Flexible Displays Research Articles

Room-Temperature, Solution-Processed, Robust, Transparent, and Conductive SiOx/AgNW Nanocomposite Coating.

AgNW networks show high promise as a conductive material due to excellent flexibility, low resistance, high transparency, and ease of large-scale preparation. However, the application of AgNW networks has been hindered by their inherent characteristics, such as easy oxidation degradation, chemical corrosion, and structural instability at high temperatures. In this study, a dense SiOx protective layer derived from perhydropolysilazane was introduced to fabricate a robust SiOx/AgNW nanocomposite coating through an all-solution process at room temperature. The achieved nanocomposite coating shows outstanding thermal stability up to 450 °C, resistance to ultraviolet radiation, and excellent mechanical performance by maintaining stability after 10,000 cycles of bending at a radius of 2.5 mm, 1000 cycles of peeling, and 1200 cycles of wearing. Meanwhile, the nanocomposite coating demonstrates exceptional chemical tolerance against HCl, Na2S, and organic solvents. A transparent heater based on the nanocomposite coating achieves a remarkable benchmark with a maximum temperature of 400 °C at 20 V. These features highlight the potential of the nanocomposite coating in flexible electronics, optoelectronics, touch screens, and high-performance heaters.

PEDOT:PSS-based electronic “paper” with high surface-interface and mechanical strength and ultra-long wet-resistant capacity

Organic electrochromic conducting polymers (CPs) are at the forefront of flexible and ultra-thin display electronics. Solution processable poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) exhibits excellent electrical and electrochemical behavior in line with great processability, stability, and other promising properties. However, their uses are limited by the weak mechanical properties, wet instability, as well as inevitable conflicts among different functionalities and structural characteristics, etc. In this study, we designed and fabricated a high-mechanical-strength electronic “paper”, PEDOT:PSS/PEG-UPy film, employed a thermoplastic polyurethane poly(ethylene glycol)-2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (PEG-UPy) using diverse processing (drop coating, spin coating, blade coating and 3D printing) of its “electric ink (E-ink)” from the mechanical mixture of its isopropanol (IPA) solution with aqueous PEDOT:PSS dispersion. Compared to PEDOT:PSS film, the incorporation of supramolecular chain-expanding unit 2-amino-4-hydroxy-6-methylpyrimidine (UPy) into the PEG-UPy molecular backbone resulted into optimized self-supporting (substrate-free) film of PEDOT:PSS/PEG-UPy(10 wt%) which showed great flexibility, enhanced mechanical strength (elongation at break 47.08 %, tensile strength of 19.16 MPa, toughness 7.973 MJ m−3), considerable electrical properties (0.509 S cm−1), desirable physical properties including resistance to abrasion and solvent-wiping, and excellent surface-interface properties (e.g., hardness of 3H, adhesion of level 0, glossiness of 91). Its electrochromic capabilities include an optical contrast (ΔT) value of 67 %, a fast redox reaction (4 s and 3 s, respectively), and a coloring efficiency (722.19 cm2 C−1). Similar to paper, they can be easily tailored or folded into a variety of forms, but have greater advances on dense morphology, flat surface, considerable optical transparency (79.5 %), as well as robust resistance to mechanical damage (in the case of bending, stretching, and folding, etc.), water (immersing > 150 days), and dirt. The combined effect of molecular design of PEG-UPy, abundant hydrogen-bonded cross-linking interaction and “good” solvent effect of IPA to PEDOT:PSS play important roles in this system. This is the first work on solution processable PEDOT:PSS-based electrochromic “paper” being able to meet much comprehensive performance requirements for the application in practical complex working environment.

Silicone-polyurea based clear viscoelastic films for flexible displays, impact of diisocyanate, chain extender, soft segment molecular weight, and hard segment contents

Clear viscoelastic film (CVF), an optically clear type of press sensitive adhesive (PSA), is crucial for bonding different functional layers together in a display module. With the rapid growth of consumer electronics, foldable display devices offer new challenges to CVF, such as optical clarity, low modulus, low glass transition temperature (Tg), good stress-relaxation, good recoverability, and decent adhesion strength. However, there are some contradictories in combining above properties (e.g., good stress-relaxation vs. good recoverability). Silicone polymers can impart softness and prompt elastic recovery over a wide range of temperatures, thereby making their advantageous features suitable for CVF candidates in flexible display devices. In our previous work, an optimum sample of CVF based on low-hard-segment silicone polyurea (LH-SPU) exhibited well-balanced viscoelasticity for flexible displays. In this work, the impact of diisocyanate, chain extender, soft segment molecular weight, and hard segment contents on SPU elastomeric CVFs (SPU CVFs) for flexible displays was further detailly and systematically evaluated. The different components of SPU can be readily adjusted to prepare CVFs with different properties, such as selectable range of modulus (104 ∼ 105 Pa), temperature plateau (−40 ∼ 120 °C), recoverability (78.15 ∼ 90.97 % under 500 % axial strain), creep-resistance (above 85.5 % creep-recoverability under shear stress of 20, 30, 40, 50 KPa), initial adhesive work (0.17 ∼ 2.23 mJ), and 180° peel strength (9.25 ∼ 14.6 N/25 mm after placing 24 h). Furthermore, the SPU CVFs had undergone 200,000 successive folding reliability tests without any cracking or delamination to verify their potentiality in flexible display devices.

Flexible sensor based on conformable, sticky, transparent elastomers for electronic skin

As 5G technology advances and enhances the interconnection of science and technology, the demand for advanced sensors has increased. Conventional rigid sensors are inadequate to meet these new requirements, thus sparking significant interest in flexible sensors. However, taking into account the biocompatibility, skin compliance, sensing performance, mechanical properties and optical properties of flexible sensors is still the direction of efforts. Therefore, in this study, the flexible sensor with a sandwich structure was prepared using AgNWs as a conductive filler and P32-PDMS elastomer as a flexible substrate. The PDMS elastomer is modified by blending PEG-PPG-PEG and PDMS, giving the P32-PDMS elastomer low Young’s modulus (32.35 kPa), high elongation at break (over 450 %) and good adhesion (18.94 N/m), and the P32-PDMS elastomer still retains a certain light transmittance (82.22 %) and biocompatibility (RGR=89.524). These properties simultaneously endow the flexible sensor with good sensitivity (GF=17.27), wide detection range (0–100 % strain), and excellent cycling stability (5000 cycles). When the flexible sensor is used as e-skin to monitor human body movements, stable signals are generated regardless of the low-strain movements of the human body (pulse and sound) or the high-strain movements of the human body (pressing and joint bending). Therefore, the prepared flexible sensor has great potential as e-skin in many fields such as personal health monitoring, human motion detection, human–computer interaction, flexible display, etc.

Surface engineering of Al2O3 dielectric layer for all-sputtered-oxide transparent and flexible a-IGZO thin film transistor

Transparent flexible display devices have attracted massive attention in recent years owing to their practical applications that can be compatibly adapted to human demand and technological development. Worldwide researchers have studied flexible transparent thin film transistors (TFTs) to qualify them for the backplane component of future transparent and flexible displays. Simplifying the fabrication process of a TFT can be considered a critical need for reducing consumed cost, time, toxic chemicals. In this study, sputtering was utilized as a major fabrication method for manufacturing a transparent oxide TFT device, which demonstrated good mechanical flexibility. A simple surface treatment process was applied to enhance the susceptibility of the sputtered Al2O3 dielectric through multiple coatings of solution processed Al2O3. It is noteworthy that the transparent oxide TFT device exhibits a high optical transparency of 81.12% and good electrical switchability at low operating voltage (3 V) with a decent mobility of 4.37 cm2 V−1 s−1 and proven mechanical durability.

Towards the optimal design of optically clear adhesives for flexible display

As device form factors evolve towards increased complexity and flexibility, the role of adhesives within the display module stack becomes increasingly crucial. These adhesives are essential for bonding functional layers with minimal thickness while mitigating stress during the dynamic behavior of flexible devices. This paper offers a comprehensive overview of the essential properties of adhesives - such as adhesion, viscoelasticity, optical characteristics, and environmental reliability - necessary for the stable operation of flexible display devices across diverse form factors and environments. In particular, it provides an in-depth look at ongoing research in simulation, material selection, polymer network control, and the integration of new functionalities to achieve optimal performance. Furthermore, this paper discusses extensive research outcomes addressing the growing demand for sustainable solutions. Building on this knowledge, we highlight the future direction of adhesives for flexible displays.

Ultrathin silica-encapsulated perovskite nanocrystals for high color purity mechanoluminescence

The quest for advanced mechanoluminescence (ML) systems with precise color control and a broad color gamut is pivotal for developing flexible display technologies. Despite significant progress in embedding ML phosphors into elastic polymer matrices to enhance flexibility and resilience, achieving high color purity and a broad color spectrum remains a substantial challenge. This study introduces an innovative approach by incorporating ultrathin silica-encapsulated perovskite nanocrystals (PNCs) into the ML platform, leveraging their exceptional color purity and high photoluminescence quantum yield. Our encapsulation technique, which covers PNCs with SiO2 shells, not only enhances the environmental stability of PNCs but also enables their integration into a polydimethylsiloxane (PDMS)-based ML matrix, thereby forming a robust perovskite mechanoluminescence platform (PMP) film. This strategy significantly improves ML color purity with a full width at half maximum (FWHM) of 32 nm, as well as leading to high ML stability in various harsh conditions such as heating and water immersion. Our findings demonstrate the potential of silica-encapsulated PNCs to transcend the conventional limitations of ML systems, marking a significant stride towards the realization of advanced flexible displays with superior color purity.

Recent Research Advances in Textile-Based Flexible Power Supplies and Displays for Smart Wearable Applications

Recent Research Advances in Textile-Based Flexible Power Supplies and Displays for Smart Wearable Applications

Dietary flexibility of insectivorous bats, Eptesicus fuscus and Myotis lucifugus, during Magicicada spp. Brood X emergence

Emergence of periodical cicadas, Magicicada spp. Davis, 1925, presents an ideal opportunity to study dietary flexibility and selective feeding behavior of bats. It is known that a wide array of taxa prey upon Magicicada spp., but few bat species have been documented to consume them. When larger than typical prey items, such as periodical cicadas, become abundant for a short time frame, insectivorous bats may exhibit alteration in dietary selection that provides insight into capacity and conditions for feeding. Evidence of Magicicada spp. consumption was detected in guano via polymerase chain reaction (PCR) and physical detection in both Eptesicus fuscus (Palisot de Beauvois, 1796) and Myotis lucifugus (Le Conte, 1831), two bat species of different sizes and with different dietary profiles. The consumption of these larger prey items, when they are locally abundant, supports a display of opportunistic behavior and diet flexibility in these two bat species.

Flexible plasmonic display featuring differentiated and localized control over transmission and reflection

Structural colors using metal materials, plasmonic color generation, can confine optical excitation beyond the diffraction limit owing to nanoscale metals with high efficiency in light absorption and scattering. They have several advantages over conventional display technology, including superior resolution and long-term preservation. However, most research on plasmonic color generation has been conducted for the development of static color generation, and dynamic tuning remains a challenging issue. To develop dynamic plasmonic colors, electrochemical, liquid crystal, and electromechanical methods have been proposed; however, there have been limitations in repeatability, flexibility, and scale-up processes. To address these problems, this work proposes a flexible dynamic plasmonic display using dielectric elastomer actuators (DEAs) to isotropically control the interdistance between the metal nanostructures, which can show dynamic coloration without polarization distortion. To replace the expensive and small-scale manufacturing approach, shadow masking and transfer technique with the anodic aluminum oxide (AAO) membrane was applied to realize large-scale and uniformly distributed Au nanodisc array. The differentiated and localized color change in the transmission and reflection modes, such as Janus's face, is realized by proper design of Au nanodisc array on the patterned transparent compliant electrodes formed by silver nanowires and PEDOT:PSS composites. Apparent and locally active color changes appeared in the transmission mode, but almost no color changes were observed in the reflection model by DEA actuation. The proposed system has the potential to activate color filters, cryptographic characters, and next generation display technologies.

Introducing steric groups to thermally activated delayed fluorescence emitter for constructing efficient non-doped solution-processed organic light-emitting diodes

Solution-processed organic light-emitting diodes (OLEDs) remain a reliable approach towards large-area and flexible display devices, but also hold higher requirement on luminescent materials. It is still challenge to develop emitting layers with great solution-processable property and excellent luminous behavior, and especially difficult for non-doped emitting materials. In this work, a TADF emitter, namely 2,3,5,6-tetrakis(4-([1,1':3′,1″-terphenyl]-5′-yl)-9H-carbazol-9-yl)benzonitrile (3Ph-4CzBN), was designed and synthesized by introducing the steric-hindrance triphenyl unit to 2,3,5,6-tetrakis(carbazol-9-yl) benzonitrile (4CzBN) which is usually applied to vacuum evaporation. The incorporation of triphenyl groups significantly increased the molecule weight, thereby rendering 3Ph-4CzBN suitable for solution-processed OLEDs. Meanwhile, 3Ph-4CzBN exhibited two-fold of photoluminescence quantum yield values in pure film than 4CzBN, indicating fluorescence quenching was relatively suppressed by steric groups. The solution-processed OLEDs employed 3Ph-4CzBN as non-doped emitting layer, achieved a maximum external quantum efficiency of 12.8 %, as well as current efficiency and power efficiency up to 34.2 cd A−1 and 23.9 lm W−1, respectively.

Controlled Synthesis of Terbium-Doped Colloidal Gd2O2S Nanoplatelets Enables High-Performance X-ray Scintillators.

Terbium-doped gadolinium oxysulfide (Gd2O2S:Tb3+), commonly referred to as Gadox, is a widely used scintillator material due to its exceptional X-ray attenuation efficiency and high light yield. However, Gadox-based scintillators suffer from low X-ray spatial resolution due to their large particle size, which causes significant light scattering. To address this limitation, we report the synthesis of terbium-doped colloidal Gadox nanoplatelets (NPLs) with near-unity photoluminescence quantum yield (PLQY) and high radioluminescence light yield (LY). In particular, our investigation reveals a strong correlation between PLQY, LY, particle size, and Tb3+concentration. Our synthetic approach allows precise control over the lateral size and thickness of the Gadox NPLs, resulting in a LY of 50,000 photons/MeV. Flexible scintillating screens fabricated with the solution-processable Gadox NPLs exhibited a 20 lp/mm X-ray spatial resolution, surpassing commercial Gadox scintillators. These high-performance and flexible Gadox NPL-based scintillators enable enhanced X-ray imaging capabilities in medicine and security. Our work provides a framework for designing nanomaterial scintillators with superior spatial resolution and efficiency through precise control of dimensions and dopant concentration.

Thermal stability and flexible X-Ray scintillation screen through in-situ assembling Cs3Cu2Cl5 nanocrystals in polymer matrix

Copper-based halides have emerged as promising scintillator materials for X-ray imaging, attributed to their favorable photophysical characteristics, such as negligible self-absorption, high light output, and fast decay. Within this category of materials, Cs3Cu2Cl5 composite polymer scintillator films stand out, delivering excellent performance as flexible X-ray detector screens. However, severe scattering and light degradation induced by the inevitable agglomeration during recombination restricted the application in high-resolution and flexible X-ray imaging. In this study, a Cs3Cu2Cl5@PMMA film prepared by in-situ growth strategy is successfully developed, which represents uniform area, adjustable flexibility and excellent scintillation performance. The prepared large-area film exhibits green emission at 527 nm, with a high light yield, low detection limit and excellent spatial resolution. Meanwhile, the Cs3Cu2Cl5@PMMA film exhibits a remarkable degree of flexibility, enabling imaging applications on non-planar surfaces. Furthermore, it also demonstrates excellent resistance to high temperature environment, maintaining its high-quality imaging performance at 403 K.

Preparation and characterization of transparent advanced smart nanocomposites reinforced by nanofibrillated cellulose/poly(methyl methacrylate)/methyl methacrylate/benzoyl peroxide

Transparent smart nanocomposites, which are among the advanced materials, were developed with the synergistic effect of nanofibrillated cellulose (NFCs) as a natural bionanomaterial, polymethyl methacrylate (PMMA) as a biocompatible microcapsule, methyl methacrylate (MMA) as a monomer, and benzoyl peroxide (BPO) as an initiator and catalyst. Epoxy resin was reinforced with NFC, PMMA, MMA, and BPO. Casting, which appears to be an industrially promising method that allows for cost-effective and high-quantity production, was used for producing transparent advanced nanocomposites. The properties of the nanocomposites, including yield strength, modulus of elasticity, hardness, impact energy, and self-healing capability, were determined. Increases in the yield strength (136.4%), modulus of elasticity (260%), hardness (28.3%), and impact energy (75%) were observed in the transparent smart nanocomposites reinforced with NFC, PMMA, MMA, and BPO, compared to pure epoxy composites. Furthermore, the transparent advanced smart nanocomposites self-healed by about 7% after the notch/scratch defect. It has the potential to be used in a variety of applications, such as interior and structural components for the aerospace and automotive industries, packaging, flexible screens, and lightweight transparent materials.

Responsive Acrylamide-Based Hydrogels: Advances in Interpenetrating Polymer Structures.

Hydrogels, composed of hydrophilic homopolymer or copolymer networks, have structures similar to natural living tissues, making them ideal for applications in drug delivery, tissue engineering, and biosensors. Since Wichterle and Lim first synthesized hydrogels in 1960, extensive research has led to various types with unique features. Responsive hydrogels, which undergo reversible structural changes when exposed to stimuli like temperature, pH, or specific molecules, are particularly promising. Temperature-sensitive hydrogels, which mimic biological processes, are the most studied, with poly(N-isopropylacrylamide) (PNIPAm) being prominent due to its lower critical solution temperature of around 32 °C. Additionally, pH-responsive hydrogels, composed of polyelectrolytes, change their structure in response to pH variations. Despite their potential, conventional hydrogels often lack mechanical strength. The double-network (DN) hydrogel approach, introduced by Gong in 2003, significantly enhanced mechanical properties, leading to innovations like shape-deformable DN hydrogels, organic/inorganic composites, and flexible display devices. These advancements highlight the potential of hydrogels in diverse fields requiring precise and adaptable material performance. In this review, we focus on advancements in the field of responsive acrylamide-based hydrogels with IPN structures, emphasizing the recent research on DN hydrogels.

All-in-one flexible paper-based self-powered energy and display system employing complementary properties of printed PEDOT:PSS/PANI:PSS dual-electrode with a dual-sided triboelectric nanogenerator

A Self-powered energy and display system (SPEDS) has been developed by integrating functionalities of energy harvesting, storage, and multicolor display, heralding innovative solutions for integrated electronic devices. An all-in-one multi-information SPEDS is proposed through incorporating a multicolor electrochromic supercapacitor device (ESCD) with a dual-sided triboelectric nanogenerator (TENG), all screen-printed on a paper substrate. The synergistic enhancement in the conductive, capacitive, and electrochromic performance is realized by exploiting the complementary properties of PEDOT:PSS/PANI:PSS to form a simplified structure of ESCD, in which the electrode and electrochromic layers are integrated into one shared layer, resulting in a wide color gamut and an enhanced capacitive performance of 3.4 mF/cm². Electrochromic electrodes having identical composition exhibit independent color changes at the anode and cathode, thereby featuring a combined color display indicating multi energy-related information. Moreover, the conductive layer fabricated through patterned printing on the paper substrate, serves as both the electrode layer for TENG and the interconnect circuitry with the prepared ESCD. Furthermore, a double-sided TENG was realized by exploiting the triboelectric properties of the paper substrate and then a self-powered energy display wristband was constructed, exemplifying a novelty application utilizing the multi-information indicator properties for energy display derived from the dual-sided friction power generation.

Flexible Anti‐Counterfeiting Circularly Polarized Luminescent Elastomer from Supramolecular Polyurethanes

AbstractSupramolecular polymers with circularly polarized luminescence (CPL) have promoted future intelligence development of polymer‐based materials for flexible display. However, preparing polymer‐based CPL materials with simultaneous enhanced luminescence dissymmetry factor (|glum|) and mechanical performance for industrial applications remains challenging. This work develops an eco‐friendly preparation method for preparing CPL elastomers from supramolecular polyurethanes bearing chiral fluorescent S (or R)‐1,1′‐Bi(2‐naphthol) (BINOL) groups in a solvent‐free system. Surprisingly, a polymer system containing 0.0028 mol% of chiral BINOL unit is sufficient to emit the significant CPL‐activity with a |glum| value of 2.30 × 10−2, appear a good mechanical toughness of 56.28 ± 3.9 MJ·m−3, thereby exhibit multiple flexible anti‐counterfeiting behaviors. The long‐range ordered microphase arrangement in polyurethanes is the key to improving both mechanical properties and |glum|. This is attributed to in‐situ additive polymerization of BINOL‐based isocyanate prepolymer and macromolecular polyols induced helical supramolecular structure, afforded solid‐state films with flexibility and chiral amplification. Furthermore, these results from Circular dichroism, CPL, Fourier transform infrared, X‐ray diffraction analyses, and atomic force microscope confirm the formation of long‐range ordered microphase arrangement through the synergistic effect of hydrogen bonding and π–π interactions. This work offers significant insights into the construction of CPL elastomers for developing novel flexible display materials.

17‐3: Study on Rollable AMOLED Performance Improvement

By considering rollable AMOLED display and application, optical and mechanical performances are discussed and optimized solutions are introduced. Different COE designs for rollable AMOLED are compared in power consumption, L‐decay and reflection. A rollable AMOLED module structure is designed with the impact absorption layer of the hybrid cover. Based on finite element simulation and neutral layer theory, module stack is optimized, accumuled strain is eliminated. Rollable performance and impact resistance are balanced. A portable device with rollable AMOLED is developed. Its mechanical design for rollable display application is introduced.

17‐4: Quantifying Surface Quality due to Periodic Linear Waviness of a Rollable Display

Rollable display has a characteristic feature in assessing surface quality which is caused by a periodic supporter structure. In the presence of such periodic deformation, we suggest a method to quantify them and verified a correlation with human recognition by performing a cognitive experiment. Our method can be utilized in assessing the surface quality including any linear and periodic component.

9‐4: Studies of Physical Properties and Mechanism of Films for Improving Flexibility of Flexible Display

This paper presents the latest technology of displays that have recently been expanding from Rigid to a variety of form factors that can be modified. In a flexible display, different types of films are laminated to ensure panel reliability and to control stress distribution. However, the mechanism for how the characteristics of commercialized films affect the panel has not been properly identified, and it is not easy to adjust the physical properties to find key factors. So we formed a film with various characteristics using UV curing process and found key properties that can affect flexible OLED panel through process change. We were able to confirm the results of the experiment by analyzing and supplementing simulations based on physics. Finally, based on the mechanism proposed by comparing aspects between films, panel characteristics were verified and reliable.