Flexible Optoelectronic Devices Research Articles

Constructing Multi‐Functional Polymeric‐Termination Surface Enables High‐Performance Flexible Perovskite LEDs

AbstractFlexible perovskite light‐emitting diodes (f‐PeLEDs) have attracted increasing interest to realize true‐color, low‐cost, and light‐weight wearable optoelectronic and flexible display applications. However, their external quantum efficiency (EQE) and mechanical stability lag far behind because of the inherent surface and brittle issues of polycrystalline perovskite films. In this work, a multi‐functional polymeric‐termination surface of perovskite film is constructed for achieving efficient and mechanically stable f‐PeLEDs. It takes the roles to not only reduce defects through equipping coordination groups to improve emission properties, but also optimize film morphology and eliminate pinholes to solve the long‐standing issue of leakage current. Meanwhile, the polymeric‐termination surface with anchoring points and polymeric soft chains on perovskites demonstrates synergetic effects beyond the corresponding functional group‐only or polymer‐only strategies in reducing the Young's modulus and improving the mechanical flexibility. Ultimately, the record EQE of 22.1% and significantly enhanced mechanical stability of maintaining 82% of the initial performance after 2000 bending cycles with radius of 5 mm are achieved in pure‐green f‐PeLEDs. The work paves the way for the development of high‐performance flexible optoelectronic devices.

Comprehensive investigation of Thermal Induced Reorganization of Porous-Germanium structures

Porous germanium (PGe) substrates have recently attracted significant attention for the development of lightweight and flexible solar cells and optoelectronic devices. A reliable approach for releasing epitaxial layers based on Germanium and reusing the substrate involves utilizing a bilayer structure of PGe. The growth of such detachable devices holds great potential for integration onto the Si platform. The used structure of PGe is made of a low-porosity layer serving as epitaxial seed on top of high-porosity one used as a weak separation layer. In this work, we investigate the impact of thermal annealing on the PGe morphology for deeper understanding of the mechanisms involved in the formation of the epitaxial seed layer and the voided weak layer underneath. Indeed, thermal-induced reconstruction has been investigated at various annealing temperatures and times for PGe layers with differing porosity levels, encompassing low, high, and gradual porosity profiles. Our findings reveal the formation of a modified substrate at low annealing temperatures, resulting in a suspended membrane on top of the fragile separation layer, rendering it suitable for detachment and subsequent substrate reuse.

Tailoring the optical properties of dye–polymer composite films based on polyvinyl alcohol doped with phenol red toward flexible optoelectronic applications

The composite films of polyvinyl alcohol (PVA) incorporating varying concentrations of phenol red (PR) dye were fabricated using the solution casting method. Structural characteristics of the prepared films were explored through XRD and FTIR spectroscopy analyses. The inclusion of PR dye within the PVA matrix induced cross-linking, enhancing the amorphous nature of the doped PVA samples, as evidenced by XRD patterns. In the presence of PR dopants, the FTIR peaks for PVA exhibited altered intensities and increased width, indicating physical interactions between the functional groups of PVA and PR dopants. The impact of PR additives on the optical properties of PVA was investigated across the spectral range of 190–2500 nm. The PVA/phenol red composite demonstrated enhanced UV blocking in the 190–400 nm wavelength range, rendering it suitable for applications such as UV notch filters, including laser blocking filters. The indirect and direct optical band-gaps of PVA polymer films were reduced from 5.20 eV and 5.78 eV to 4.30 eV and 5.28 eV, respectively, with an increase in the PR filling ratio from 0 wt% to 1.8 wt%. The dispersion region of the refractive index was analyzed using the single oscillator model (Wemple-DiDomenico). Calculation and discussion of values such as dispersion and oscillation energies (Ed and Eo), permittivity at infinite frequency (ε ∞), and lattice contribution to the dielectric function (ε L) of PVA/PR composite films were conducted. These advancements position PVA/PR composite films for potential applications in flexible optoelectronic devices, including light-emitting diodes and photodetectors.

Novel Strategy towards Efficiency Enhancement of Flexible Optoelectronic Devices with Engineered M13 Bacteriophage

Plasmonic nanostructures, which exhibit notable localized surface plasmon resonance (LSPR) properties, are a promising approach for improving the efficiency of fiber‐shaped dye‐sensitized solar cells (FDSSCs) and flexible organic light‐emitting diodes (FOLEDs). Herein, novel plasmonic nanostructure is successfully synthesized via the self‐densification of gold nanoparticles (Au NPs) onto a genetically engineered M13 bacteriophage template. The synthesized Au NP‐M13 bio‐nanostructure show extraordinary gap‐plasmon effects and significantly enhanced LSPR properties compared to randomly dispersed Au NPs for both solid‐state FDSSCs (SS‐FDSSCs) and FOLEDs. Briefly, a power conversion efficiency (PCE) increment of 40.7% is recorded for the Au metallic NPs‐anchored M13 bacteriophage (Au NPs‐M13) enhanced SS‐FDSSCs; whereas an external quantum efficiency (EQE) increment of 47.2% is achieved for the Au NPs‐M13 enhanced FOLEDs.

Strain modulated optical properties of MoSi2P4 monolayer – insights from DFT

Strain plays a very important role in tuning the properties of the materials for the desired applications. In the present work, we have investigated the variation of strain on the electronic and optical properties of a recently synthesized class of compound MoSi2P4 monolayer using the first principle methods. The MoSi2P4 monolayer is found to be dynamically and thermally stable at room temperature. The electronic structure of studied monolayer indicates a direct bandgap (at K-point) of 0.685 eV and 1.177 eV using the PBE and HSE06 hybrid functionals, respectively. To tune the electronic bandgap and optical properties, mechanical strain was applied (up to ±10%). A high optical absorption coefficient of the order of 105 cm−1 is observed. The absorption starts in the infrared and visible region covering a large part in the ultraviolet region. The absorption coefficient is found to decrease (increase) under tensile (compressive) strain. Our study indicates the potential application of MoSi2P4 monolayer in flexible optoelectronic devices for absorption and detection in the infrared, visible and ultraviolet region.

Visible-light photoelectric performance and bending stability of flexible LaCoO3/Mica thin films

New energy sources such as solar energy have been developed and utilized due to the shortage of non-renewable energy, and photoelectric materials have attracted more attention, accordingly. Moreover, flexible optoelectronic devices are crucial in the fields of wearable artificial intelligence, portable energy, and smart medical care. At present, photoelectric devices based on traditional perovskite cobalt oxide rigid films have problems such as inability to bend and deformation, which limits their application environment. Here, natural mica with atomically flat surface, high thermal stability, high transparency and good mechanical flexibility was selected as the substrate for preparing a series of LaCoO3 flexible photoelectric films. These films exhibit excellent photoelectric properties and flexible properties. More importantly, the flexible film still has fast response speed and reproducible light response after 500 bending cycles. It reveals that all-inorganic perovskite LaCoO3 is a promising candidate for designing high-performance, flexible and wearable optoelectronic devices.

Advances and Challenges in Bio-Inspired Cameras Based on Flexible and Stretchable Optoelectronic Devices

Advances and Challenges in Bio-Inspired Cameras Based on Flexible and Stretchable Optoelectronic Devices

Controlled exfoliation of wafer-scale single-crystalline AlN film on MOCVD-grown layered h-BN

In this work, we present a stress-free AlN film with improved crystal quality assisted by h-BN and demonstrate the mechanical exfoliation of wafer-scale single-crystal AlN freestanding membrane and reveal the controllable exfoliation mechanism of AlN. Uniform and continuous wafer-scale h-BN is directly grown on c-plane sapphire using a flow modulation epitaxy mode by metal-organic chemical vapor deposition. The nucleation and evolution processes of quasi-van der Waals epitaxy (QvdWE) of AlN on h-BN are revealed. It is found that O2-plasma-treated h-BN can effectively promote the nucleation islands of AlN and contribute to the release of biaxial stress and the reduction of dislocation density in the epilayers. Eventually, the QvdWE growth of a stress-free AlN film (0.08 GPa) is achieved, and wafer-scale mechanical exfoliation of the AlN membrane has been realized. This work provides an effective strategy for the quality improvement of III-nitride films and paves the way for the vertical structure and flexible deep-ultraviolet optoelectronic devices.

Semiconductor Membrane Exfoliation: Technology and Application

AbstractFlexible semiconductor film‐based optoelectronic devices have garnered significant attention in emerging fields such as the Internet of Things (IoT), wearable devices, and smart healthcare due to their wide range of applications. It is challenging to directly grow the foundational materials of optoelectronic devices, specifically semiconductor thin film structures, on flexible substrates. Instead, they are typically fabricated on conventional rigid thick semiconductor substrates. Consequently, the exfoliation and transfer of epitaxial semiconductor thin film structures onto substrates constitute pivotal steps in the production of flexible optoelectronic devices. The integration of hard inorganic semiconductor materials with flexible substrates offers a solution to the limitations of rigidity and brittleness associated with conventional optoelectronic devices and can be used to address challenges from design to manufacturing. This review provides a comprehensive overview of the working principles and recent advances of various techniques aimed at achieving the membrane exfoliation and transfer of semiconductor structures on conventional rigid substrates. It also reviews the possible applications of the transferred membrane in a variety of optoelectronic devices. Finally, it offers insights into the potential of high‐end semiconductor manufacturing and flexible semiconductor devices to play a critical role in advancing next‐generation optoelectronics technologies.

High-performance composite transparent electrode composed of ultra-long silver nanowires and antimony-doped tin oxide nanoparticles

Composite transparent conductive electrodes (TCEs) consisting of silver nanowires (AgNWs) and conductive metal oxides are very promising for flexible optoelectronic devices due to their smooth surface morphology and high chemical stability. However, it is still challenging to ensure high optoelectronic performance and long-term stability in practical applications. Here, we solved these problems by coating antimony-doped tin oxide (ATO) nanoparticles dispersion on ultra-long AgNWs network using waterborne polyurethane (WPU) binder. Ultra-long nanowires occupy less wire-wire junctions and space than short nanowires, thus increasing the optoelectronic performance and flexibility of the composite TCE. WPU improves the adhesion and stability of ATO nanoparticles to the substrate and AgNWs network. The fabricated composite TCE showed a low sheet resistance of 11.9 Ω sq−1, good optical transmittance of 83% at 550 nm and a figure of merit (FOM) of 162 compared to PET/ITO electrode. It also showed excellent mechanical flexibility, adhesion to the substrate and solvent stability. Furthermore, the long-term conductivity was maintained under ambient conditions for 60 days.

Synthesis of ZnO nanorods decorating with Ag nanoparticles on flexible polyimide substrate for visible photodetector application

Polyimide (PI), which have many remarkable features such as excellent mechanical strength, outstanding thermal stability, exceptional electric properties, etc, is a potential carrier for optoelectronic devices due to its abundant applications. However, because of chemical inertness and smooth surface that led to the growth of materials on this substrate being more complex than that on rigid substrate, thus, this report aims to emphasise the synthesis of ZnO NRs decorated with the Ag NPs on flexible substrate for photodetector application. In this study, we successfully synthesise ZnO NRs/Ag NPs on a flexible PI substrate by the hydrothermal method. The performance of our photodetector in visible region (395 nm) exhibits via the responsivity of the device, which recorded value of ca. 40.16 mA W−1 at 1.66 mW cm−2. With obtained results, our research can pave the way for future studies based on flexible optoelectronic devices.

Aggregation induced strong photoluminescence at room temperature in large-area C8BTBT thin films

Study of optical properties of 2,7-dioctyl[1]benzothieno[2,3-b]benzothiophene (C8BTBT) is promising for applications in low-cost and flexible optoelectronic devices. Here, we systematically investigated the thickness dependent structural and photophysical properties of large-area C8BTBT films. The large-area C8BTBT thin films of different thickness below 80 nm were prepared by off-centre spin coating method. Grazing incidence X-ray diffraction measurements confirm the highly crystalline nature of the thin films and reveal that crystal coherence length increases with increase of film thickness. The film morphology and its thickness were studied using atomic force microscopy. Further, optical absorption and emission behaviors of the thin films were analyzed. The results show strong ultraviolet (UV) emissions at room temperature. The photoluminescence behaviour of higher-thickness films differs from that of lower-thickness films. The thickness dependent UV emission spectra are explained in terms of defects and aggregation behavior of C8BTBT thin films. We determine the impact of thickness and aggregation (J- and H-type) on emission behaviors of the C8BTBT thin films. Our findings open a new avenue for the future optimization and prospective applications in photonics based on two-dimensional organic semiconductors.

Thermal Radiation Annealing for Overcoming Processing Temperature Limitation of Flexible Perovskite Solar Cells.

Common polymeric conductive electrodes, such as polyethylene terephthalate (PET) coated with indium tin oxide, face a major challenge of their low processing-temperature limits, attributed to PET's low glass transition temperature (Tg of 70-80°C). This limitation significantly narrows the scope of material selection, limits the processing techniques applicable to the low Tg, and hinders the ripened technology transfer from glass substrates to them. Addressing the temperature constraints of the flexible substrates is impactful yet underexplored, with broader implications for fields beyond photovoltaics. Here we introduce a new thermal radiation annealing methodology to address this issue. By applying above Tg radiation annealing in conjunction with thermoelectric cooling, we successfully create highly ordered molecular packing on PET substrates, which are exclusively unachievable due to PET's low thermal tolerance. As a result, in the context of perovskite solar cells, this approach enables the circumvention of high-temperature annealing limitations of PET substrates, leading to a remarkable flexible device efficiency of 22.61% and a record fill factor of 83.42%. This approach proves especially advantageous for advancing the field of flexible optoelectronic devices. This article is protected by copyright. All rights reserved.

Electrical, optical and mechanical properties of monolayer MoTe2 for applications in wearable optoelectronic devices

Transition metal dichalcogenides (TMDs) have excellent optical and mechanical properties and have potential application value in wearable optoelectronic response devices. MoTe2, a representative material of TMDs, is studied by first-principles calculation in this paper. The results show that the MoTe2 monolayer has a direct band gap of 1.110eV, which has a strong light absorption capacity and can produce a high concentration of photogenerated charge carriers after light absorption. The material is soft and exhibits the unique mechanical properties of layered materials. The effects of biaxial strain and defects on the properties of the materials were analyzed. The results show that the biaxial compression strain can enhance the light absorption curve of the material, enhance the light absorption of the photogenerated carrier, and expand the range of its energy distribution. The tensile strain decreases the value of the photon absorption curve and decreases the range of energy distribution of photogenerated carriers. The Mo vacancy defect increases the absorption curve value in the low energy region and broadens the optical response range of the material. The two types of vacancy defects both induce a ‘discrete’ distribution of photogenerated carriers. The Mo vacancy significantly affects the elastic modulus and anisotropy properties of the material, resulting in the material changing from ductile to brittle. When Mo vacancy is added, the spatial distribution of the elastic modulus of the material also changes greatly. Therefore, MoTe2 has potential application in flexible optoelectronic devices, and its performance can be controlled by strains and defects.

A hybrid density functional study of tensile-induced changes in phonon dispersion, electronic structure and optical absorption of bilayer BN for optoelectronic applications

The electronic, phonon dispersion and optical properties of bilayer BN have been investigated with density functional theory (DFT) calculations. Interestingly, applying the biaxial strain of 4% converts the indirect band gap of bilayer BN to a direct band gap. We show that the interaction between the BN layers results in the removal of two-fold degeneracy and separation of ZA and ZO phonon modes near the Γ point. Across the entire range of applied biaxial tensile strains, the bilayer BN exhibits a dynamically stable behavior. The phonon bandgap of bilayer BN decreases under tensile strain. The bilayer BN has strong adsorption in the UV region and the optical absorption peaks are red-shifted by applying the tensile strain. These findings are essential for the strain engineering of bilayer BN and future fabrication of flexible electronic and optoelectronic devices.

Paper-based flexible photodetector functionalized by WS2/Ti3C2Tx 2D-2D heterostructures

Paper-based photodetectors are gaining attention in the field of optoelectronics due to their low cost, flexibility, and eco-friendliness. The paper-based devices have applications in areas like wearable devices, environmental monitoring, and point-of-care diagnostics, where these photodetectors exhibit significant potential. In the present work, we fabricated paper-based photodetectors functionalized by WS2/Ti3C2Tx heterostructures. These materials were characterized by X-ray diffractometer, UV–visible spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, Energy dispersive spectroscopy, and Scanning electron microscopy. We fabricated a paper-based flexible device from this WS2/Ti3C2Tx composite using a solvent-free, easily available, and cost-effective Hand-print method. We studied the I–V & I-t response of this device. The as-synthesized device shows excellent photodetection properties with a responsivity value of 3.06 mA/W, and 5.93 × 108 Jones specific detectivity. We further investigated the flexibility and durability of these devices. Finally, the current study supports a substantial advancement in the design of reliable, flexible, and large-area optoelectronic devices.

Completely annealing-free flexible Perovskite quantum dot solar cells employing UV-sintered Ga-doped SnO2 electron transport layers

The electron transport layer (ETL) is a critical component in perovskite quantum dot (PQD) solar cells, significantly impacting their photovoltaic performance and stability. Low-temperature ETL deposition methods are especially desirable for fabricating flexible solar cells on polymer substrates. Herein, we propose a room-temperature-processed tin oxide (SnO2) ETL preparation method for flexible PQD solar cells. The process involves synthesizing highly crystalline SnO2 nanocrystals stabilized with organic ligands, spin-coating their dispersion, followed by UV irradiation. The energy level of SnO2 is controlled by doping gallium ions to reduce the energy level mismatch with the PQD. The proposed ETL-based CsPbI3-PQD solar cell achieves a power conversion efficiency (PCE) of 12.70%, the highest PCE among reported flexible quantum dot solar cells, maintaining 94% of the initial PCE after 500 bending tests. Consequently, we demonstrate that a systemically designed ETL enhances the photovoltaic performance and mechanical stability of flexible optoelectronic devices.

Power-efficient and high-performance potential of pentacene transistors enabled by metal-nitride gate insulators fabricated with nitrogen plasma

The demand for next-generation organic field-effect transistors (OFETs) with low operating voltage is becoming gradually attractive in many application areas, such as flexible/wearable medical sensors and stretchable electronics. While using high dielectric materials is a potent approach, it often results in a decline in field-effect mobility or on/off ratio. Unfortunately, achieving low-voltage operation has hindered practical applications, compromising device performance. Here, we discovered for the first time a novel class of low-driving voltage pentacene transistors adopting gate insulators composed of nitrogen-plasma-reacted AlNx, TiNx, and TaNx. This exciting discovery is simple, affordable, environmentally friendly, and secure. X-ray photoelectron spectrometer (XPS) analysis reveals that the as-formed metal nitrides are composited with certain native oxide components, exhibiting outstanding leakage current blocking capacity and a high dielectric constant. Further, the surface energy of metal nitrides was altered by applying a thin layer of poly-(4-vinylphenol) (PVP). This modification improved the growth of pentacene grains and the insulator/pentacene interface. The best devices by comprehensive evaluation, the TiNx samples, achieve a high average of field-effect mobility ∼1.41 cm2/Vs, a subthreshold swing of 0.19 V/dec, an on/off current ratio of ∼104, and a turn-on voltage close to 0 V, which shows promising potential candidates for the flexible electronic devices, optoelectronic devices, and neuromorphic application.

Pushing the thinness limit of silver films for flexible optoelectronic devices via ion-beam thinning-back process

Reducing the silver film to 10 nm theoretically allows higher transparency but in practice leads to degraded transparency and electrical conductivity because the ultrathin film tends to be discontinuous. Herein, we developed a thinning-back process to address this dilemma, in which silver film is first deposited to a larger thickness with high continuity and then thinned back to a reduced thickness with an ultrasmooth surface, both implemented by a flood ion beam. Contributed by the shallow implantation of silver atoms into the substrate during deposition, the thinness of silver films down to 4.5 nm can be obtained, thinner than ever before. The atomic-level surface smooth permits excellent visible transparency, electrical conductivity, and the lowest haze among all existing transparent conductors. Moreover, the ultrathin silver film exhibits the unique robustness of mechanical flexibility. Therefore, the ion-beam thinning-back process presents a promising solution towards the excellent transparent conductor for flexible optoelectronic devices.

Biopolymer blend composite films based on polyvinyl alcohol/ chitosan/ grape seed extract via green approach for flexible optoelectronic devices

The flourishing environmental concerns have grabbed the attention of researchers developing environmentally supportive materials in various fields. A green approach was used to create biopolymer blend composites based on polyvinyl alcohol (PVA) and chitosan (CS) doped with various concentrations of grape seed (GS). Various analytical techniques, such as Fourier-transform infrared spectroscopy (FTIR), UV–visible (UV) spectra, field emission scanning electron microscope (FE-SEM) and differential scanning calorimetry (DSC) were used to evaluate the optical, structural and thermal properties of the prepared blend composites. The optical properties of blend composites were determined by UV spectroscopy and the findings revealed that absorption intensity increased with increasing GS, while bandgap energy decreased from 4.18 eV for pure blend to 2.91 eV for blend/15 wt% GS. The homogeneous distribution of GS particles in the biopolymer blend was identified with FE-SEM images. DSC results showed that increasing the GS content increased the glass transition temperature of the blend composites. The AC conductivity and dielectric constant were measured using the LCR meter. The conductivity rises with increasing frequency and dosage of GS, with the greatest conductivity obtained at 15 wt% loading. In comparison to a pure blend, it was discovered that the inclusion of 15 wt% GS enhanced the tensile strength by 50%, hardness by 17% and the reduction in elongation at break by 19 %. As a consequence, environmentally friendly PVA/CS/GS biopolymer blend composites with excellent mechanical, thermal, electrical, and dielectric parameters might be a viable green option for flexible electronic, electrochemical and energy storage devices.