV is defined as the standard deviation-to-mean ratio, representing the relative dispersion of the data. Thus, this result demonstrates the excellent flatness for the TDFA film.

Atomic Force Microscopy (AFM) measurements corroborate these findings, demonstrating a root-mean-square roughness (Rrms) of 0.79 nm for the TDFA film, significantly lower than the 3.37 nm observed for the control film (Fig. 2e, f). The AFM-Amplitude results exhibit the same trend as the height data, which indirectly confirms the consistency of the Height measurements (Fig. 2g, h). The small difference in roughness between the two samples can be attributed to the fact that AFM provides only a relative indication of orientation trends, rather than a direct measurement of the CQW long-axis length.

The cross-sectional scanning transmission electron microscopy–high-angle annular dark-field (STEM-HAADF) image of the control and TDFA samples are shown in Supplementary Fig. 7a, Supplementary Fig. 7b, respectively. The results indicate that the control sample exhibits a CQWs layer thickness of approximately 16 nm, with randomly oriented CQWs and noticeable voids. In contrast, the TDFA sample forms a predominantly horizontally aligned structure with an average thickness of about 9 nm, demonstrating a compact, pore-free film and a significant improvement in the horizontal alignment of CQWs. Furthermore, AFM measurements of the film thickness for both control and TDFA samples corroborate that the measured CQWs layer thickness matches well with the cross-sectional observations (Supplementary Fig. 8). The above results are as expected, the perfectly flat, compact, neatly arranged horizontal CQW films have been achieved by TDFA strategy, displaying great potential for optoelectronic devices.

Colloidal quantum well orientation of the films
Although the TDFA film exhibits a compact and horizontally aligned arrangement of CQWs, the ratio of horizontal TDMs remains unverified. To address this, we employed grazing-incidence wide-angle X-ray scattering (GIWAXS) to investigate the orientation of the CQWs. GIWAXS enables precise analysis of crystal plane alignment on film surfaces32. By combining the X-ray diffraction (XRD) data (Supplementary Fig. 9) with Bragg’s law, we identified three distinct diffraction rings corresponding to the (111), (220), and (311) crystal planes, from the innermost to the outermost rings (Fig. 3a, b). It is well known that diffraction rings appearing as discrete spots indicate a preferred orientation of specific crystal planes within the film. The GIWAXS results show that, compared to the TDFA film, the control film exhibits brighter diffraction spots on the (111) and (311) rings, suggesting a higher degree of preferential orientation along these planes. In contrast, the TDFA film demonstrates weaker diffraction intensity in these directions33. Since the (111) plane typically represents the strongest diffraction peak in zinc blende-structured CQWs—and the (111) and (311) planes correspond to the side and edge facets of the CQWs—their presence is indicative of vertical or tilted orientations. Notably, the GIWAXS patterns for both films exhibit weak diffraction spots for the (111) and (311) planes, while the (220) plane shows strong, continuous diffraction intensity. This implies that the (220) facet, rather than the (111) or (311), is predominantly oriented parallel to the substrate, indicating that most CQWs are horizontally aligned34. Compared to the control film, the TDFA film exhibits a reduction in the (111) and (311) signals, which indirectly suggests fewer vertically oriented CQWs and a tendency toward enhanced horizontal alignment. Since GIWAXS reflects crystal lattice orientations rather than the macroscopic platelet arrangement, it provides only indirect evidence of CQWs alignment. Therefore, we employed polarization-resolved PL and back focal plane (BFP) analysis to further substantiate this orientation trend.

In addition, polarization holography reveals distinct differences in CQW alignment between the control and TDFA films (Supplementary Fig. 10). The control sample (blue curve) exhibits pronounced intensity variations across different polarization angles, indicating strong polarization-dependent behavior consistent with the presence of vertically oriented CQWs. The degree of polarization (DOP), defined as DOP=(Imax−Imin)/(Imax+Imin)16,35,36, is 0.353 for the control sample, while the TDFA film shows a significantly lower DOP of 0.196. This suggests that the spin-coating process induces random geometric distributions of CQWs, with a notable fraction adopting near-perpendicular orientations relative to the substrate. These vertically aligned CQWs contribute to diverse in-plane dipole orientations, thereby enhancing optical anisotropy and polarization sensitivity. In contrast, the TDFA sample (red curve) exhibits a smooth and uniform angular response, indicating consistent light intensity across polarization angles. This reduced polarization dependence implies a predominant in-plane alignment of CQWs parallel to the substrate surface, resulting in more isotropic photon emission. These results further confirm the effectiveness of the TDFA process in controlling film orientation and promoting horizontal alignment of CQWs.

The orientation of transition dipole moments (TDMs) in the CQW films was investigated using back focal plane (BFP) imaging. Local excitation with a 405 nm laser was applied to probe microscale regions of the films. The resulting BFP patterns and corresponding p-polarized line-cut profiles are shown in Fig. 3c. A key signature of in-plane oriented dipoles is the attenuation of p-polarized emission near kx=k0, where kx represents the in-plane wave vector and k0 the wave vector in free space16. Distinct optical characteristics were observed between the control and TDFA-treated films. The control sample exhibited a discernible p-polarized intensity around kx/k0 = 1, whereas the TDFA film displayed nearly no emission in this region. In contrast, for s-polarized emission at ky/k0 = 1, both films showed measurable signals, but the TDFA film exhibited markedly stronger intensity. The degree of horizontal dipole alignment was quantified by the horizontal dipole ratio, Θ=p∥/(p∥+p⊥), where p∥ and p⊥ denote the in-plane and out-of-plane contributions of the optical TDMs, respectively37,38. Fitting the experimental data (Fig. 3d) yielded Θ≈62% for the control film and Θ≈90% for the TDFA treated film, confirming a pronounced enhancement in horizontal alignment16,39. These findings reveal that light emission from the TDFA film originates predominantly from horizontally oriented CQWs. Moreover, multilayer structures fabricated via sequential TDFA deposition (two- and three-layer films) retained strong in-plane orientation (> 85%), demonstrating the robustness of this approach for constructing highly ordered CQW assemblies through a layer-by-layer process (Supplementary Fig. 11).

Simulation of light extraction of CQW-based LEDs
To validate the enhanced light extraction enabled by high-horizontal-TDM films, we conducted finite-difference time-domain (FDTD) simulations40. Using layer-specific parameters (Supplementary Fig. 12), we modeled the outcoupling mechanism in the CQW-based LEDs (Supplementary Fig. 13). The schematic illustrates the light outcoupling mechanisms in the CQW-based LEDs under control and TDFA configurations. For the control device (left image), the photons emitted from the CQWs layer propagate through the device’s multilayer structure (e.g., ZnMgO and Al layers). The random orientation of horizontal TDMs within the CQWs causes emitted photons to undergo multiple internal reflections and scattering events, disrupting their propagation paths and resulting in suboptimal light extraction. In contrast, the TDFA device (right panel) features a well-ordered horizontal TDMs orientation induced by the TDFA process. This alignment enhances in-plane dipole–photon coupling and minimizes parasitic reflections and scattering losses. As a result, photons are more efficiently directed through the ZnMgO and Al layers, leading to significantly improved outcoupling efficiency.

To investigate the wavelength-dependent optical behavior of horizontally oriented dipoles across the visible spectrum, we employed two complementary simulation methods: the Dipole Power method and the Box method (Fig. 4a). The Dipole Power method calculates the radiation characteristics of an individual dipole emitter, making it well-suited for localized sources under simplified boundary conditions. In contrast, the Box method accounts for complex optical architectures with strict boundary constraints, enabling comprehensive modeling of system-wide phenomena such as photon propagation, scattering, and absorption41,42. The strong agreement between the two methods confirms the accuracy of our boundary condition parameterization and validates the reliability of the simulations. As shown in Fig. 4a, the simulated dipole power exhibits a monotonic decline with increasing wavelength, attributed to enhanced surface plasmon-polariton (SPP) resonance effects at shorter wavelengths (λ<50 nm)43. This trend aligns with the spectral dependence of metal-dielectric interfacial modes in multilayer optoelectronic systems. The simulated wavelength-resolved outcoupling efficiency (ηout), presented in Fig. 4b, indicates an efficiency of approximately 37.9% in the red spectral region (621 nm). The light-coupling efficiency varies significantly with wavelength, primarily because the physical mechanisms governing light–matter interactions are inherently highly wavelength-dependent44,45. Additionally, the simulated angular radiation profile (Fig. 4c) exhibits a Lambertian emission pattern, as evidenced by the symmetric intensity distribution about θ=0° (the optical axis)—a hallmark characteristic of ideal Lambertian emitters. Based on the measured horizontal dipole orientation ratios of 62% for the control configuration and 90% for the TDFA configuration, optical outcoupling simulations were conducted (Fig. 4d, e). The control configuration yielded a maximum ηout of 24.4%. In contrast, the TDFA configuration achieved a significantly higher ηout of 35.8% (Fig. 4f), primarily attributed to reduced optical losses stemming from improved dipole alignment and the suppression of interfacial SPP modes. The reduced ηout observed at CQW-to-electrode distances d>50 nm is attributed to increased propagation losses and enhanced optical absorption within the device’s constituent materials46. The EQE of the LEDs is equal to the product of internal quantum efficiency (IQE) and ηout. The higher ηout, the more internally generated photons can be efficiently extracted to the external environment, reducing optical losses and enhancing light output. This directly enhances the EQE of the LEDs.

Performance of CQW-based LEDs
We fabricated CQW-based LEDs and evaluated the angular variation of electroluminescence (EL) intensity for both the control and TDFA devices. Both devices exhibited Lambertian emission patterns, although the EL intensity curve of the TDFA device was slightly lower than that of the control (Fig. 5a). This discrepancy may be attributed to subtle differences in the alignment of the CQWs, which can modulate the angular distribution of EL. The Commission Internationale de l’Éclairage (CIE) coordinates of the EL peak is (0.675, 0.321), which is close to the Rec. 2020 standard for pure red emission (0.708, 0.292) (Supplementary Fig. 14). Figure 5b shows the normalized EL spectra, revealing no significant differences in peak positions or intensities between the two devices, thereby confirming that the TDFA preserves the original EL characteristics. Figure 5c presents the current density (J)–voltage (V)–luminance (L) characteristics. In the low-voltage regime (red box), the control device exhibited a significant leakage current, which was absent in the TDFA device. This is due to the uneven CQWs distribution and voids in the control film, whereas the horizontal alignment and compact morphology in the TDFA film suppress defect-mediated leakage current47,48, The TDFA device in the conducting region exhibits higher current density, which can be attributed to its relatively thinner, pinhole-free emissive layer that enhances charge transport pathways, allowing greater current flow at the same applied voltage49. As the voltage increased, the TDFA device rapidly reached peak luminance, demonstrating low-voltage, high-luminance performance that is advantageous for operational longevity. The current–voltage (J–V) characteristics of the single-carrier devices indicate that, compared to the control, the TDFA devices exhibit more balanced electron and hole density profiles under the same bias conditions. This balanced current density of electrons and holes suggests a potential advantage for device performance optimization and enhanced operational stability (Supplementary Fig. 15)50. The TDFA device achieved 25.5% peak EQE and 59,620 cd m−2 maximum luminance, surpassing the control device (19.83% EQE, 39,880 cd m−2) (Fig. 5d). Considering that the photoluminescence quantum yield (PLQY) of the TDFA film is 72%, this suggests that the ηout of the TDFA device is 35.5%, which is in good agreement with our theoretical simulations (Fig. 4).

To systematically evaluate the reproducibility of the TDFA process, we performed a statistical analysis of EQE measurements across 30 independently fabricated devices. As shown in Fig. 5e, the efficiency histogram exhibits a distribution with a mean value of 23.8%, confirming the exceptional process consistency of our approach. Device stability was assessed under accelerated aging conditions (initial luminance = 10,605 cd m−2) by continuously monitoring the luminance decay. The degradation kinetics were analyzed using the empirical relationship (L0)n × T95 = constant, where L₀ denotes initial luminance and n represents the acceleration factor51; in this case, n was approximately 1.88. Based on the measured T95 @10,000 cd m−2 ≈ 152 minutes (Fig. 5f), the extrapolated T95 @1,000 cd m−2 exceeds 214 hours and the extrapolated T95 @100 cd m−2 exceeds 16,233 hours, demonstrating the longest operational stability reported so far in CQW-based LEDs that reaches commercially viable levels52.

The TDFA method enables uniform large-area film formation while reducing solution consumption by 90% compared to the conventional spin-coating process, which typically requires excessive amounts of CQWs and results in non-uniform film morphology (Supplementary Fig. 16). To further demonstrate the scalability of the TDFA process, we fabricated a 10 × 10 cm2 large-area CQWs film (Fig. 5g). The resulting film exhibited a highly uniform morphology without the edge coverage deficiencies commonly observed in conventional methods, thereby validating the technical feasibility of TDFA for scalable LED manufacturing. Furthermore, we successfully fabricated large-area CQW-based LEDs with dimensions of 2 × 2 cm2, achieving luminance levels exceeding 60,000 cd m−2 (Fig. 5h, Supplementary Fig. 17). Compared to small-area devices, the reduction of EQE in large-area devices may arise from increased series resistance, a higher probability of defects, inadequate thermal management, non-ideal charge transport, size-dependent optical outcoupling and cavity effects, among other factors53–56. The large-area device at turn-on voltage under low luminance illustrate the uniform emission, verifying the feasibility of the TDFA for large-scale manufacture of CQW-based LEDs. (Supplementary Fig. 18). This scalability highlights the strong potential of the TDFA process for industrial-scale LED production.

Methods
Materials
The poly (3,4-ethylene dioxythiophene) / poly (styrene sulfonate) (PEDOT:PSS) was purchased from Xi’an Polymer Light Technology Corp, poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) (PF8CZ) was purchased from Polymer Light Technology Inc. Sodium tetradecanoate (99.99%), Cadmium nitrate tetrahydrate (99.99%), Cadmium acetate dihydrate (99.99%), Selenium powder (99.99%), Anhydrous cadmium acetate (99.99%), Zinc acetate (99.99%), Oleamine (90%), 1-Octadecylene (90%), Octanethiol (99.99%), Methanol (99.99%), Ethanol (99%), N-hexane (99.99%) and Methyl acetate (99.99%) were purchased from Aladin. Oleic acid (90%) was purchased from Sigma Aldrich. Ethylene glycol (99%), chlorobenzene (99.).

Syntheses of colloidal quantum wells
Cadmium myristate (567 mg, 1 mmol), selenium powder (24 mg, 0.5 mmol), and octadecene (50 mL) are placed into a 100 mL three-necked flask. After three argon–vacuum exchange cycles, the mixture is degassed at 100°C for 1 h. The temperature is then elevated to 200°C, at which point a methanolic solution of cadmium acetate monohydrate is injected once the solution turns orange. The reaction is maintained at 240°C for approximately 0.2 h, after which 1 mL of oleic acid is added while cooling to room temperature. For purification, the crude product is washed sequentially with hexane and methyl acetate, centrifuged at 8,000 rpm for 0.083 h, redispersed in hexane, and centrifuged again at 10,000 rpm for 0.017 h. The optical absorption spectrum is subsequently recorded using a UV–Vis spectrophotometer to determine the position of the first excitonic absorption peak. A colloidal CdSe CQW dispersion (1 mL, optical density=30 at the first excitonic transition), cadmium acetate anhydrous (23 mg, 0.1 mmol), zinc acetate anhydrous (73 mg, 0.4 mmol), oleic acid (1 mL), and octadecene (10 mL) are loaded into a 50 mL three-necked flask. The mixture is degassed at 100°C for 0.2 h, after which 0.5 mL of oleylamine is swiftly introduced. The temperature is then raised to 300°C. Octanethiol is introduced continuously at a rate of 1.5 mmol h-1 when the reaction temperature reaches 180°C, and the rate is adjusted to 0.78 mmol h-1 once the temperature increases to 240°C. After the entire amount of octanethiol is delivered, the reaction is maintained at 300°C for an additional 0.5 h before cooling to ambient temperature naturally.

Synthesis of ZnMgO nanoparticles
Zn0.875Mg0.125O nanoparticles were synthesized through a solution-phase precipitation method. Initially, a precursor solution containing precisely controlled stoichiometric ratios of zinc acetate dihydrate (Zn(OAc)2·2H2O, 5.25 mmol) and magnesium acetate tetrahydrate (Mg(OAc)2·4H2O, 0.75 mmol) in anhydrous dimethyl sulfoxide (60 mL) was prepared. This was subsequently mixed with a separately formulated ethanol solution (20 mL) of tetramethylammonium hydroxide pentahydrate (TMAH, 10 mmol) under ambient conditions with continuous magnetic stirring for 1 hour. The resultant colloidal suspension underwent thorough purification via centrifugal separation (6000 rpm, 10 min cycles) with ethanol/acetone (3:1) to remove ionic byproducts, ultimately yielding monodispersed Zn0.875Mg0.125O nanoparticles stabilized in ethanol medium.

Control device fabrication
The device structure consists of indium tin oxide (ITO) glass / PEDOT:PSS / PF8CZ / CQWs / ZnMgO / aluminum (Al). The CQW-LED was fabricated on an ITO-coated glass substrate with a sheet resistance of approximately 20 Ω sq−1. The ITO substrate was sequentially cleaned via ultrasonication in deionized water (15 min), acetone (15 min), and ethanol (15 min), followed by ultraviolet (UV) ozone treatment for 15 min to enhance its work function. A layer of PEDOT:PSS (AI4083) was spin-coated onto the substrate at 5000 rpm and annealed at 140°C for 15 min. The ITO/PEDOT substrate was then transferred into a nitrogen glovebox, where a PF8CZ layer was spin-coated at 3000 rpm (12 mg ml−1 in chlorobenzene) and annealed at 150°C for 30 min. Subsequently, the CQW layer was spin-coated at 3000 rpm (30 mg ml−1 in octane) and annealed at 90°C for 10 min. A ZnMgO layer was then spin-coated at 2000 rpm (30 mg ml−1 in ethanol) and annealed at 60°C for 30 min. Finally, the sample was loaded into a custom-built high-vacuum deposition chamber to thermally evaporate a 100 nm thick aluminum cathode, defining a 4 mm diameter active emission area.

Two-phase driving flat arrangement device fabrication
The device structure consists of indium tin oxide (ITO) glass / PEDOT:PSS / PF8CZ / CQWs / ZnMgO / aluminum (Al). The CQW-LED was fabricated on an ITO-coated glass substrate with a sheet resistance of approximately 20 Ω sq−1. The ITO substrate was sequentially cleaned via ultrasonication in deionized water (15 min), acetone (15 min), and ethanol (15 min), followed by ultraviolet (UV) ozone treatment for 15 min to enhance its work function. A layer of PEDOT:PSS (AI4083) was spin-coated onto the substrate at 5,000 rpm and annealed at 140°C for 15 min. The ITO/PEDOT substrate was transferred into a nitrogen glovebox, where a PF8CZ layer was spin-coated at 3,000 rpm (12 mg ml−1 in chlorobenzene) and annealed at 150°C for 30 min. For the CQW layer deposition, an ethylene glycol subphase solution was first poured into a horizontal solution trough. Drop an appropriate concentration of CQW chloroform solution into the ethylene glycol subphase to form a horizontally oriented CQW film. The ITO/PEDOT/PF8CZ substrate was carefully immersed into the trough, and the CQW film was transferred onto the substrate via the two-phase driving flat arrangement (TDFA) method. Subsequently, a ZnMgO layer was spin-coated at 2000 rpm (30 mg ml−1 in ethanol) and annealed at 60°C for 30 min. Finally, the sample was loaded into a custom-built high vacuum deposition chamber to thermally evaporate a 100 nm thick aluminum cathode, defining a 4 mm diameter active emission area.

CQW-LEDs characterizations
The structural characteristics of the CQWs were investigated using a JEOL JEM−2010 transmission electron microscope, operated at 200 kV. This instrument provides high-resolution imaging capabilities, essential for detailed morphological analysis. Crystallographic analysis of the CQWs was performed using a Bruker D8 Advance diffractometer. This system is designed for comprehensive X-ray diffraction applications, including phase identification and microstructure analysis. Current density–voltage–luminance (J–V–L) measurements were conducted with a Keithley 2400 source meter and a Keithley 6485 picoammeter, coupled with a Si photodetector (Newport 818-UV). Luminance calibration was achieved using a Minolta CS-100 Chroma Meter under ambient conditions. Electroluminescence (EL) spectra were recorded employing an Ocean Optics USB4000 spectrometer in conjunction with the Keithley 2400 power supply.

PL mapping measurement
The fluorescence images of single particles were measured using the 40× objective lens with N.A. of 0.95, which was built on the laser scanning confocal microscope (Nikon A1, inverted microscope). The excitation wavelength was 405 nm.

Polarization degree measurement
The measurement was performed using a fluorescence spectrometer (F-380). The prepared thin film samples were placed in the sample holder, and a polarizer was inserted between the fluorescence spectrometer and the sample holder. The fluorescence spectral intensity was recorded, after which the polarizer was rotated to different angles and the fluorescence intensity was measured accordingly.

Back focal plane imaging measurement
BFP imaging was employed to map the angular distribution of emitted light. A 405 nm continuous-wave laser was used to excite photoluminescence in a nanosheet/coverslip/oil trilayer structure. Emission was collected via a high-NA oil-immersion objective (UPlanSApo 100×, NA 1.44). The objective’s back focal plane was projected onto a Princeton Instruments HRS-300 imaging spectrograph through a 50 mm lens system, enabling polarization-resolved detection to differentiate in-plane and out-of-plane dipole orientations.

GIWAXS measurement
GIWAXS measurements were performed at the SAXS beamline of the Xeuss 2.0 system (Xenocs, France). The collected data were analyzed using SGTools to extract structural information of the CQWs in thin-film configurations.

Refractive index measurement
The refractive index of films in CQW-LED was measured by an ellipsometer (HORIBA France SAS Spectroscopic Ellipsometer, Eceshi Company).

TDFD computation
In this study, we employed finite-difference time-domain (FDTD) simulations to investigate the photonic propagation characteristics of cascade quantum well (CQW)-based devices.

Data availability
All data supporting the findings of this study are available within the paper and its Supplementary files. Any additional information related to the study is available from the corresponding author upon request. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this study, Ba et al. detailed a two-phase driving flat arrangement (TDFA) strategy integrated with Langmuir-Blodgett technology, which allows for the creation of a colloidal quantum well (CQW) film boasting a remarkable 90% horizontal alignment of transition dipole moments (TDMs). This method has significantly elevated the performance of CQW-based electroluminescent diodes (CQW-LEDs), resulting in a light extraction efficiency of 35.8%, an external quantum efficiency (EQE) of 25.5%, and a commendable operational stability with a T95 lifetime surpassing 12,000 hours. Furthermore, this work demonstrated scientific value through the fundamental control of alignment and practical potential via scalable fabrication processes (100 cm² films) and the successful demonstration of large-area LEDs (4 cm²). These findings mark a significant advancement in the application and development of CQW-LEDs. The manuscript is well-structured and presents interesting and compelling results. However, to further enhance the quality of this work, the authors should address the following issues.\n1. The authors showed that the TDFA process enables horizontal alignment and uniform distribution of CQWs through a diffusion mechanism mainly involving surface tension and van der Waals (vdW) interactions. However, since temperature changes in the ethylene glycol subphase can influence the surface tension coefficient, how is the temperature stability of the subphase managed during experiments? And what is its impact? This is a critical factor influencing TDMs and orientation. Please explain this.\n2. Figure 2e, f shows that the AFM-measured heights of Control and TDFA samples are 0.79 nm and 3.37 nm, respectively. However, given that the CQWs possess lengths exceeding 10 nm, a theoretical height discrepancy of 7-8 nm is expected between vertically oriented and horizontally aligned CQWs. This is quite different from the results of the test. What is the reason？\n3. As shown in the GIWAXS results, considering the difference between the randomly oriented CQW in the control and the TDFA films, why is it that the difference in the results isn't very pronounced? It is difference for the nanoplates and crystal orientations. The GIWAXS is usually study the crystal orientation rather than nanocrystals arrangement. Please clarify this.\n4. The simulation results showed higher optical coupling in the short-wavelength region and lower light coupling in the long-wavelength region (Figure 4b). Why does such a significant difference occur for the same structural configuration?\n5. In the supporting documents/supplemental information, the author didn’t provide a detailed procedure for the measurement of the polarization degree performed on the film shown in Figure S5a. Please supplement this information.\n6. Typically, a lower current density at the same voltage would be more favorable for the device. However, compared to the control device, the TDFA device exhibits a higher current density at the same voltage. This is abnormal compared to quantum dots based LEDs. What causes this difference?", "reviewer_2": "This manuscript reports the development of highly efficient and stable colloidal quantum well (CQW) light-emitting diodes (LEDs) using a two-phase driving flat arrangement (TDFA) strategy in combination with Langmuir–Blodgett technology. The authors demonstrate, through both experimental results and simulations, that the TDFA strategy facilitates the horizontal alignment of transition dipole moments (TDMs) in CQW films, thereby significantly enhancing light extraction and external quantum efficiency (EQE). The reported devices achieve a notable EQE of 25.5% and a T₉₅ operational lifetime exceeding 12,000 hours. These results are both impressive and promising for the development of high-performance CQW-based LEDs. The following issues should be addressed before considering for publication in Nature Communications:\n1. The authors argue that the observed flat orientation results in a \"dense\" film morphology. However, this claim lacks reasons and in-depth analysis. The authors should provide additional evidence—such as packing density analysis, cross-sectional imaging—to support this assertion.\n2. Some small particles are visible in the electron microscopy image (Figure 2a). The authors should clarify what these particles are, and how they relate to the formation of the block-like QWs. Further discussion on their origin and potential impact on film quality or device performance would be helpful.\n3. The AFM images in Fig. 2 lacks scale bars. Also, the roughness metric should be reported as Rrms (root-mean-square roughness), rather than Rq.\n4. The bright spots in Figure S2a are attributed to QW aggregation. The authors should provide additional evidence, such as photoluminescence mapping, TEM imaging.\n5. The thickness values of each layer used in the ellipsometry model are not provided. These parameters should be included either in the figure caption or within the main text to enable reproducibility and proper interpretation of the data.\n6. The large-area devices exhibit relatively high turn-on voltages and low efficiencies. Could the authors comment on the potential causes of this performance drop and whether any strategies have been considered to further optimize the performance at larger scales?", "reviewer_3": "The manuscript titled \"Horizontally oriented compact colloidal quantum well films enable efficient and stable electroluminescent diodes\" by Ba et al. introduced a two-phase driving flat arrangement (TDFA) combined with Langmuir–Blodgett deposition to fabricate horizontally aligned colloidal quantum well (CQW) films. They report an improved external quantum efficiency (EQE) and operational stability compared to conventional spin-coated films. While the results presented are scientifically interesting, but in its current form, it is not suitable for publication in Nature Communications.\n1.A major shortcoming of this manuscript in its current form is the lack of comparison to recently published state-of-the-art methods achieving horizontally aligned CQW films. Specifically, recent approaches demonstrated in Advanced Materials (DOI: 10.1002/adma.202305382) and Small (DOI: 10.1002/smll.202206582) have shown equal or superior horizontal dipole alignment, higher or comparable EQE, and excellent stability. Without explicitly benchmarking the TDFA approach against these prior methods, it remains unclear whether the reported method represents a true advancement. The authors must introduce and explicitly discuss recent literature on horizontally aligned CQWs. A detailed comparison highlighting clear advantages (if any) of the TDFA method over these prior approaches regarding film quality, performance, scalability, or reproducibility is required. Without such comparisons, the novelty and significance of this manuscript are insufficient for publication in Nature Communications.\n2.The manuscript implies multilayer stacking capability, yet no explicit experimental evidence was provided to confirm actual multilayer deposition (e.g., cross-sectional imaging or thickness measurements). If multilayer capability is claimed as an advantage over prior monolayer methods, experimental proof is essential.\n3.The schematic provided (Figure 1) is insufficiently detailed to illustrate how the dense and horizontally aligned CQW film is formed in the TDFA process clearly.\n4.Based on the provided methodology, the described approach aligns more closely with the Langmuir–Schaefer method (horizontal transfer) rather than the Langmuir–Blodgett method (vertical transfer).\n5.AFM morphology of CQW films should be included in the main Figure 2."}, "author_response": "Response Letter to Reviewers’ Comments\nReviewer #1 (Remarks to the Author):\nIn this study, Ba et al. detailed a two-phase driving flat arrangement (TDFA) strategy\nintegrated with Langmuir-Blodgett technology, which allows for the creation of a colloidal\nquantum well (CQW) film boasting a remarkable 90% horizontal alignment of transition\ndipole moments (TDMs). This method has significantly elevated the performance of CQW-\nbased electroluminescent diodes (CQW-LEDs), resulting in a light extraction efficiency of\n35.8%, an external quantum efficiency (EQE) of 25.5%, and a commendable operational\nstability with a T95 lifetime surpassing 12,000 hours. Furthermore, this work demonstrated\nscientific value through the fundamental control of alignment and practical potential via\nscalable fabrication processes (100 cm² films) and the successful demonstration of large-\narea LEDs (4 cm²). These findings mark a significant advancement in the application and\ndevelopment of CQW-LEDs. The manuscript is well-structured and presents interesting and\ncompelling results. However, to further enhance the quality of this work, the authors should\naddress the following issues.\nReply: Thank you so much for your positive comments and constructive suggestions.\nComment 1. The authors showed that the TDFA process enables horizontal alignment and\nuniform distribution of CQWs through a diffusion mechanism mainly involving surface\ntension and van der Waals (vdW) interactions. However, since temperature changes in the\nethylene glycol subphase can influence the surface tension coefficient, how is the\ntemperature stability of the subphase managed during experiments? And what is its impact?\nThis is a critical factor influencing TDMs and orientation. Please explain this.\nReply: We thank the reviewer for pointing out the important role of temperature in\ndetermining the surface tension of the ethylene glycol subphase. In our experiments, the\ntemperature of the subphase was carefully controlled by performing the deposition in a\ntemperature-stabilized laboratory environment (22–25 °C, fluctuations <0.5 °C). Ethylene\nglycol has a relatively high specific heat capacity, which minimizes short-term temperature\nvariations during the TDFA process (Reference: Journal of Chemical & Engineering Data,\n40, 611-614 (1995)). To further evaluate the impact, we intentionally controlled the ambient\ntemperature within a relatively broad range (up to 30 °C) and prepared films for TEM and\nback focal plane imaging analysis. The results showed that the horizontal transition dipole\nmoment (TDM) ratio and film morphology remained nearly unchanged (variation < 3%),\nindicating that the nanoplates maintained their flat-lying orientation and that such moderate\nheating did not alter their horizontal alignment. This indicates that the TDFA process is\nrobust against minor thermal fluctuations under our experimental conditions. We also\nemphasize that while extreme temperature variations could in principle influence the\nalignment process by altering the balance between surface tension and van der Waals\ninteractions, under practical laboratory conditions the process is stable and reproducible.\nWe have now clarified these details in the revised manuscript (Page 5 and Extended Data\nFig.1).\nExtended Data Fig.1. a TEM images of TDFA films prepared at 30 °C. b BFP image of\nTDFA CQWs film (30℃). c P-polarized line cut (white line) along the dashed line in of the\nBFP image.\nThe TDFA process is highly resistant to minor temperature fluctuations, as increasing the\nsubphase temperature to 30 °C did not significantly affect the compact horizontal\narrangement of CQWs in the film (Extended Data Fig. 1).\nComment 2. Figure 2e, f shows that the AFM-measured heights of Control and TDFA\nsamples are 0.79 nm and 3.37 nm, respectively. However, given that the CQWs possess\nlengths exceeding 10 nm, a theoretical height discrepancy of 7-8 nm is expected between\nvertically oriented and horizontally aligned CQWs. This is quite different from the results\nof the test. What is the reason?\nReply: We agree that a single, perfectly vertical versus perfectly horizontal CQW would\ntheoretically yield a height difference close to the CQW long axis dimension (≈10 nm).\nHowever, in practical films, several factors reduce the apparent AFM-measured height\ndifference: (i) Partial Orientation Distribution – The CQWs are not exclusively vertical or\nhorizontal; rather, they exhibit a statistical distribution of tilt angles. This leads to an\neffective average film thickness smaller than the geometric long-axis length. (ii) Multilayer\nPacking and Interdigitation – In both control and TDFA films, CQWs partially overlap, stack,\nor interdigitate, which decreases the step height recorded by AFM. (iii) Surface Roughness\nand Tip Convolution Effects – AFM measures the topography convoluted with tip geometry\nand local surface roughness, which often underestimates the true particle height, especially\nfor soft organic/inorganic hybrid films. (iv) Ligand Layer Compression – Organic ligands\non CQW surfaces can compress during film formation, further lowering the apparent AFM\nthickness. As a result, the absolute values of 0.79 nm and 3.37 nm should be understood as\neffective average heights rather than the exact physical dimensions of isolated CQWs.\nImportantly, the clear relative increase in height from the control to the TDFA sample is\nfully consistent with enhanced horizontal alignment.\nWe have clarified this point in the revised manuscript (Page 7), emphasizing that AFM\nprovides a relative indicator of orientation trends rather than a direct measurement of the\nCQW long-axis length.\nThe small difference in roughness between the two samples can be attributed to the fact that\nAFM provides only a relative indication of orientation trends, rather than a direct\nmeasurement of the CQW long-axis length.\nComment 3. As shown in the GIWAXS results, considering the difference between the\nrandomly oriented CQW in the control and the TDFA films, why is it that the difference in\nthe results isn't very pronounced? It is difference for the nanoplates and crystal orientations.\nThe GIWAXS is usually study the crystal orientation rather than nanocrystals arrangement.\nPlease clarify this.\nReply: In our case, the observed changes in the relative intensity distribution along the in-\nplane vs. out-of-plane directions are consistent with improved horizontal alignment in the\nTDFA films. The shape orientation of CdSe nanoplatelets is strongly correlated with their\ncrystal lattice orientation. Consequently, the alignment of nanoplatelets can be inferred from\nGIWAXS measurements. Since GIWAXS can penetrate the upper layers of nanoplates and\nprobe the lattice orientations of those underneath, horizontally oriented nanoplates may also\ncontribute signals from their side facets. As a result, the measurement reflects the statistical\ndistribution of lattice orientations across the entire film rather than only the surface\narrangement, which explains why the overall differences are not very pronounced. However,\nwe fully agree that GIWAXS reflects crystal lattice orientation rather than the macroscopic\nplatelet arrangement, thus only provides indirect evidence for the CQW alignment.\nTo clarify this, we have revised the manuscript (Page 9) to explicitly state that\nGIWAXS is complementary to other characterization methods. The alignment trend is\nfurther corroborated by BFP analysis and polarization-resolved PL, which together provide\na more complete picture of the horizontal orientation induced by TDFA.\nSince GIWAXS reflects crystal lattice orientations rather than the macroscopic platelet\narrangement, it provides only indirect evidence of CQW alignment. Therefore, we\nemployed polarization-resolved PL and back focal plane (BFP) analysis to further\nsubstantiate this orientation trend.\nComment 4. The simulation results showed higher optical coupling in the short-wavelength\nregion and lower light coupling in the long-wavelength region (Figure 4b). Why does such\na significant difference occur for the same structural configuration?\nReply: This phenomenon is usually observed in nanophotonic structures. Even when the\nstructural configuration is fixed, the core reason for the wavelength-dependent variation in\nlight-coupling efficiency lies in the fact that the key physical mechanisms governing light–\nmatter interaction exhibit strong wavelength dependence (references are listed below): (i)\nScale effects—at shorter wavelengths (small λ), the characteristic dimensions of the\nstructure more effectively modulate the optical field (e.g., via localized enhancement),\nwhereas at longer wavelengths (large λ), light tends to “bypass” the structure, leading to\nreduced coupling efficiency; (ii) Phase matching—efficient coupling requires the in-plane\nwavevector component of the incident light to precisely match the propagation constant of\nthe target mode (β_mode), but the waveguide dispersion of β_mode means that this\ncondition is satisfied only at certain wavelengths, with longer wavelengths prone to\nmismatch; (iii) Resonant enhancement—effective only near the intrinsic resonant\nwavelength of the structure (typically in the short-wavelength regime); (iv) Material\ndispersion—for example, the pronounced increase in Ohmic loss in metals at longer\nwavelengths; and (v) Radiative losses—the weaker confinement of long-wavelength modes\nfurther suppresses coupling efficiency. Therefore, the contrast between high coupling\nefficiency at shorter wavelengths and its sharp decline in the longer-wavelength regime, as\nshown in Fig. 4b, is an inevitable outcome of the combined effects of scale, matching,\nresonance, and loss mechanisms.\nReferences:\n[1]. William L. Barnes et al. Surface plasmon subwavelength optics. Nature 424, 824-\n830 (2003).\n[2]. Kerry J. Vahala. Optical microcavities. Nature 424, 839–846 (2003).\nWe have added a brief explanation in the revised manuscript to clarify this point. (Page\n12,13).\nThe light-coupling efficiency varies significantly with wavelength, primarily because the\nphysical mechanisms governing light–matter interactions are inherently highly wavelength-\ndependent 44,45.\nComment 5. In the supporting documents/supplemental information, the author didn’t\nprovide a detailed procedure for the measurement of the polarization degree performed on\nthe film shown in Figure S5a. Please supplement this information.\nReply: Thank you very much for your comment and suggestion. We have added these details\nin the revised Extended Data (Page 2) as following:\nPolarization Degree Measurement\nThe measurement was performed using a fluorescence spectrometer (F-380). The prepared\nthin film samples were placed in the sample holder, and a polarizer was inserted between\nthe fluorescence spectrometer and the sample holder. The fluorescence spectral intensity\nwas recorded, after which the polarizer was rotated to different angles and the fluorescence\nintensity was measured accordingly.\nComment 6. Typically, a lower current density at the same voltage would be more favorable\nfor the device. However, compared to the control device, the TDFA device exhibits a higher\ncurrent density at the same voltage. This is abnormal compared to quantum dots based LEDs.\nWhat causes this difference?\nReply: Typically, a lower current density at the same voltage is considered a positive\nindicator of device optimization. A higher current density at the same voltage is not\ngenerally a standard target for QLED optimization; however, it can be an intermediate result\nof a more aggressive optimization strategy. Its ultimate value depends entirely on the\nexternal quantum efficiency (EQE) performance, in which our case shows a significant\nimprovement.\nWe attribute this difference to the introduction of the TDFA method, which reduces\nvoids within the nanoplate (quantum well, QW) layer. In the device’s off-state region (< 2\nV), these voids may penetrate multiple layers, allowing direct contact between adjacent\ntransport layers and causing leakage current. At the same voltage, this leakage current\nincreases the total current but represents non-radiative current that does not contribute to\nlight emission. In the on-state region (> 2 V), the charge transport pathways are disrupted\nbecause the voids break the continuity of the QW network. This forces carriers to detour or\ntunnel/jump across the voids, increasing the tortuosity of the path and thus the resistance,\nleading to a reduction in current density and total current at the same voltage.\nOverall, TDFA reduces leakage current in the off-state region and improves charge\ncarrier balance after turn-on. Additionally, the TDFA emissive layer is relatively thinner and\ndenser. Therefore, in the on-state region (> 2 V), the TDFA device enhances charge transport\npathways, allowing higher current flow at the same applied voltage.\nWe have now clarified these details in the revised manuscript (Page 14) as following.\nThe TDFA device in the conducting region exhibits higher current density, which can be\nattributed to its relatively thinner, pinhole-free emissive layer that enhances charge transport\npathways, allowing greater current flow at the same applied voltage49.\nReviewer #2 (Remarks to the Author):\nThis manuscript reports the development of highly efficient and stable colloidal quantum\nwell (CQW) light-emitting diodes (LEDs) using a two-phase driving flat arrangement\n(TDFA) strategy in combination with Langmuir–Blodgett technology. The authors\ndemonstrate, through both experimental results and simulations, that the TDFA strategy\nfacilitates the horizontal alignment of transition dipole moments (TDMs) in CQW films,\nthereby significantly enhancing light extraction and external quantum efficiency (EQE). The\nreported devices achieve a notable EQE of 25.5% and a T₉₅ operational lifetime exceeding\n12,000 hours. These results are both impressive and promising for the development of high-\nperformance CQW-based LEDs. The following issues should be addressed before\nconsidering for publication in Nature Communications:\nComment 1. The authors argue that the observed flat orientation results in a \"dense\" film\nmorphology. However, this claim lacks reasons and in-depth analysis. The authors should\nprovide additional evidence—such as packing density analysis, cross-sectional imaging—\nto support this assertion.\nReply: As additional support for our claim, the leakage current analysis presented in Fig. 5\nprovides indirect evidence that the TDFA films would possess a compact morphology\nwithout pinholes. Furthermore, we agree that the statement on the dense morphology of\nhorizontally oriented CQW films requires further clarification. In our revised manuscript,\nwe have added a more detailed discussion of the physical origin of the dense films\nhighlighting the role of interfacial surface tension and solvent vapor pressure during the\nTDFA process. We have included a discussion of cross-sectional TEM characterization in\nthe revised manuscript, which directly confirms that the TDFA films are densely. The\nupdated contents are following.\nMeanwhile, the compact packing of CQW films arises from differences in solvent vapor\npressure. Specifically, the contrast in saturated vapor pressures between the two phases\ngenerates distinct driving forces for film formation: chloroform favors the formation of\ncompact, horizontally stacked films, whereas solvents with either higher or lower vapor\npressures (e.g., n-heptane, octane, n-hexane) disrupt this stacking (Extended Data Fig. 2,\nFig. 3, and Table 2).(Page 6).\nExtended Data Fig.2. TEM images of TDFA films prepared from CQW solutions in octane\nwith different subphases: a acetone, b acetonitrile, c ethylene glycol, and d deionized water.\n(with a size of 200nm)\nExtended Data Fig.3. TEM images of TDFA films prepared on an ethylene glycol subphase\nusing different CQW solvents: a octane, b n-heptane, c chloroform, and d n-hexane. (with\na size of 200nm)\nTo address the reviewer’s concern, we have revised the extended data to explicitly clarify\nthese points and have included supplementary discussion (Extended Data Fig.2 and Fig.3)\nto provide stronger support for the “dense” film morphology claim.\nThe compactness of CQW films can be explained by surface tension and vapor pressure,\nwhich is directly related to Gibbs free energy. The change in Gibbs free energy is given by\n𝛥𝐺\n= (𝛾𝑎 + 𝛾𝑎𝑏)− 𝛾𝑏 (4)\n𝐴\nΔG\nSab = − (5)\nA\nHere, –ΔG represents the decreas\nS\ne𝑎 𝑏in\n=\nG i\nγ\nbb𝑏s\n−\nfr e\nγ\ne𝑎 en\n−\ne r\nγ\ngy𝑎𝑏 of the system; A is the spread(in\n6\ng)\narea; γ is the surface tension of liquid b; γ is the surface tension of liquid a; and γ is the\nb a ab\ninterfacial tension between liquids a and b. When S ≥ 0, liquid a can spontaneously spread\non the surface of liquid b. For efficient film formation, the subphase must have a relatively\nhigh surface tension and low volatility. In our experiments, when octane was used as the\nCQW solvent and ethylene glycol as the subphase, the films became very compact, with\nnanoplates tending to stack vertically. By replacing octane with solvents of higher vapor\npressure (e.g., n-heptane, chloroform, n-hexane), the volatility increased and, in the case of\nchloroform/ethylene glycol, the nanoplates formed dense films but were aligned\nhorizontally. Thus, the dense packing of CQW films arises from the combined effect of the\ninterfacial surface tension balance and the solvent vapor pressure. (Extended Data Page 8,\n9)\nExtended Data Table 2\nSolvent acetone acetonitrile acetonitrile deionized octane n- chloroform n-\nwater heptane hexane\nsurface\ntension 72.8 25 23.5 43.4 21.1 21.6 28.9 18.4\n(mN/m\n20 ℃)\nsaturated\nvapor\npressure 2.3 13.3 24 6.2 1.3 6.0 13.3 17\n(Pa 20 ℃)\nExtended Data Fig.7. Cross-sectional STEM-HAADF images of the films. a Control\nlayer (16 nm) showing a disordered morphology with pinholes. b TDFA layer (9 nm)\nexhibiting a horizontally continuous and pinhole-free structure.\nThe cross-sectional scanning transmission electron microscopy–high-angle annular dark-\nfield (STEM-HAADF) image of the control and TDFA samples are shown in Extended Data\nFig. 7a, 7b, respectively. The results indicate that the control sample exhibits a CQW layer\nthickness of approximately 16 nm, with randomly oriented CQWs and noticeable voids. In\ncontrast, the TDFA sample forms a predominantly horizontally aligned structure with an\naverage thickness of about 9 nm, demonstrating a compact, pore-free film and a significant\nimprovement in the horizontal alignment of CQWs. (Page 7).\nComment 2. Some small particles are visible in the electron microscopy image (Figure 2a).\nThe authors should clarify what these particles are, and how they relate to the formation of\nthe block-like QWs. Further discussion on their origin and potential impact on film quality\nor device performance would be helpful.\nReply: We thank the reviewer for this insightful comment. The small particles visible in\nTEM are most plausibly byproduct quantum dots and/or residual magic-size clusters arising\nfrom secondary nucleation during CdSe nanoplatelet synthesis (References: J. Am. Chem.\nSoc.144, 8096–8105 (2022), Mater. Adv. 2, 1204-1228 (2021)), which can lead to the\nreformation of core quantum dots. These particles are not directly related to the CQWs and\ndifferential centrifugation can remove most of the small particles to a certain extent, and as\nlong as their content is kept at a low level, the impact on the overall film morphology or\ndevice performance can be neglected.\nIn the revised version, we have included the TEM image of the CQWs after particle removal\nin Extended Date. In addition, further discussion has been added in the revised manuscript\n(Page 11) as following.\nThe small particles in the TEM images may stem from byproducts or secondary nucleation\nand can be reduced by purification (Extended Data Fig.5) 29,30.\nExtended Data Fig.5 TEM image of CQWs (scale bar: 50 nm).\nComment 3. The AFM images in Fig. 2 lacks scale bars. Also, the roughness metric should\nbe reported as Rrms (root-mean-square roughness), rather than Rq.\nReply: We have now revised this detail in the manuscript. (Page 6). In the revised\nmanuscript, We have moved the AFMdata to Fig.2，scale bars have been added to the AFM\nimages in Fig.2. for clarity. In addition, the roughness values have been corrected and are\nnow reported as Rrms (root-mean-square roughness) instead of Rq (Page 7).\nAtomic Force Microscopy (AFM) measurements corroborate these findings, demonstrating\na root-mean-square roughness (Rrms) of 0.79 nm for the TDFA film, significantly lower\nthan the 3.37 nm observed for the control film (Fig. 2e, 2f). The AFM-Amplitude results\nexhibit the same trend as the Height data, which indirectly confirms the consistency of the\nHeight measurements (Fig. 2g, 2h)\nFig.2. e AFM topography map of control film. f AFM topography map of TDFA film. g\nAFM-Amplitude of control film. h AFM-Amplitude of TDFA films. (scale bar: 200 nm)\nComment 4. The bright spots in Figure S2a are attributed to QW aggregation. The authors\nshould provide additional evidence, such as photoluminescence mapping, TEM imaging.\nReply: The bright spots observed in Extended Data Fig.6 is indeed attributed to local CQW\naggregation. Our previous TEM imaging (Extended Data Fig.4) also shows stacked regions\nin the control sample. Furthermore, this has been corroborated by prior studies, which\nconfirm that bright regions in the film arise from quantum dot aggregation, indicating areas\nof higher CQW density (Reference: Adv. Optical Mater. 13, 2500058 (2025)). We have\nrevised the manuscript to include this reference. (Page 7)\nPhotoluminescence (PL) mapping further highlights this disparity: the control film exhibits\nlocalized bright spots (yellow circles in Extended Data Fig. 6a) caused by CQW aggregation,\nwhile the TDFA film shows uniform emission (Extended Data Fig. 6b)31.\nComment 5. The thickness values of each layer used in the ellipsometry model are not\nprovided. These parameters should be included either in the figure caption or within the\nmain text to enable reproducibility and proper interpretation of the data.\nReply: The thickness values of each layer used in the ellipsometry model have now been\nincluded in the revised Extended Data (either in the relevant figure caption) to ensure\nreproducibility and proper interpretation of the data (Extended Data Page 18 and Extended\nData Fig.12)\nExtended Data Fig.12. Device structure diagram the light outcoupling mechanisms based\non a the control and b TDFA CQWs\nThe schematic illustrates the light outcoupling mechanisms in CQW-based devices under\ncontrol and TDFA configurations: control （left image）: Photons emitted from the CQW\nlayer propagate through the device’s multilayer structure (e.g., ITO 65 nm, PEDOT:PSS 20\nnm, PF8CZ 30 nm, Control CQWs 20 nm, TDFA CQWs 10 nm, ZnMgO 35 nm, Al 100 nm\nlayers).\nComment 6. The large-area devices exhibit relatively high turn-on voltages and low\nefficiencies. Could the authors comment on the potential causes of this performance drop\nand whether any strategies have been considered to further optimize the performance at\nlarger scales?\nReply: The relatively high turn-on voltages and lower efficiencies observed in the large-\narea devices are mainly attributed to increased series resistance and non-uniformities in film\nthickness and morphology across the larger substrate area. These factors can hinder charge\ninjection and transport, thereby reducing overall efficiency. To address this, we are\nconsidering several optimization strategies, such as reducing series resistance by optimizing\nelectrode design, and further engineering the charge transport layers. We believe these\nefforts will help minimize the performance gap between small- and large-area devices. We\nrecently remanufactured large-area LEDs by replacing the large-area ITO substrates,\nadjusting the substrate resistance, and modifying the processing parameters of the transport\nlayers, thereby reducing the turn-on voltage to 2.9 V and achieving a luminance exceeding\n60,000 cd·m⁻² (Page 15).\nExtended Data Fig.16. a. The Current density(J)-Voltage-Luminance curves of the LEDs\nbased large-area QWs film prepared by TDFA. b. The EQE- Luminance-Current efficiency\ncurves of the LEDs based large-area QWs film prepared by TDFA.\nFurthermore, we successfully fabricated large-area CQW--based LEDs with dimensions of\n2 × 2 cm, achieving luminance levels exceeding 60,000 cd·m-2 (Fig. 5h, Extended Data Fig.\n16). This scalability highlights the strong potential of the TDFA process for industrial-scale\nLED production.\nReviewer #3 (Remarks to the Author):\nThe manuscript titled \"Horizontally oriented compact colloidal quantum well films enable\nefficient and stable electroluminescent diodes\" by Ba et al. introduced a two-phase driving\nflat arrangement (TDFA) combined with Langmuir–Blodgett deposition to fabricate\nhorizontally aligned colloidal quantum well (CQW) films. They report an improved external\nquantum efficiency (EQE) and operational stability compared to conventional spin-coated\nfilms. While the results presented are scientifically interesting, but in its current form, it is\nnot suitable for publication in Nature Communications.\nReply: Thank you very much for your comments.\nComment 1. A major shortcoming of this manuscript in its current form is the lack of\ncomparison to recently published state-of-the-art methods achieving horizontally aligned\nCQW films. Specifically, recent approaches demonstrated in Advanced Materials (DOI:\n10.1002/adma.202305382) and Small (DOI: 10.1002/smll.202206582) have shown equal\nor superior horizontal dipole alignment, higher or comparable EQE, and excellent stability.\nWithout explicitly benchmarking the TDFA approach against these prior methods, it remains\nunclear whether the reported method represents a true advancement. The authors must\nintroduce and explicitly discuss recent literature on horizontally aligned CQWs. A detailed\ncomparison highlighting clear advantages (if any) of the TDFA method over these prior\napproaches regarding film quality, performance, scalability, or reproducibility is required.\nWithout such comparisons, the novelty and significance of this manuscript are insufficient\nfor publication in Nature Communications.\nReply: We appreciate the reviewer’s suggestion. This method has made true advancement\nfor the fabrication of CQW based LEDs as following:\nFor the fabrication of large-area CQW thin films, achieving highly horizontally oriented\nTDMs is relatively straightforward, which offers significant advantages over conventional\nmethods such as spin-coating. Furthermore, common approaches rely on self-assembly to\nachieve high TDMs and thus high device performance. Here, we demonstrate a novel\nmethod that attains both high TDMs and excellent device performance, while also offering\nadvantages for the fabrication of large-area films, enabling the successful production of\nlarge-area devices.\nA previously reported work (Advanced Materials (DOI: 10.1002/adma.202305382) and\nSmall (DOI: 10.1002/smll.202206582)) demonstrated remarkable progress by designing a\nspin-coating-assisted self-assembly strategy to obtain highly oriented TDMs and efficient\nCQW-LEDs, thereby overcoming the traditional orientation limitations of spin coating.\nHowever, when it comes to preparing large-area films with high orientation, the spin-coating\nprocess still suffers from inherent drawbacks—most notably its poor scalability, which\nmakes it unsuitable for uniform large-area deposition. For instance, as shown in the 10 cm\n× 10 cm film in our work (Fig. 5, Extended Data Fig.15), the TDFA method readily produces\nhighly horizontally oriented TDM films, whereas spin coating cannot achieve such complete\ncoverage.\nIn comparison, techniques such as inkjet printing and drop-casting can indeed produce\nlarge-area films, but the orientation of CQWs cannot be precisely controlled using these\nmethods. Therefore, whether by spin coating, inkjet printing, or drop-casting, it remains\nvery challenging to simultaneously achieve both large area and high orientation. More\nimportantly, spin coating suffers from extremely low material utilization, typically only\n1~5%. In contrast, the theoretical material utilization of our TDFA method can reach up to\n90%. This advantage is particularly critical for expensive materials such as CQWs, as it\nsignificantly reduces cost and provides a viable approach for future industrialization. We\nalso successfully fabricated large-area LEDs using TDFA method, achieving a luminance\nof over 60,000 cd/m2, which demonstrates the potential of TDFA for large-area LED\napplications.\nFig. 5g Large-area CQW films fabricated via TDFA method: photograph under UV\nillumination (10 × 10 cm) (left). Extended Data Fig.15 Large-area film prepared by spin\ncoating technology: photograph under UV illumination (10 × 10 cm) (right).\nIn summary, our method demonstrates clear superiority in terms of orientation control,\nlarge-area film fabrication, material utilization, and cost-effectiveness, thereby highlighting\nits strong potential and advanced nature.\nWe compared the parameters of LEDs achieving high TDMs using different methods and\nsummarized them in Table 1.\nExtended Data Table 1\nIn-plane EQE L Device Preparation\nmax(nm) References\nTDMs (%) (%) (cd/m2) stability (h) process\n𝜆\n518 84 23.6 - - Spin-coating Sci. Adv.\nsitu grown (2021)4\n528 75 24.96 - (T @100 Spin-coating Nat.\n50\ncd/m2) 2.3 Self-Assembled Commun.\n(2022)5\n644 92 18.1 19,800 （T @100 Spin-coating Small (2023)6\n95\ncd/m2）247 self-assembled\nmonolayer\n(SAM)\n646 95 26.9 55,754 (T @100 Spin-coating Adv. Mater.\n95\ncd/m2）over self-assembled (2023)7\nmonolayer\n15,000\n(SAM)\n622 90 25.5 59,620 （T @100 TDFA This work\n95\ncd/m2）over\n16,233\nIn addition, we updated the device lifetime. Tested at an initial luminance of 10,605 cd·m⁻²,\nthe T₉₅ lifetime reached 152 min. The degradation kinetics were analyzed using the\nempirical relationship (L₀) × T = constant, where L₀ denotes initial luminance and n\n95\n𝑛\nrepresents the acceleration factor, the lifetime at 1,000 cd·m⁻² is 215 h, and at 100 cd·m⁻² it\nreaches 16,233 h, indicating that our TDFA method exhibits excellent stability.\nWe have revised the Introduction and Discussion sections (Page 4 and Extended Data Table\n1) to explicitly introduce these references, compare the methods, and highlight the practical\nadvantages of TDFA, thereby emphasizing the novelty and significance of our approach.\nRecently, several strategies have been developed to improve horizontal alignment.\nCombining interfacial ligand engineering with controlled self-assembly20,21, CQW films\nwith record horizontal dipole ratios of 92% and 95% were successfully fabricated, enabling\nefficient light outcoupling and achieving device performances with EQEs of 18.1% and 26.9%\n(Extended Data Table 2), respectively. Although these methods have successfully achieved\nprecise control of dipole orientation in CQW films，challenges persist in extending such\ncontrol to large areas, scaling up device fabrication, and cost efficiency.\nComment 2. The manuscript implies multilayer stacking capability, yet no explicit\nexperimental evidence was provided to confirm actual multilayer deposition (e.g., cross-\nsectional imaging or thickness measurements). If multilayer capability is claimed as an\nadvantage over prior monolayer methods, experimental proof is essential.\nReply: We thank the reviewer for this comment. We would like to clarify that our manuscript\ndoes not directly benchmark TDFA against previously reported monolayer self-assembly\nmethods. Instead, our comparison focuses on spin-coated control samples, which do not\nyield true monolayers but rather randomly oriented, porous CQW layers (~16 nm, confirmed\nby cross-sectional TEM and AFM). In contrast, the TDFA sample forms a predominantly\nhorizontally aligned structure with an average thickness of about 9 nm, demonstrating a\ndense, pore-free film and a significant improvement in the horizontal alignment of CQWs.\nThese results, now included in the revised manuscript (Extended Data Fig.7and Extended\nData Fig.8.), highlight the advantages of TDFA over conventional spin-coating. We agree\nthat a direct performance comparison with state-of-the-art monolayer approaches would be\nvaluable, but it lies beyond the scope of the present work. In the revised manuscript, we\nhave removed wording that may imply multilayer stacking, as our work does not focus on\nmultilayer deposition or its comparison with monolayer self-assembly methods.\nExtended Data Fig.7 Cross-sectional STEM-HAADF images of the films. a Control layer\n(16 nm) showing a disordered morphology with pinholes. b TDFA layer (9 nm) exhibiting\na horizontally continuous and pinhole-free structure.\nExtended Data Fig.8.a AFM 3D height image of the control film. b AFM 3D height image\nof the TDFA film. c AFM height profile of the control film (ΔH ≈ 17 nm). d AFM height\nprofile of the TDFA film (ΔH ≈ 8 nm).\nWe have added the relevant discussion in the main text (Page7).\nThe cross-sectional scanning transmission electron microscopy–high-angle annular dark-\nfield (STEM-HAADF) image of the control and TDFA samples are shown in Extended Data\nFig. 7a, b, respectively. The results indicate that the control sample exhibits a CQW layer\nthickness of approximately 16 nm, with randomly oriented CQWs and noticeable voids. In\ncontrast, the TDFA sample forms a predominantly horizontally aligned structure with an\naverage thickness of about 9 nm, demonstrating a compact, pore-free film and a significant\nimprovement in the horizontal alignment of CQWs. Furthermore, AFM measurements of\nthe film thickness for both control and TDFA samples corroborate that the measured CQW\nlayer thickness matches well with the cross-sectional observations (Extended Data Fig.8).\nComment 3. The schematic provided (Figure 1) is insufficiently detailed to illustrate how\nthe dense and horizontally aligned CQW film is formed in the TDFA process clearly.\nReply: We thank the reviewer for this valuable suggestion. To provide a clearer\nunderstanding of the TDFA process, we have revised Fig.1 to include additional details\nillustrating the formation of dense, horizontally aligned CQW films. This updated schematic\nbetter conveys the process and the resulting CQW orientation.\nFig. 1 Illustration of CQW films fabrication.a Spin-coating process. b TDFA process.\nComment 4. Based on the provided methodology, the described approach aligns more\nclosely with the Langmuir–Schaefer method (horizontal transfer) rather than the Langmuir–\nBlodgett method (vertical transfer).\nReply: We thank the reviewer for pointing this out. We have carefully revised the manuscript\nto clarify that our approach follows the Langmuir–Schaefer method (horizontal transfer)\nrather than the Langmuir–Blodgett method. All relevant text, including the schematic and\nmethod description, has been updated accordingly to accurately reflect the horizontal\ntransfer mechanism used in the TDFA process (Page 1, Page 4).\nIn this work, we utilized a two-phase driving flat arrangement (TDFA) strategy combined\nwith Langmuir–Schaefer method technology to create a compact CQWs film exhibiting\npredominantly horizontal TDMs orientation. (Page 1)\nIn this work, we devised a two-phase driving flat arrangement (TDFA) strategy by utilizing\nLangmuir- Schaefer technology to create a compact ordered ordered-aligned CQW films.\n(Page 4)\nComment 5. AFM morphology of CQW films should be included in the main Figure 2.\nReply: We thank the reviewer for this helpful suggestion. The AFM morphology of the\nCQW films has now been included in the main Fig.2 as recommended. We have updated\nthe main text (Fig. 2 caption and relevant discussion) to clearly reference these AFM data,\nallowing readers to assess CQW film morphology and roughness. (Page 7)\nAtomic Force Microscopy (AFM) measurements corroborate these findings, demonstrating\na root-mean-square roughness (Rrms) of 0.79 nm for the TDFA film, significantly lower\nthan the 3.37 nm observed for the control film (Fig. 2e, 2f). The AFM-Amplitude results\nexhibit the same trend as the Height data, which indirectly confirms the consistency of the\nHeight measurements (Fig. 2g, 2h)"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The quality of the revised ms has been improved. I now recommend acceptance of this work.", "reviewer_2": "In the response letter and the revised manuscript, the authors have addressed my concerns. I therefore suggest accept of this work.", "reviewer_3": "The manuscript has been significantly improved through the authors’ revision. The technical novelty of the TDFA approach and its scalability have been convincingly demonstrated. Nevertheless, I recommend minor revision before acceptance to further clarify two key points that will strengthen the manuscript.\n1. Large-area device performance and uniformity (related to Fig. 5h):\nThe manuscript should clearly specify the active area of the device whose characteristics are shown in Fig. 5. Otherwise, readers may mistakenly assume that the performance corresponds to the 2 × 2 cm device shown in Fig. 5h. Since the actual EQE and performance data for the 2 × 2 cm device are only presented in Extended Data Fig. 16, this distinction should be explicitly mentioned in the main text. Furthermore, the authors should briefly discuss why the EQE of large-area devices is lower compared to small-area devices. This clarification will provide valuable insight into the scalability challenge.\nRegarding Fig. 5h, the photograph was taken under bright emission conditions, which makes it difficult to assess the luminance uniformity across the device. If possible, a photograph at lower luminance should be provided, or at least the authors should comment that such an image would better illustrate the uniform emission enabled by their technique.\n2. Multilayer stacking capability:\nIn the original submission, the phrase “allowing for layer-by-layer stacking to form horizontally compact CQW films” was included, but it has now been deleted. I understand that the present work focuses on single-layer compact films and demonstrates clear advantages compared to spin-coating. However, since the Langmuir–Blodgett and Langmuir–Schaefer methods are generally known to be capable of multilayer stacking, readers will naturally wonder whether the TDFA strategy can also achieve multilayers while maintaining horizontal alignment. It would greatly enhance the impact of the manuscript if the authors could provide preliminary results of multilayer stacking with the TDFA method."}, "author_response": "Response Letter to Reviewers’ Comments\nReviewer #3 (Remarks to the Author):\nThe manuscript has been significantly improved through the authors’ revision. The\ntechnical novelty of the TDFA approach and its scalability have been convincingly\ndemonstrated. Nevertheless, I recommend minor revision before acceptance to further\nclarify two key points that will strengthen the manuscript.\nReply: We thank you so much for your positive comments and constructive suggestions.\nWe have revised the manuscript and supplemented experimental evidences based on\nyour suggestions.\nComment 1. Large-area device performance and uniformity (related to Fig. 5h): The\nmanuscript should clearly specify the active area of the device whose characteristics\nare shown in Fig. 5. Otherwise, readers may mistakenly assume that the performance\ncorresponds to the 2 × 2 cm device shown in Fig. 5h. Since the actual EQE and\nperformance data for the 2 × 2 cm device are only presented in Extended Data Fig. 16,\nthis distinction should be explicitly mentioned in the main text. Furthermore, the\nauthors should briefly discuss why the EQE of large-area devices is lower compared to\nsmall-area devices. This clarification will provide valuable insight into the scalability\nchallenge. Regarding Fig. 5h, the photograph was taken under bright emission\nconditions, which makes it difficult to assess the luminance uniformity across the\ndevice. If possible, a photograph at lower luminance should be provided, or at least the\nauthors should comment that such an image would better illustrate the uniform emission\nenabled by their technique.\nReply: We thank the reviewer for this helpful suggestion. We have revised the\nmanuscript by adding a photograph of the device in its operating state in Fig. 5d and\nindicating the effective area size in the title. Furthermore, the main text clearly specifies\nthe effective area of the device corresponding to the features shown in Fig. 5 (2 × 2\nmm²). In addition, the main text already indicated that the performance data of the 2 ×\n2 cm² device are provided in Extended Data Fig. 18. We agree with the reviewer that a\nbrief discussion of the performance difference between small-area and large-area\ndevices would be valuable. We have added a short explanation in the revised manuscript\n(Page 15). Specifically, the reduction in EQE in large-area devices is mainly due to (i)\nincreased series resistance and voltage drop across the larger electrode area, (ii) a higher\nprobability of defects/pinholes/short circuits with increasing area, (iii) poor thermal\nmanagement, including localized heating and uneven power density distribution, (iv)\nnon-idealities in charge injection/transport layers at large scales, and (v) variations in\noptical outcoupling and cavity effects with device size and encapsulation. We\nemphasize that this reflects a common scalability challenge in QLEDs and other thin-\nfilm optoelectronic devices.\nFig. 5d EQE-L characteristics of the devices. The inset shows the device in operation\nwith an emission area of 2 × 2 mm².\nWe have now clarified these details in the revised manuscript as following.\nThe TDFA device achieved 25.5% peak EQE and 59,620 cd·m-2 maximum luminance,\nsurpassing the control device (19.83% EQE, 39,880 cd·m-2) (Fig. 5d). (Page 13)\nWe appreciate the reviewer’s careful observation (Fig. 5h). To address this, we have\nprovided additional images of the same LED device operating at different luminance\nlevels (Extended Data Fig. 19). As shown, at turn-on voltage under low luminance, the\nlarge-area film exhibits overall uniform emission, although brighter edges can be\nobserved. This effect mainly arises from preferential current conduction at the device\nedges and the voltage drop in the central region, with additional contributions from\noptical leakage caused by cavity and waveguiding effects. Upon increasing the applied\nvoltage (Fig. 5h), the device demonstrates a uniform emission state at high luminance.\nIn the revised manuscript, we have added a sentence explaining that the intense\nemission makes it difficult to visually assess luminance uniformity in the presented\nimages. To provide a clearer demonstration, we have also included photographs of the\nsame 2 × 2 cm² device under lower luminance conditions (Extended Data Fig. 18),\nwhich better illustrate the uniform emission achieved by our fabrication process.\nExtended Data Fig.18. Large-area CQW-based LEDs fabricated via TDFA method:\noperational-state photograph (2 × 2 cm²) (emission at turn-on voltage -low luminance).\nFig.5h Large-area CQW-based LEDs fabricated via TDFA method: operational-state\nphotograph (2 × 2 cm²) (high luminance).\nThe manuscript was revised as following:\nFurthermore, we successfully fabricated large-area CQW-based LEDs with dimensions\nof 2 × 2 cm², achieving luminance levels exceeding 60,000 cd·m-2 (Fig. 5h, Extended\nData Fig. 17). Compared to small-area devices, the reduction of EQE in large-area\ndevices may arise from increased series resistance, a higher probability of defects,\ninadequate thermal management, non-ideal charge transport, size-dependent optical\noutcoupling and cavity effects, among other factors53-56. The large-area device at turn-\non voltage under low luminance illustrate the uniform emission, verifying the feasibility\nof the TDFA for large-scale manufacture of CQW-based LEDs. (Extended Data Fig. 18)\n(Page 15)\nComment 2. Multilayer stacking capability: In the original submission, the phrase\n“allowing for layer-by-layer stacking to form horizontally compact CQW films” was\nincluded, but it has now been deleted. I understand that the present work focuses on\nsingle-layer compact films and demonstrates clear advantages compared to spin-\ncoating. However, since the Langmuir–Blodgett and Langmuir–Schaefer methods are\ngenerally known to be capable of multilayer stacking, readers will naturally wonder\nwhether the TDFA strategy can also achieve multilayers while maintaining horizontal\nalignment. It would greatly enhance the impact of the manuscript if the authors could\nprovide preliminary results of multilayer stacking with the TDFA method.\nReply: We thank the reviewer for raising this important point. In fact, the TDFA\nstrategy can be extended to multilayer stacking while maintaining in-plane alignment.\nWe have carried out preliminary experiments, in which two- and three-layers structured\nCQW films were successfully deposited using sequential TDFA processing. The\nresulting films exhibited well-aligned horizontal dipole orientation, demonstrating the\nfeasibility of applying the TDFA method to achieve multilayer structures with high\nhorizontal TDMs orientation (>85%).\nExtended Data Fig.11. a BFP image of 2-layer CQWs film (left) and 3-layer CQWs\nfilm (right). b P-polarized line cut (white line) along the dashed line in of the\nBFP image.\nHowever, the efficiencies of the 2- and 3- layers based LED are lower than that of the\nsingle layer based LED, likely due to the too thicker emissive layer hindering charge\ninjection, causing carrier imbalance and enhanced non-radiative recombination\n(Fig.R1).\nFig. R1a The Current density(J)-Voltage-Luminance curves of the LEDs based 2-layer\n/ 3-layer QWs film prepared by TDFA. b The EQE- Luminance-Current efficiency\ncurves of the LEDs based 2-layer / 3-layer QWs film prepared by TDFA.\nThese results have now been included as a new Extended Data Fig. 11 in the revised\nmanuscript, and the related discussion has been added to the main text.\nFurthermore, 2- and 3-layer CQW films deposited by sequential TDFA also showed\nhigh horizontal TDMs orientation (>85%), demonstrating the feasibility of the TDFA\nmethod for achieving well-aligned horizontal dipole orientation multilayer nanocrystals\nfilm through layer-by-layer process (Extended Data Fig.11). (Page 10)"}, {"round": 3, "reviewer_comments": {"reviewer_3": "This manuscript is now suitable for publication."}, "author_response": ""}]

Decision letter