Photoactive Devices Research Articles

A predictive screening tool to evaluate the efficiency of Z/E photoisomerizable molecular switches

The evaluation of the Z/E photoisomerization efficiency is an essential task to design photoactive molecular devices. Nevertheless, this photoreactivity can be correctly described only by applying extensive and expensive computational methods. In this study, a predictive tool to screen the photoinduced Z/E isomerization efficiency of molecular switches is presented, based on three key properties: the structure of the ground state minimum, the nature of the electronic transition populating the optically bright state, and the presence of crossings between the optically bright state and the one lower in energy. Our methodology allows evaluating these properties by few and affordable calculations, potentially enabling the screening of large sets of photoswitches. After presenting the formal aspects, the tool is applied to model systems of paradigmatic classes of photoswitches (retinal, green fluorescent protein, hemithioindigo, chiroptical, and stilbene compounds) including derivatives. A comparison with the available experimental data is performed to validate our approach.

Unusual bendable soft molecule‐based ferroelectric crystals enabling the flexible photo‐pyroelectric detection

AbstractSoft molecule‐based ferroelectrics with unique structural flexibility hold a promise for versatile applications of non‐volatile memory, imaging and photovoltaic devices. Except for few polymers (e.g., polyvinylidene fluoride, PVDF), it is challenging to exploit soft ferroelectric crystals toward free‐standing flexible photoactive devices. We here report a multiaxial soft molecule‐based ferroelectric, (n‐PA)2PbCl4 (1, where n‐PA+ is n‐pentylammonium), of which spontaneous polarization can be reversibly switched in both crystal and powder forms. Strikingly, single crystals of 1 have unusual structural flexibility and bendability, achieving the self‐standing bending with a bending radius of ~0.22 mm. Besides, the pyroelectric activities are also preserved for these single crystals after several bending cycles. Further, the bendable crystal‐based photodetector of 1 allows broadband photoactivities via the photo‐pyroelectric effect, covering a wide range from 405 to 940 nm spectral region, breaking through the limit of optical absorption bandgap. As the first study of bendable free‐standing photo‐pyroelectric detectors in ferroelectric crystals, our work sheds light on the assembly of flexible smart photoelectric devices.image

A Review of Phototoxic Plants, Their Phototoxic Metabolites, and Possible Developments as Photosensitizers.

This study provides a comprehensive overview of the current knowledge regarding phototoxic terrestrial plants and their phototoxic and photosensitizing metabolites. Within the 435,000 land plant species, only around 250 vascular plants have been documented as phototoxic or implicated in phototoxic occurrences in humans and animals. This work compiles a comprehensive catalog of these phototoxic plant species, organized alphabetically based on their taxonomic family. The dataset encompasses meticulous details including taxonomy, geographical distribution, vernacular names, and information on the nature and structure of their phototoxic and photosensitizing molecule(s). Subsequently, this study undertook an in-depth investigation into phototoxic molecules, resulting in the compilation of a comprehensive and up-to-date list of phytochemicals exhibiting phototoxic or photosensitizing activity synthesized by terrestrial plants. For each identified molecule, an extensive review was conducted, encompassing discussions on its phototoxic activity, chemical family, occurrence in plant families or species, distribution within different plant tissues and organs, as well as the biogeographical locations of the producer species worldwide. The analysis also includes a thorough discussion on the potential use of these molecules for the development of new photosensitizers that could be used in topical or injectable formulations for antimicrobial and anticancer phototherapy as well as manufacturing of photoactive devices.

Coherent Phonon Manipulation via Electron-Phonon Interaction for Facilitated Relaxation of Metastable Centers in ZnO.

Methods that allow versatile manipulation of metastable centers in semiconductors are highly important owing to their potential for quantum information processing and computations. In this study, we demonstrate that the electron-phonon interaction enables phonon participation to promote relaxation of metastable centers in ZnO, which is known for its persistent photoconductivity (PPC) effect. Experimentally, we show that continuous infrared (IR) radiation (1064 nm, ∼30 mW/cm2) promotes longitudinal optical phonons via the Fröhlich interaction and increases the PPC relaxation rate by ∼4 folds. More importantly, we discover that coherent phonons activated by an ultrashort pulse IR laser of the same power increased the relaxation rate by ∼1200-fold, as confirmed by ultrafast transient spectroscopy to be correlated to the excitation of coherent acoustic phonons via the inverse piezoelectric effect. We expect this study to provide valuable guidance for the development of novel quantum and photoactive devices.

Photoactive materials and devices for energy-efficient soft wearable optoelectronic systems

Advances in conventional inorganic photoactive materials, such as silicon and III–V compound semiconductors, enabled the development of high-performance and energy-efficient optoelectronic devices (e.g., photodetectors (PDs), light-emitting devices (LEDs), and photovoltaics (PVs)). These devices have recently been considered as essential components for multifunctional wearables that are capable of either providing a long-term stable power supply or visualizing various healthcare indicators in real time. Despite such progress, their rigid and bulky properties pose undesired challenges associated with low signal-to-noise ratios (SNRs) originating from a mechanical modulus mismatch between the skin and device, uncontrolled strain-induced crack propagation, and even long-term discomfort. As alternatives, emerging photoactive materials, such as atomically thin two-dimensional (2D) nanosheets and organic–inorganic halide perovskites with ultra-lightweight, ultrathin, and flexible characteristics have been significantly explored. These materials showed low-power multispectral sensing, effective light-matter coupling, and high compatibility to existing micro-/nano-fabrication technologies even on curved surfaces. Considering stretchability beyond flexibility, numerous research groups have employed well-established mechanical designs including a pre-strain-induced buckled structure with ultrathin layers, neutral-mechanical plane, and rigid-island array configuration with wavy interconnects. Recently, in addition to the above methodology, novel materials strategies regarding intrinsic stretchability and autonomous self-healability were introduced to improve the areal density and electrical/mechanical reliability through removal of serpentine interconnects, as well as adoption of tough damage-resistant polymers with efficient strain dissipation, low glass-transition temperature, and dynamically crosslinked bonds. In this light, the aforementioned methods would be essential to make current flexible photoactive devices intrinsically and durably stretchable. Here, we provide an overview of high-performance photovoltaic/photoemissive materials and devices and their applications to soft wearable energy-efficient optoelectronic systems. In particular, materials synthesis, device fabrication/assembly, and reconfigurable integration used in photoactive material-based wearable modular optoelectronic systems were timely described through a rigorous review of recent results.

Preparation of Ultrathin and Degradable Polymeric Films by Electropolymerization of 3-Amino-l-tyrosine.

Bioderived polymers are one of many current research areas that promise a sustainable future. Due to their unique properties, the bioderived polymer polydopamine has been in the spotlight over the last decades. Its ability to adhere to virtually any surface and its stability over a wide pH range as well as in several organic solvents make it a suitable candidate for various applications like coatings and biosensors. However, strong light absorption over a broad range of wavelengths and high quenching efficiency limit its uses. Therefore, new bioderived polymers with similar features to polydopamine but without fluorescence quenching properties are highly desirable. Herein, the electropolymerization of a bioderived analog of dopamine, 3-amino-l-tyrosine, is demonstrated. The resulting polymer, poly(amino-l-tyrosine), exhibits several characteristics complementary to or even exceeding those of polydopamine and its analog, polynorepinephrine, rendering poly(amino-l-tyrosine) attractive for the development of sensors and photoactive devices. Cyclic voltammetry, spectro-electrochemistry, and electrochemical quartz crystal microbalance measurements are applied to study the electrodeposition of this material, and the resulting films are compared to polydopamine and polynorepinephrine. Impedance spectroscopy reveals increased ion permeability of poly(amino-l-tyrosine) compared to polydopamine and polynorepinephrine. Moreover, the reduced fluorescence quenching of poly(amino-l-tyrosine) supports its use as coating for biosensors and organic semiconductors.

Erratum to: Development of Photoactive Supramolecular Devices and Machines

Erratum to: Development of Photoactive Supramolecular Devices and Machines

The photosensitive activity of organic/inorganic hybrid devices based on Aniline Blue dye: Au nanoparticles (AB@Au NPs)

In this study, Aniline Blue (AB) synthetic triarylmethane dye and AB:Au NPs mixture films were deposited on n-Si by spin coating technique to form an organic/inorganic hybrid electro-optic device. Thus, Co/AB/n-Si (named D1) and Co/AB:Au NPs (1%)/n-Si (named D2) photoactive devices were fabricated, and current-voltage (I–V) measurements were performed on both devices to investigate electrical properties under dark and various light illumination intensities changes from 100 to 400 mW/cm2. Sensitivity and responsivity as well as specific detectivity of both devices were obtained depending on the reverse bias voltage for various light intensities. The main device parameters such as ideality factor (n), barrier height (Фb), series resistance (Rs) and experimental interface states density (Nss) were calculated and discussed in details. The light intensity-dependent I–V measurements revealed that the reverse bias current increased with the increasing of the light intensity and confirmed photodiode behaviors. The illumination coefficient (m) values were also extracted from the light-intensity dependent I–V characteristics and obtained as 0.87 and 1.28 for D1 and D2, respectively. Furthermore, the D2 device exhibited a higher response to the light than D1 due to the surface plasmon resonance effect of Au NPs. The capacitance-voltage (C–V) and conductance-voltage (G-V) characteristics of both devices were also studied in details under dark at 500 kHz applied frequency. As a result, the experimental results highlight that the D1 and D2 devices can be used in various optical applications such as photodiodes, photodetector and carrier storage devices.

Coupled Electromagnetic and Hydrodynamic Modeling for Semiconductors Using DGTD

A hydrodynamic model (HDM) solver based on discontinuous Galerkin time domain finite element method (DGTD-FEM) has been developed in order to simulate the transient charge transport in semiconductors. The bipolar transport equations have been numerically solved together with the Poisson equation to realize ballistic charge transport in semiconductor devices. Furthermore, the developed solver is coupled with an FEM-based full-wave Maxwell solver in order to model the behavior of semiconductors under external electromagnetic illumination. This multiphysics coupled solver is capable of simulating transient behavior of photoactive semiconductor devices that are illuminated by externally modulated light at high frequencies. With the time domain HDM solver, the inertia effects and ballistic transport are also accounted in the accurate transient simulations of high-frequency photoactive devices.

Energy conversion dynamics of novel lanthanide-doped forsterite photoactive devices

Forsterite (Mg2SiO4) is an easily dopable dielectric oxide with elevated transparency in the ultraviolet (UV), visible (Vis), and near-infrared (NIR) ranges. Despite its properties, the use of forsterite as a phosphor host has not been extensively studied. In this paper, Mg2SiO4 was used as a host for different combinations of Er3+, Eu3+, and Yb3+. The insertion of multiple dopants in the forsterite structure is presented for the first time. DC and UC photoluminescence were measured with excitation at 380, 976, and 1470 nm. Yb3+-doped forsterite showed an elevated UC emission at 480 nm (blue) due to the cooperative luminescence (CL) allowed by the host. Interestingly, the efficiency of the Er3+ UC and DC emissions involving the 4I11/2 level considerably increased in the presence of Eu3+. The Eu3+ ion serves as energy storage for Er3+ in the Mg2SiO4 crystal, presenting a behavior never reported in other hosts. Er3+/Eu3+/Yb3+ co-doped nanoparticles showed the highest DC emission among the samples under 976 nm excitation, indicating the insertion of Eu3+ as an alternative to improve Er3+/Yb3+-doped waveguide amplifiers. Moreover, the Er3+/Eu3+/Yb3+ co-doping resulted in efficient energy conversion from the NIR and UV to the Vis, the main spectral range for solar cell applications.

Comprehensive Non-volatile Photo-programming Transistor Memory via a Dual-Functional Perovskite-Based Floating Gate.

Photonic transistor memory has received increasing attention as next-generation optoelectronic devices for light fidelity (Li-Fi) application due to the attractive advantages of ultra-speed, high security, and low power consumption. However, most transistor-type photonic memories developed to date still rely on electrical bias for operation, imposing certain limits on data transmission efficiency and energy consumption. In this study, the dual manipulation of "photo-writing" and "photo-erasing" of a novel photonic transistor memory is successfully realized by cleverly utilizing the complementary light absorption between the photoactive material, n-type BPE-PTCDI, in the active channel and the hybrid floating gate, CH3NH3PbBr3/poly(2-vinylpyridine). The fabricated device not only can be operated under the full spectrum but also shows stable switching cycles of photo-writing (PW)-reading (R)-photo-erasing (PE)-reading (R) (PW-R-PE-R) with a high memory ratio of ∼104, and the memory characteristics possess a stable long-term retention of >104 s. Notably, photo-erasing only requires 1 s light illumination. Due to the fully optical functionality, the rigid gate electrode is removed and a novel two-terminal flexible photonic memory is fabricated. The device not only exhibits stable electrical performance after 1000 bending cycles but also manifests a multilevel functional behavior, demonstrating a promising potential for the future development of photoactive electronic devices.

Development of Photoactive Supramolecular Devices and Machines

Among the various directions of the science of photoactive organic compounds, the design, creation, and study of photoactive supramolecular devices and machines are attracting special attention, since in this way it is possible to discover new approaches to construct complex hierarchical “smart” materials.

Pixelated full-colour small molecule semiconductor devices towards artificial retinas

Variable bandgap conjugated donor–acceptor small molecule thin films show absorption spectra similar to those of human eye's photoreceptors. Photoactive devices interfaced with a bio-electrolyte reveal capacitive photocurrent response making them suitable for future full-colour retinal prosthesis.

Enhanced Synchronously Emission Dissymmetry Factor and Quantum Efficiency of Circularly Polarized Phosphorescence from Point-Chiral Cyclometalated Platinum(II) Liquid Crystal

Circularly polarized luminescence (CPL) derived from supramolecular self-assembly chirality has been a fascinating field of research due to its applications in photoactive devices and bioactive pro...

Pulsed Force Kelvin Probe Force Microscopy.

Measurement of the contact potential difference (CPD) and work functions of materials are important in analyzing their electronic structures and surface residual charges. Kelvin probe force microscopy (KPFM), an imaging technique of atomic force microscopy, has been widely used for surface potential and work function mapping at the nanoscale. However, the conventional KPFM variants are often limited in their spatial resolution to 30-100 nm under ambient conditions. The continuingly decreasing size and increasing complexity of photoactive materials and semiconductor devices will present future challenges in uncovering their nanometer-scale electrical properties through KPFM. Here, we introduce a KPFM technique based on the pulsed force mode of atomic force microscopy. Our technique, named pulsed force Kelvin Probe Force Microscopy (PF-KPFM), is a single-pass technique that utilizes the intrinsic Fermi level alignment between the AFM tip and the conductive sample without the need for an external oscillating voltage. Induced cantilever oscillations generated by a spontaneous redistribution of electrons between tip and sample are extracted and used to obtain the cantilever oscillation amplitude and to derive the surface potential. The spatial resolution of PF-KPFM is shown to be <10 nm under ambient conditions. The high spatial resolution surface potential mapping enables in situ determination of ohmic and nonohmic contacts between metals and semiconductors, mapping boundaries of ferroelectric domains of BaTiO3, as well as characterization of protein aggregates. High spatial resolution measurements with PF-KPFM will facilitate further studies directed at uncovering electrical properties for emerging photoactive materials, biological samples, and semiconductor devices.

17.1% Efficient Single-Junction Organic Solar Cells Enabled by n-Type Doping of the Bulk-Heterojunction.

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC71BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

Electrostatic Control of Photoisomerization Pathways in Proteins

Rotation around a specific bond after photoexcitation is central to vision and emerging opportunities in optogenetics, super-resolution microscopy, and photoactive molecular devices. Competing roles for steric and electrostatic effects that govern bond-specific photoisomerization have been widely discussed, the latter originating from chromophore charge transfer upon excitation. We systematically altered the electrostatic properties of the green fluorescent protein chromophore in a photoswitchable variant, Dronpa2, using amber suppression to introduce electron-donating and electron-withdrawing groups to the phenolate ring. Through analysis of the absorption (color), fluorescence quantum yield, and energy barriers to ground- and excited-state isomerization, we evaluate the contributions of sterics and electrostatics quantitatively and demonstrate how electrostatic effects bias the pathway of chromophore photoisomerization, leading to a generalized framework to guide protein design.

Weak Intramolecular Interactions to Stabilize Supramolecular Fullerene‐Porphyrin Conjugates and to Control the Conformation of Multiporphyrinic Arrays

AbstractInvited for the cover of this issue is Jean‐François Nierengarten from the University of Strasbourg and CNRS, France. The cover image shows an artistic view of a research team discussing weak intramolecular interactions involving metalloporphyrins. Minutes of this group meeting are presented in a minireview highlighting how such interactions have been used to stabilize photoactive supramolecular devices and to control the conformation of large multiporphyrinic arrays.

Ultrafast terahertz transmission/group delay switching in photoactive WSe2-functionalized metaphotonic devices

The emergence of larger-scaled two-dimensional (2D) layered materials has attracted intense research efforts and significant progress in the area of photonics and optoelectronics recently. As a remarkable representative of 2D materials, transition metal dichalcogenides (TMDCs) have demonstrated an astonishing photoconductivity and the ultrafast charge carrier dynamics, which provides excellent potentials for ultrafast optical modulators. Herein, by simply transferring a high-quality CVD-grown WSe2 multilayer on plasmon-induced transparency (PIT) metasurfaces, we demonstrate that the transmission amplitude modulation is as high as 43% and the slow light switching is up to 6 ps in the THz regime. Under photoexcitation, both functionalities are dynamically controlled within ~8 ps owing to a merit of ultrafast free carriers’ relaxation in the WSe2 multilayer. Moreover, a theoretical model consisting of two coupled harmonic oscillators and the near-field distributions are simultaneously employed to verify the strong dependence of the active PIT switching behavior on the suppression of the bright mode of split ring resonators. Our proposed versatile active WSe2-functionalized metasurface with a low cost and simple manufacturing will give researchers new insights into the ultrafast switchable metaphotonic devices.

Ultra-broadband photoresponse of localized surface plasmon resonance from Si-based pyramid structures

Structures capable of exciting localized surface plasmon resonance (LSPR) have been widely utilized to increase photoresponse in many photoactive devices. However, most LSPR can be induced in only a small spectral range and with particular polarization. Here, LSPR with ultra-broadband response is revealed. Light detection using such LSPR is also explored to exhibit a spectral range covering the visible to mid-infrared. The strong LSPR induced by the inverted pyramid array structure enables a Si-based Schottky photodetector to detect photons even with energy lower than the Schottky barrier height, leading to the experimental measurement covering from 300 to 2700 nm. Theoretical evaluation even predicts a response beyond 4000 nm.