Scalable fabrication of high-quality perovskite films is critical for the industrialization of perovskite solar cells (PSCs). Meniscus-guided coating is promising, yet the trade-off between maintaining liquid film continuity and securing the time window for crystal growth remains a significant bottleneck. Here, we demonstrate a strategy to achieve both full coverage and giant domains (>3 & times; 10(-2) mm(2)) via reduced-temperature (100 degrees C) bar-coating. By integrating in situ microscopy with fluid dynamics analysis, we reveal that a specific low-speed condition (0.3 mm s(-1)) within the evaporation regime maintains the solution in a metastable supersaturation zone. Our analysis identifies that the circulation loop formed by the interaction of Couette and Marangoni flows not only continuously supplies solute to the meniscus tip but also suppresses excessive evaporation through advective cooling. This fluid-dynamic regulation prevents explosive nucleation while circumventing the film rupture (dewetting) often observed in slow drying, enabling the formation of continuous films with giant crystal domains. Consequently, PSCs utilizing these giant-domain films achieved a power conversion efficiency of 16.5%, significantly outperforming devices with smaller crystal domains. This study provides a physical framework linking macroscopic coating parameters to microscopic crystallization dynamics, offering a rational pathway for scalable, high-performance device manufacturing.

Photoalignment using Berry-phase masks enables single-step transfer of complex liquid crystal (LC) patterns but faces difficulty in reproducing submicrometer patterns. In this study, the physical limitation using Berry-phase masks is elucidated through combined simulations and experiments. Finite-difference time-domain analysis reveals that transmitted light evolves into elliptically polarized states as the mask period decreases, and experimental evaluation confirms that ellipticity significantly weakens anchoring strength. In addition, a multilayer Berry-phase mask design is proposed to suppress polarization ellipticity. This approach clarifies the origin of alignment disorder and advances the mass production of high-resolution LC meta-optics and augmented reality/virtual reality photonic devices.

Ferroelectric nematic liquid crystals (FNLCs) are polar fluids in which spontaneous polarization coexists with nematic orientational order, giving rise to unusual dielectric and electromechanical responses. However, the collective modes underlying their giant dielectric response remain unclear. Here, we show that this response originates from the superposition of two distinct relaxation modes rather than a single process. Dielectric spectroscopy reveals that the low-frequency mode exhibits soft-mode-like behavior associated with short-axis molecular rotation, whereas the high-frequency mode corresponds to a Goldstone-like phase displacement of an effective transverse polarization component rotating around the director. These assignments are supported by systematic analyses of temperature, electric-field, cell-thickness, and alignment-layer dependences. Our results demonstrate that the giant dielectric response of ferroelectric nematics reflects multiple collective polarization dynamics with different symmetries and restoring forces, providing a framework for interpreting dielectric spectra in polar nematic fluids.

Ferroelectric nematic liquid crystals (FNLCs) exhibit strong polarization responses, yet accurate evaluation of their dielectric properties without polarization contribution, that is, soft-mode-like dielectric permittivity, remains challenging because fluctuations of spontaneous polarization can lead to an apparent overestimation of permittivity. Here, we investigate the dielectric response of a DIO-based FNLC material under DC electric fields and show that the soft-mode-like contribution can be isolated once the director is reoriented perpendicular to the substrates. At field strengths sufficient to induce this vertical alignment, the peak dielectric relaxation strength becomes independent of cell thickness, consistent with effective suppression of the polarization-related contributions. Using this approach, we determine the DC-field dependence of the transition temperature to the ferroelectric phase and show that the relationship between the transition temperature and the DC field changes across field-induced intermediate phases, consistent with differences in the symmetry of their molecular alignment. In particular, at high fields, the transition from a nematic-like intermediate phase to a ferroelectric phase exhibits characteristics of a second-order phase transition. These results establish a practical route to extract reliable dielectric properties of FNLCs and provide a basis for quantitative physical characterization of this class of materials.

The orientation behaviour of ferroelectric nematic liquid crystals (FNLCs) is fundamentally different from that of conventional paraelectric NLCs due to the influence of macroscopic polarisation. The orientation of FNLC is strongly influenced by both the alignment film and the processing method. In this study, we examined how two key parameters -pretilt and the fluorophilic/fluorophobic properties of the alignment film- affect FNLC polarisation orientation. Our results demonstrate that these factors consistently impact FNLC behaviour under both the rubbing and photo-alignment methods. We found that the presence of pretilt determines whether the polarisation direction at the substrate interface is uniquely and uniformly fixed. Additionally, we found that altering the fluorophilic or fluorophobic properties of the alignment film reverses the fixed polarisation direction. Furthermore, we achieved a uniform vertical polarisation orientation without requiring an external field, highlighting a new approach to controlling FNLC alignment.

Ferroelectric nematic liquid crystals (FNLCs) are promising soft platforms for nonlinear optics, but quantitative determination of their second-order nonlinear optical coefficients has been hindered by limited alignment control. Here, polarization-resolved second-harmonic generation (SHG) measurements on a uniformly aligned dioxane-based FNLC, combined with Jones-matrix simulations, enable determination of all principal tensor components. The resulting tensor is consistent with the expected C_∞ v and Kleinman symmetries, while the measured coefficients cannot be explained by a simple sum of molecular first hyperpolarizabilities. These results provide a quantitative basis for understanding nonlinear optical responses and guiding the design of FNLC-based nonlinear optical materials and devices.

Ferroelectric nematic liquid crystals (FNLCs) combine fluidity with spontaneous polarization, offering promising avenues for flexible electromechanical systems. Here, we demonstrate that mechano-electrical conversion in FNLCs can be enhanced by mechanically programming a robust macroscopic polarization alignment. Using hybrid liquid crystal cells composed of rigid glass and flexible substrates, we show that deformation in the ferroelectric nematic phase suppresses polarization domains and produces long-range ordered polarization alignment over millimeter-scale areas. This geometry-driven alignment originates from coupling between the FNLC's spontaneous splay deformation and the deformation-imposed cell geometry, and we further find that the selected polarization direction exhibits clear material dependence. Leveraging this deformation-enabled alignment, we develop an FNLC-based energy harvester that converts mechanical deformation into an output of approximately 1 V. These findings establish geometry-driven alignment as a practical design strategy for boosting FNLC mechano-electrical conversion while providing polarization control for soft electronic devices.

π-Conjugated polymers are promising materials for next-generation flexible and lightweight electronics owing to their solution processability and excellent charge transport properties, where molecular orientation is critical for efficient charge transport. However, maintaining high molecular orientation at high coating speeds required for industrial production remains challenging, particularly when using volatile, low-boiling-point solvents. In this study, we employed a cooled, high-speed bar-coating method at 50 mm s-1 to fabricate highly oriented films of poly{2,2'-[(2,5-bis(2-octyldodecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)dithiophene-5,5'-diyl]-alt-thieno[3,2-b]thiophene-2,5-diyl} (PDPP-DTT) from low-boiling-point solvents. For volatile solvents such as chloroform (bp: 61 °C) and trichloroethylene (bp: 87 °C), substrate cooling suppressed rapid solvent evaporation and random crystallite nucleation, enabling highly oriented films. Time-resolved polarized UV-Vis absorption spectroscopy further revealed that molecular orientation develops during the solidification process, suggesting the formation of a lyotropic liquid crystalline phase guided by a weakly oriented template layer. The degree of orientation strongly depended on both solvent volatility and substrate temperature. While cooling was essential for volatile solvents, excessive cooling of less volatile solvents, such as chlorobenzene (bp: 132 °C), resulted in reduced orientation. These results highlight the trade-off between suppressing random nucleation and avoiding orientation relaxation. By balancing solvent volatility with substrate temperature control, this strategy enables scalable, low-temperature fabrication of high-performance polymer films compatible with flexible substrates.

Broadband cholesteric liquid crystal (CLC) reflectors are highly desirable for advanced optical applications, but their polarization behavior under oblique incidence remains underexplored. This study reveals anomalous polarization-selective reflection in broadband pitch-gradient CLCs, including linear polarization selectivity and the reversal of circular polarization handedness under oblique incidence. The pitch-gradient CLC reflects a much wider spectrum than that of a uniform-pitch CLC, covering the full visible range. Under oblique incidence, it exhibits anomalous polarization-selective reflections. Notably, for light incident from the short-pitch (front) side of the element, the reflector preferentially reflects linear polarization of transverse electric (TE) mode over its transverse magnetic (TM) mode and even shows a reversal of circular polarization selectivity at certain angles. When illuminated from the long-pitch (back) side, the device maintains the usual circular polarization preference but splits the broadband reflection band such that TE and TM polarizations dominate different wavelength regions. These phenomena are confirmed by rigorous Berreman 4 x 4 matrix simulations, which replicate the experimental results and indicate that the effects originate from the intrinsic pitch-gradient structure. These findings uncover and elucidate anomalous polarization effects unique to broadband pitch-gradient cholesteric reflectors. The results offer practical design rules for compact broadband polarization control under oblique incidence, particularly for AR display combiners and other polarization-sensitive optical systems.

Introducing passivation molecules has been being considered as one of effective strategies to reduce surface crystal defects and hence improve the performance and stability of perovskite solar cells (PSCs). In this paper, we report the effects of organofluorine molecules, specifically trifluoroacetic acid (TFA), added in the ethyl acetate (EA) anti-solvent on the characteristics of MAPbI3 based PSCs, which are related to interfacial surface states, band bending characteristics and charge extraction processes. Anti-solvents with several volume fractions of TFA were used in the perovskite layer deposition step by the spin-coating technique. The current density vs. voltage (J–V) curve hysteresis was suppressed while the PSC stability and the PSC performance repeatability of the fabrication results were much improved in PSC prepared using EA anti-solvent with moderate volume fraction of TFA (i.e. 5

An electric field-based orientation method for blue phase (BP) liquid crystals (LCs) enables particularly high-quality orientation and determines the BPI orientation by applying an out-of-plane electric field in a planar alignment cell. However, the mechanism, including the role of field-induced phases like BPX in BPI lattice reorientation, remains unclear. This study systematically investigates the role of BPX in BPI reorientation under various electric field conditions and alignment layer characteristics. When an out-of-plane electric field was applied, the [110] axis of BPI aligned in the field direction, and the [001] axis aligned along the easy axis. Under an in-plane electric field, the [110] axis aligned parallel to the field, while the out-of-plane orientation depended on alignment treatments. These results reveal that BPI lattice reorientation is determined by the applied field direction and alignment layer characteristics, even when reorientation is mediated solely through BPX. This research offers insights into the BPI orientation dynamics and introduces a method for achieving precise orientation control with reduced field intensities, enhancing the potential for advanced BPLC device applications.

Electrostriction is present in all dielectrics, but the electrostriction itself is generally minuscule and is even insignificant in low-dielectric-constant materials. Herein, extraordinary electrostriction is found in mesomorphic blue phase (BP) crystals, which are fluidic "giant" crystals with a lattice constant of several hundred nanometers and contain 107-108 molecules in each unit cell. In situ optical observations revealed that the BP crystals exhibit -19.5% to 15.7% electrostrictive actuation at weak field strengths (<3 V/μm), during which a transient monoclinic phase is found. The monoclinic phase occurs in the form of twinning and single crystals successively, which acts as an intermediate state to dominate the pathway of electrostrictive structural transition. Furthermore, we experimentally confirmed that a tensorial crystal-optic effect is induced in BPs by electrostriction, which updates our conventional understanding about liquid crystalline materials that the electro-optics has always been considered as a scalar effect. This work reveals the structural polymorphism in electrostrictive soft crystals, which, in the meantime, provides additional degrees-of-freedom for their advanced applications in nano or micro actuators, flexible electronics, and photonics of next generation, by precisely manipulating the soft crystalline structures and their crystal-optic characteristics.

This study provides design insights for liquid crystal (LC) planar optics by investigating how spatially varying pretilt angles affect LC orientation in the bulk. A cell with homeotropic alignment on one surface and a linear pretilt distribution from 0 degrees to 90 degrees on the opposite surface was analyzed using nematic LC continuum theory. The simulation results revealed that the LC director exhibits splay deformation, in which the strength of deformation corresponds with the pretilt angle. The retardation profile depends on the ratio between the cell thickness and the pretilt pattern period: when the period exceeds 10 times the cell thickness, the retardation profile becomes sufficiently linear, which is crucial for high-efficiency wavefront modulation in diffractive optical elements. This knowledge offers essential design guidelines for compact, tunable, and high-performance LC-based optical devices.

Blue phase polymer-templated ferroelectric nematic liquid crystal (BPPT-FNLC) enables FNLC orientation in BP structures while retaining ferroelectricity. This study investigated their electro-optical properties, revealing a significant enhancement in the Kerr effect in the ferroelectric phase. In the ferroelectric phase, voltage polarity reversal induces rapid molecular reorientation due to polarization reversal, resulting in sub-microsecond birefringence switching. Moreover, under AC voltage, the material exhibits large birefringence modulation (similar to 0.05) at frequencies as high as similar to 100 kHz. These findings establish BPPT-FNLC as a promising material for high-speed and polarized light-independent optical modulation, addressing the needs of advanced optoelectronic applications.

Liquid crystal-based holographic optical elements (LC-based HOEs) have garnered significant attention for their high diffraction efficiency, flexibility, and lightweight nature, making them ideal for applications such as near-eye displays, head-up displays, and beam steering devices. However, conventional LC-based HOEs have issues with pattern deformation and slow recovery when an electric field is applied, and often require additional LC layers or mechanical actuation to achieve effective switching. This study introduces nematic liquid crystal (NLC) nanocomposites that enable electro-optic switching while retaining the original director orientation pattern. The HOE with the NLC nanocomposite maintains high diffraction efficiency even under an applied electric field, with experimental results strongly correlating with theoretical simulations. Moreover, ultrafast response times of less than 100 mu s were achieved. These findings highlight the potential of NLC nanocomposites for developing high performance, compact LC-based HOEs capable of rapid switching, expanding their applications in advanced optical systems such as beam steering.

It is known that the orientation characteristics of ferroelectric nematic liquid crystals (FNLCs) were completely different from those of paraelectric NLCs due to the presence of macroscopic polarization. Moreover, the conventional FNLC orientation is strongly dependent on the alignment film and alignment process. In this study, we focused on two key parameters given by the alignment process: pretilt and the fluorophilic/fluorophobic properties of the alignment film. We clarified that these parameters commonly affect the polarization orientation characteristics of FNLC under both the rubbing method and the photo-alignment method. Furthermore, we successfully achieved uniform vertical polarization orientation without an external field.

Patterned surface conditions designed through self-organization at the environmental interface of soft matter systems, such as liquid crystals (LCs), are critically important for advancing engineering applications. In this study, we develop a fabrication method and experimentally demonstrate adaptive gradient refractive index optics, using by LCs aligned on ultraviolet (UV)-irradiated polyimide films with a programmable pretilt pattern. To verify the Friedel-Creagh-Kmetz (FCK) rule, which states that the pretilt angle of LCs dep-ends on the surface free energy of the substrate, we evaluated the surface free energy of UV-irradiated polyimide films, breaking it down into each component of intermolecular interaction. The results suggest that the polar component of the intermolecular interaction in the alignment layer plays a key role in determining the pretilt angle. We successfully demonstrated the formation of distinct linear and periodic retardation distributions by spatially controlling the UV irradiation time using a slit mask. The linearity of the retardation profile is preserved under the applied voltage. Furthermore, we demonstrated that the transmitted light is deflected by the LC device and that the diffraction angle can be electrically controlled. These results pave the way for the development of electrically tunable flat optics capable of real-time spatial modulation and mechano-free operation.

The triple-cation perovskite Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 was deposited using the hot-bar-coating method. The effects of the substrate temperature and coating bar sweep speed on the film quality were investigated. Coating the precursor solution at a substrate temperature of 150 degrees C, reduced fabrication time by eliminating the post-annealing process, which is essential to conventional film fabrication methods, i.e., the antisolvent method. We further investigated the dependence of thin film thickness and quality on the coating bar sweep speed, finding that the optimal film quality was achieved at a speed of 4 mm/s. Importantly, decomposition into PbI2 was not observed during film fabrication for the triple-cation perovskite. The results of solar cell property measurements, indicating that the fabricated devices maintained high performance for 500 h in ambient air, suggest that the hot-bar-coating method is a promising approach for producing perovskite solar cells with high atmospheric stability and potentially low cost.