This PDF file contains the front matter associated with SPIE Proceedings Volume 10529, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We report the formation of hybrid states of self-assembled PTCDI-C7 organic molecule excitons and surface plasmon polaritons (SPP). Ten self-assembled monolayers with no host matrix are directly evaporated onto a gold thin film forming a ultra-dense and organized, 30nm thick layer. The π- π stacking among molecules leads to the formation of H-aggregates with alignment of molecular dipole moments along the local electric field vector. This collective excitations are known to give rise to a sharp excitonic peak in absorption with large oscillator strength, which are favorable properties for the observation of strong coupling. Experimental wavevector-resolved reflectance spectra display an anticrossing, attesting the strong coupling regime with a Rabi splitting energy ΩR=102 meV at room temperature. By contrast, no anticrossing has been observed for PTCDI-C7 molecules evaporated in a different experimental condition and with a reduced local order. We interpret the observed strong coupling regime as resulting from the high degree of organization and the controlled molecular dipole orientation. Under optical pumping, we observe an enhancement of the coupling efficiency between the molecular emission and the SPP mode. This observation is consistent with the small oscillator strength of the lowest Frenkel state of exciton and to the large Stokes shift of PTCDI-C7 molecules induced by H-aggregate stacking. The use of ultra-dense layers of self-assembled molecules opens interesting perspectives for the control of the molecular dipole orientation at the nanoscale to maximize interaction with the SPP field and therefore the strong coupling strength.

Organic light-emitting diode (OLED) materials were deposited directly on a concave glass surface using the electrospray deposition (ESD) technique to obtain three-dimensional (3D) multilayer OLEDs. Deposition without dissolving the underlying layer was realized by tuning the mixture ratio of the mixed solvents. A simulation of the electric force lines was used to assist in obtaining a uniform deposition on a 3D-curved substrate. The active layers of the OLED were sequentially prepared on watch glasses by the ESD technique. A green light emission from the concave device indicates that the ESD technique is a viable solution-processing technique for developing 3D multilayer OLEDs.

Emerging lighting and display technologies use phosphorescent organic light-emitting diodes (Ph-OLEDs) because they are thinner, more flexible, and less pixelated than their inorganic LED counterparts. While Ph-OLEDs can have an internal quantum efficiency of 100%, on metal electrodes the light-extraction efficiency is 5-30% primarily due to coupling to surface plasmon polariton (SPP) modes and photonic waveguide modes, SPPs, accounting for up to 50% of the loss in light-extraction efficiency. In addition to low light-extraction efficiency, efficiency roll-off in Ph-OLEDs is a significant cause of device degradation at high luminance and is due to triplet-polaron and triplet-triplet quenching processes. One way to address the efficiency roll-off issue is to accelerate the radiative decay rate of phosphorescence to reduce triplet quenching processes. Further, efficiency roll-off in blue Ph-OLEDs is very pronounced due to high triplet energies and significant triplet-polaron and triplet-triplet quenching relative to red and green Ph-OLED counterparts. This study aims to experimentally investigate the use of silver plasmonic nanostructured films with blue organic phosphorescent films to increase the radiative decay rate of triplet emission and, therefore, to minimize triplet quenching processes that cause unstable emission. We use the host poly(N-vinylcarbazole) (PVK) with the blue phosphorescent dopant, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) which is commonly-used in blue Ph-OLED prototypes. This host-dopant combination has been shown to improve light out coupling and enhance triplet excitation because the host assists in charge transport and excitation energy transfer, while the dopant provides color and increases intersystem crossing which improves the internal quantum efficiency. PVK:FIrpic thin film samples are spin coated onto planar silver, grating (1.6µm and 0.7µm), nanoporous (NPO) silver, and nanoparticle (NPT) silver. In addition PVK, FIrpic, and PVK:FIrpic thin films on glass are used as a reference. The silver plasmonic nanostructures are chosen due to their ability to increase light emission through light scattering. Each silver plasmonic nanostructure is prepared with 50 nm of silver using nanoimprint lithography deposition for grating (1.6µm and 0.7µm) and dewetting deposition for NPO and NPT. The samples are characterized using photoluminescence (PL) stability, PL lifetime, and PL quantum yield measurements to investigate the relationship between silver plasmonic nanostructures and improved phosphorescence stability. Preliminary data has shown a correlation between enhanced PL stability and PL lifetime of silver plasmonic nanostructures relative to a planar silver.

Two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) exhibit unique nonlinear optical (NLO) features and have becoming intriguing and promising candidate materials for photonic and optoelectronic devices with high performance and unique functions. Owing to layered geometry and the thickness-dependent bandgap, we studied the ultrafast NLO properties of a range of TMDCs. TMDCs with high-quality layered nanosheets were prepared through chemical vapor deposition (CVD) technique and vapor-phase growth method. Saturable absorption, two photon absorption (TPA) and two photon pumped frequency up-converted luminescence were observed from these 2D nanostructures. The exciting results open up the door to 2D photonic devices, such as passive mode-lockers, Q-switchers, optical limiters, light emitters, etc.

Variety of composite materials has been developed so far, but in many cases trade-off of the functions are of important issues: fabrication becomes difficult due to the significant increase of viscosity, and transparency of the polymer is sacrificed. To over come the trade off, controll of the nano-interface is the key, but nanoparticles are easily aggregated in polymer matrix because of the higher surface energy of NPs, and thus it has been considered a difficult task. Organic functionalization of inorganic nanoparticles is required to have higher affinity between NPs and polymers. The organic modification, NPs should be dispersed in an organic solvent with high concentration, which is difficult. For fabricating multi-functional materials, we proposed a new method to synthesize organic modified nanoparticles (NPs) in supercritical water. Since the organic molecules and metal salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic-inorganic conjugate nanoparticles can be synthesized under the condition. The hybrid NPs show high affinity with the organic solvent or the polymer matrix, which leads to fabricate the organic inorganic hybrid nanomaterials with the compatible (trade-off) functions.

The emergence of 3D printing technology in the past decade has set off a huge paradigm shift in manufacturing, which is termed as the fourth industrial revolution. In this context, two-photon stereolithography is poised to change the manufacturing at nano/micro scale. Generally, two-photon stereolithography is based on a photopolymerization reaction directly or indirectly initiated by a nonlinear optical molecule capable of simultaneously absorbing two-photons. When a near-infrared ultrashort-pulsed laser is closely focused into a volume of photoactive chemical medium (photoresist), real 3D microstructures can be fabricated using a layer-by-layer accumulating technique. In this lecture, high resolution patterns of polymers, ceramics, noble metals and semiconductors incorporated microstructures fabricated by two-photon-initiated polymerization will be presented. The 3D microstructures containing noble metals or semiconducting quantum dots are of great interest for applications in optoelectronics, photonics and biophotonics due to their ability to change the dielectric properties and refractive index of polymeric structures. In addition, recent developments of novel 3D cancer cell chips for the in vitro 3D cell growth simulation of tumor cells and the activity detection of anticancer drugs is also reported.

Publisher's note: This paper and conference presentation originally published on 21 February 2018, was withdrawn per author request.

Organic-inorganic hybrid perovskites with good intrinsic physical properties have received substantial interest for solar cell and optoelectronic applications. However, perovskite film always suffers from a low carrier mobility due to its structural imperfection including sharp grain boundaries and pinholes, restricting their device performance and application potential. Here we demonstrate a straightforward strategy based on multi-step annealing process to improve the performance of perovskite photodetector. Annealing temperature and duration greatly affects the surface morphology and optoelectrical properties of perovskites which determines the device property of phototransistor. The perovskite films treated with multi-step annealing method tend to form highly uniform, well-crystallized and high surface coverage perovskite film, which exhibit stronger ultraviolet-visible absorption and photoluminescence spectrum compare to the perovskites prepared by conventional one-step annealing process. The field-effect mobilities of perovskite photodetector treated by one-step direct annealing method shows mobility as 0.121 (0.062) cm²V^-1s^-1 for holes (electrons), which increases to 1.01 (0.54) cm²V^-1s^-1 for that treated with muti-step slow annealing method. Moreover, the perovskite phototransistors exhibit a fast photoresponse speed of 78 μs. In general, this work focuses on the influence of annealing methods on perovskite phototransistor, instead of obtains best parameters of it. These findings prove that Multi-step annealing methods is feasible to prepared high performance based photodetector.

The actuator is implemented based on the conductive polymer layer which causes photothermal conversion through the light in the near infrared region. The photothermally induced heat from conducting polymer can be converted into other type of energy such as mechanical, electrical or chemical energy. Especially, photothermal energy conversion into mechanical energy gives a unique method for reversible change of multi-layered actuator from 2-dimensional to 3-dimensional structure by thermal expansion coefficient mismatch among the layers. Herein we present the effect of the layer composition on the photoactuation and demonstrate a light switchable photothermal sensor.

Multi-scale (correlated quantum and statistical mechanics) modeling methods have been advanced and employed to guide the improvement of organic electro-optic (OEO) materials, including by analyzing electric field poling induced electro-optic activity in nanoscopic plasmonic-organic hybrid (POH) waveguide devices. The analysis of in-device electro-optic activity emphasizes the importance of considering both the details of intermolecular interactions within organic electro-optic materials and interactions at interfaces between OEO materials and device architectures. Dramatic improvement in electro-optic device performance--including voltage-length performance, bandwidth, energy efficiency, and lower optical losses have been realized. These improvements are critical to applications in telecommunications, computing, sensor technology, and metrology. Multi-scale modeling methods illustrate the complexity of improving the electro-optic activity of organic materials, including the necessity of considering the trade-off between improving poling-induced acentric order through chromophore modification and the reduction of chromophore number density associated with such modification. Computational simulations also emphasize the importance of developing chromophore modifications that serve multiple purposes including matrix hardening for enhanced thermal and photochemical stability, control of matrix dimensionality, influence on material viscoelasticity, improvement of chromophore molecular hyperpolarizability, control of material dielectric permittivity and index of refraction properties, and control of material conductance. Consideration of new device architectures is critical to the implementation of chipscale integration of electronics and photonics and achieving the high bandwidths for applications such as next generation (e.g., 5G) telecommunications.

Much work has been done developing and utilizing biomaterials over the last decade. Biomaterials not only includes deoxyribonucleic acid (DNA), but nucleobases and silk. These materials are abundant, inexpensive, non-fossil fuel-based and green. Researchers have demonstrated their potential to enhance the performance of organic and inorganic electronic and photonic devices, such as light emitting diodes, thin film transistors, capacitors, electromagnetic interference shielding and electro-optic modulators. Starting around the year 2000, with only a hand full of researchers, including researchers at the Air Force Research Laboratory (AFRL) and researchers at the Chitose Institute of Technology (CIST), it has grown into a large US, Asia and European consortium, producing over 3400 papers, three books, many book chapters and multiple patents. Presented here is a short overview of the progress in this exciting field of nano bio-engineering.

In this work, we synthesized temperature stable electro-optic (EO) polymers by post-functionalization technique. The EO polymer consists of high molecular hyperpolarizability chromophores and PMMA-based polymer with a high glass transition temperature. We attached chromophores to the high Tg polymers with controlling the loading concentrations. We found that the use of adamantly methacrylate enhanced the thermal resistance of the EO activity at elevated temperatures. We characterized synthesized EO polymers by using the size exclusion chromatography, UV-vis spectroscopy, and Tg analyzers. The thermal and temporal stability of the EO polymers were tested in the Mach-Zehnder interferometer waveguide modulators. The fabrication was based on our previous technique, resulting the measured Vp of around 2-4 V. The r33 of the waveguide corresponds to 60-80 pm/V at the wavelength of 1550 nm. We found the excellent thermal stability of the EO polymer modulator, showing little degradation of the EO activity under high temperature test at 105C for longer than 2000 hours. The results are attributed to the high Tg property of the synthesized EO polymers.

Plasmonics have been recognized as a promising platform that may premise the performance enhancement of diverse optoelectronics. Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. We first provide a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. It is noted that a universal paradigm to construct high-efficiency plasmonic solar cells with long term stability has not been established. Here, we propose a few strategies to develop viable plasmonic dye-sensitized solar cells and organic photovoltaic devices based on the integration of metal-graphene oxide core-shell nanostructures or lithographically-induced plasmonic nanopatterns. Very recently metal halide perovskites have been attractive as solar energy harvesters due to efficient ambipolar transport and strong light absorption. Metal halide perovskites have rapidly advanced thin film optoelectronic performance. We find that intercalation of larger alkylammonium between perovskite layers introduces quantitatively appreciable van der Waals interactions and drives improved material stability. Continuous tuning of the dimensionality, as assessed using photophysical studies, is achieved by the choice of stoichiometry in materials synthesis. We achieve the first certified hysteresis-free solar power conversion in a planar perovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity. The quasi-2D perovskites were also employed to develop limiting emitting diodes with the most bright and highest EQE. Lastly, combining the advance of plasmonic coupling and reduced-dimensionality perovskites, here we report plasmon-enhanced perovskites optoelectronic devices with a focus on thin-film photodectors and photovoltaic devices.

The polymer nanofiber carbon nanotube (CNT) based devices attracts attention since they promise high performance for next generation devices such as wearable electronics, ultra-light weighted appliances and foldable devices. This abstract describes the utilization of polymer nanofibers and CNT as major component of low cost foldable photo-resistor. We use polymer nanofiber as template guiding CNTs to generate nanocircuits and conductive sensing network. The controlled combination of CNTs and polymer nanofibers provide opportunities for device miniaturization without loss of performance. The nanofiber-CNT network based photo-resistor exhibits broad band response 400 to 1600 nm that holding promises for ultra-thin devices and new sensing platforms.

A class of small molecule donors configured in a donor-acceptor-acceptor’ (d-a-a’) structure have been studied for vacuum-deposited OPVs. They consist of an electron-donating (d) functional unit connected to two consecutive electron-accepting (a, a’) groups. The rigid and rod-like molecular backbones with strong push-pull interactions between the ‘d’ and ‘a’ units result in a large ground state dipole moment along the backbone axis. This leads to antiparallel π-π stacking that favors intermolecular charge transfer. In this work we synthesized two vacuum-deposited small molecules that are modified from previously reported donors with similar structures[1]. All molecules studied have the same molecular backbone with different side chains attaching to an asymmetric heterotetracene donor block. Single crystal analysis and thin film grazing incidence x-ray diffraction are performed. The donor with a shorter branched side chain yields the highest single crystal packing density, corresponding to the largest absorption coefficient and short circuit current (JSC) among the three molecules studied. The preferred face-on stacking arrangement that facilitates charge transport in the vertical direction also leads to a higher fill factor (FF). A power conversion efficiency of 9.3% is achieved with JSC = 16.5 mA/cm2, VOC = 0.94 V and FF = 0.60, which is one of the highest performance single junction OPVs grown by vacuum thermal evaporation. By relating the side chain shape with the crystal packing habit and the device performance, we provide a means of molecular structure modification leading to significant performance improvements. [1] X. Che, C.-L. Chung, X. Liu, S.-H. Chou, Y.-H. Liu, K.-T. Wong, S. R. Forrest, Advanced Materials 2016, 28, 8248.

Organic optoelectronic materials and devices are nowadays found in many devices such as smart phone displays or solar panels. The advantages of this already mature technology are clear: The large oscillator strengths of the materials enable bright and colorful, low-power displays with extremely high contrast or relatively high photo conversion efficiencies in solar cells while the fabrication costs tend to further decrease. However, organic optical sensors are not common in application although they would benefit from similar advantages but cannot compete with silicon detectors in the visible spectral range. However, in the near infrared (NIR) spectral region the situation is different: The standard inorganic material for detectors and LEDs is Indium-Gallium-Arsenide (InGaAs), which has many drawbacks: They are expensive due to epitaxial growth and contain reasonable amounts of highly toxic arsenic. We developed a new type of organic photovoltaic detector based on blends of electron accepting and donating molecules. We exploit the properties of the weakly absorbing charge transfer state formed at the donor-acceptor interface and combine the device with an optical microcavity. This allows us to spectrally-selective detect light up to 1600 nm. We show a prototype of a miniaturized spectrometer with basic calibration allowing for simple food screening applications and liquid analysis.

3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials.

Additive Manufacturing (AM) has the potential to become a powerful tool in the realization of complex optical components. The primary advantage that meets the eye, is that fabrication of geometrically complicated optical structures is made easier in AM as compared to the conventional fabrication methods (using molds for instance). But this is not the only degree of freedom that AM has to offer. With the multitude of materials suitable for AM in the market, it is possible to introduce functionality into the components one step before fabrication: by altering the raw material. A passive example would be to use materials with varying properties together, in a single manufacturing step, constructing samples with localized refractive indices for instance. An active approach is to blend in materials with distinct properties into the photopolymer resin and manufacturing with this composite material. Our research is currently focused in this direction, with the desired optical property to be introduced being Photoluminescence. Formation of nanocomposite mixtures to produce samples is the current approach. With this endeavor, new sensor systems can be realized, which may be used to measure the absorption spectra of biological samples. Thereby the sample compartment, the optics and the spectral light source (different quantum dots) are 3D-printed in one run. This component can be individually adapted to the biological sample with respect to wavelength, optical and mechanical properties.

Here we would like to present our work on the additive manufacturing of an active optical component. Based on the stereolithography method, a monolithic optical component was 3D-printed, showing light emission at different defined wavelengths due to UV excited quantum dots inside the 3D-printed optics.

In this work, the polymer was incorporated into the luminescent materials to form many encapsulated domains that could possible limit the forming of positive and negative charged layer inside each domain. This was expected to increase the luminescent area and hence the efficiency. Several polymers were used, including Poly(4-vinylphenol) (PVP), Poly (vinyl alcohol) (PVA), Poly (methyl methacrylate) (PMMA), Poly (ethylene Oxide) (PEO) and Poly(3,4- ethylenedioxythiophene) (PEDOT). To understand the effect of these polymers to the efficiency. The OLEC devices with Ru(bpy)₃(PF₆)₂, red-emitting materials, were made. Red light emitting was found in the OLEC devices with PVA, PMMA, and PEO polymer matrix. The highest efficacy of approximately 0.3 lm/W was obtained in the Ru (bpy)₃ OLEC with PEO as matrix, which is almost 100 times higher than the device with PVA as matrix. The reason of high luminescent efficiency was primary attributed to the low injection barrier for carrier from PEO into encapsulated Ru(bpy)₃(PF₆)₂. The result of this work indicates the forming of micro-encapsulated domain in the OLEC could enhance the luminous and the efficacy effectively.

Azobenzenes are widely used as light-responsive molecules in creating functional materials for applications ranging from non-linear optics to biotechnology. The light-sensitivity arises from the fully reversible light driven trans-cis-trans isomerization upon which the molecules exhibit large spectral and geometrical changes. Azobenzenes are often used as building blocks in self-assembling supramolecular materials. The self-assembly may strongly affect the isomerization dynamics of azobenzenes, especially the thermal half-life of the metastable cis-isomer. We show that the isomerization dynamics can be utilized to create a highly sensitive, optically readable relative humidity sensor. The optically active molecules, i.e. hydroxyazobenzene derivatives, are embedded into a poly(4‑vinylpyridine) matrix, where they are supramolecularly bound to the polymer chains. Environmental humidity causes intrinsic changes in the thermal isomerization mechanism of the hydroxyazobenzene molecules, and this leads to a large change in the cis-isomer lifetime. The cis-lifetime decreases exponentially up to 3 orders of magnitude with the change from 0 to 100 %RH. The lifetimes are stable and highly reproducible, which allows a high accuracy of the sensor. The supramolecular concept allows to embed a high concentration of the probe molecules into the polymer, while retaining amorphous structure within the thin film. This allows a thin sensing layer and a fast response to changes of relative humidity. Our new humidity sensing concept is fully integrable with optical fibres and by optimising the materials, it may be extended to sensing of also other hydrogen-bonding gases.

Degradation of organic semiconductors in the presence of oxygen is one of the bottlenecks preventing their wide-spread use in optoelectronic devices. The first step towards such degradation in functionalized pentacene (Pn) derivatives is formation of endoperoxide (EPO), which can either revert back to the parent molecule or proceed to molecule decomposition. We present the study of reversibility of EPO formation through probing the photophysical properties of functionalized fluorinated pentacene (Pn-R-F8) derivatives. Experiments are done in solutions and in films both at the single molecule level and in the bulk. In solutions, degradation of optical absorption and its partial recovery after thermolysis were quantified for various derivatives depending on the solvent. At the single molecule level, low concentrations of each type of molecules were imaged in a variety of polymer matrices at 633 nm excitation at room temperature in air using wide-field fluorescence microscopy. Fluorescence time trajectories were collected and statistically analyzed to quantify blinking due to reversible EPO formation depending on the host matrix. To understand the physical changes of the molecular system, a Monte Carlo method was used to create a multi-level simulation, which enabled us to relate the change in the molecular transition rates to the experimentally measured parameters. At the bulk level, photoluminescence decay due to photobleaching and recovery due to EPO reconversion were measured for the same derivatives incorporated into various matrices. These studies provide insight into the synergistic effect of the local nanoenvironment and molecular side groups on the oxygen-related degradation and subsequent recovery which is important for development of organic electronic devices.

Azobenzene derivatives in or bound to polymer show photoinduced birefringence and dichroism under polar light excitation through trans-cis isomerization and following reorientation of the molecules, sometimes being succeeded by macroscopic deformation as surface reliefs. In general, the transition process begins with the angular hole burning due to selective isomerization of the molecules aligned parallel to the light field, being followed by directionally random molecular reorientation in relaxation. As most of preceding studies were made with optical Kerr effect and four wave mixing, signal intensities reflected the difference between two index components and two regions, respectively, making it difficult to discriminate the temporal evolution of respective optical constant components. In this study, to elaborate the elementary processes, simple material system as DR1 doped PMMA was employed and in situ measurement of absorption spectrum and its polarization dependence were made under and after the excitation with linearly polarized light. The results indicated that the absorbance reduced strongly when the probe light was parallel to the pump, and that in perpendicular direction it also reduced with one-thirds amount of the counterpart. It showed that the angular hole burning process was dominant and reorientation effect made less contribution to the dichroism, contrary to common understanding. Estimation of extinction coefficient modulation caused by both mechanisms was made based on a simple model. Quantum efficiency of photoisomerization, longtime stability, dye concentration dependence, comparison to induced birefringence, and comparison between doped polymer and side chain polymer will be discussed.

Measuring circular dichroism in time-resolved experiments is very promising to investigate the dynamics of conformational changes occurring in chemical or biological processes. This is however very challenging because of the weakness of the signals. Here we present several complementary set-ups which allow us to investigate changes in CD on a large range of timescales, from picoseconds to milliseconds. These set-ups are utilized to probe (i) the dynamics of the dihedral angle in Binaphthol following photoexcitation, (ii) the first step in the photoisomerization process in Photoactive Yellow Protein, and (iii) folding/unfolding processes of DNA G-quadruplexes.

Near-infrared high-sensitivity photodetectors are the key component of wearable optical systems for noninvasive physiological monitoring, such as photoplethysmography (PPG) and near-infrared spectroscopy. Compared to the high-voltage driven avalanche photodiodes and photomultipliers, organic phototransistors based on a bulk heterojunction (BHJ) structure have a set of unique advantages including self-amplification (via a photoconductive gain mechanism), low operation voltage, lightweight, flexible, printable and CMOS compatible. By employing a bilayer dielectric design and an ultrathin encapsulation structure, we have realized a flexible/epidermal low-voltage (< 3V) driven BHJ phototransistor with ultra-high responsivity (3.5 ×10^5 AW^-1) and low noise equivalent power (1.2 × 10^−15 W Hz^−1/2). We combined the phototransistor with a high-efficiency III-V LED to realize a hybrid PPG sensor and demonstrated low-power and high stability continuous tracking of heart rate variability and pulse pressure. To reveal the fundamental correlations between the heterojunction morphology and the device’s figures-of-merits, such as responsivity, operation bandwidth, and noise, we carried out a systematical investigation combining morphological characterizations with photo-physics and charge transport studies. The results highlight the importance of optimizing interface charge separation and bulk charge transport through morphology control. This study not only reveals the physical mechanisms that govern the operation of organic phototransistors but also provides know-hows to realize highly flexible and stable photodetection systems.

A facile approach enhancing electron extraction in zinc oxide (ZnO) electron transfer interlayer and improving performance of bulk-heterojunction (BHJ) polymer solar cells (PSCs) by adding cetyltrimethylammonium bromide (CTAB) into sol-gel ZnO precursor solution was demonstrated in this work. The power conversion efficiency (PCE) has a 24.1% increment after modification. Our results show that CTAB can dramatically influence optical, electrical and morphological properties of ZnO electron transfer layer, and work as effective additive to enhance the performance of bulk- heterojunction polymer solar cells.

The exceptional photovoltaic properties demonstrated for organic-inorganic hybrid lead halide perovskites have attracted tremendous attention around the world. The intriguing optoelectrical characteristics include strong absorption coefficient, high carrier mobility and long charge diffusion length. The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have now been boosted up to a certified 22.7% within a few years. Based on ambipolar type carrier transport properties of the perovskites, hole-conductor-free (HTMfree) PSCs have been developed, which simplifies the configuration of the devices. Previously, our group has developed a carbon based HTM-free printable mesoscopic PSC and achieved a certified PCE of 12.8 % with high stability. Herein, we reported a new hybrid carbon electrode based on ultrathin graphite/carbon black for HTM-free printable mesoscopic PSCs, and obtained a PCE of 13.83%.

We have recently reported that by sending a tightly collimated (0.05 - 2 mm diameter) red- or near-IR laser beam through an aqueous solution of pseudoisocyanine (PIC) J-aggregates, a macroscopic tube-like structure is formed surrounding the laser beam on the time scale of minutes. This self-assembled structure is comprised of heterogeneous material containing micrometer-size rod-like strands or microcrystals. Because the illumination wavelength is far redshifted from the linear absorption range of the PIC and J-aggregates, the self-assembly is likely induced by some very weak background absorption or dissipation. Furthermore, strong correlation of the effect with the characteristic Jaggregate peak in the absorption spectrum and critical dependence of the “tube” formation on pH of the solution indicate molecular charge related non-equilibrium nature of the underlying mechanism. Most interestingly, the structure formation is accompanied by strongly polarized scattering. When observed between crossed polarizers, the angular intensity distribution of the scattered light resembles Maltese cross figure, indicating that the scattering rods are arranged in a circular pattern around the beam axis direction. It appears that the illumination is creating in the medium a radially directed gradient of either concentration-, temperature- or other type of parameter that controls the microcrystal formation.

This report describes change in the characteristics of vapor deposition films for bis-styrylbenzene derivatives (BSDs) after thermal treatment. The compounds employed in the present study were trifluoromethyl-group substituted BSDs: E,E-1,4- bis(2-trifluoromethylstyryl)benzene, (2-CF3), E,E-1,4-bis(3-trifluoromethylstyryl)benzene, (3-CF3), and E,E-1,4-bis(4- trifluoromethylstyryl)benzene, (4-CF3). The fluorescence spectra and the morphologies of the evaporated films of 2-CF3 changed depending on the thermal treatment temperature. As-evaporated film was aggregation of micron size crystalline domains. After thermal treatment at 100°C for 30 min, these changed into a long rectangular parallelepiped crystals suggesting that structural order has increased. Meanwhile, the optical properties and crystalline structures of the evaporated 3-CF3 films did not change even after thermal treatment at 110°C for 30 min. In the case of 4-CF3, the fluorescence spectrum of the evaporated film shifted to the shorter wavelength side after the thermal treatment. From the results of X-ray diffraction, the evaporated film showing crystallinity decreased in the structure orderliness by thermal treatment at 170°C for 30 min.

Degenerate instantaneous two-photon absorption (2PA) cross section and 2PA spectrum measurements were used to determine the molecular electric dipole change in the metal-to-ligand charge-transfer transition of ruthenium(II) triscomplexes of 2,2’-bipyridine and 1,10-phenanthroline ligands. Comparison between the 2PA and one-photon absorption (1PA) spectra indicate that the phenanthroline complex has D3 symmetry in the ground state, while the bipyridine complex has its symmetry lowered. The high accuracy of the nonlinear cross section measurements was achieved by means of improved 2PA reference standards, and the dipole change was evaluated using the two essential states model of 2PA applied in the lowest-energy transitions. We demonstrate that quantitative 2PA spectroscopy is a viable alternative to standard methods used to estimate change of molecular dipole moment, and is uniquely informative of the effects of different solvents and local environments on the absorber.

A novel low power design for polymeric Electro-Optic reflection modulator is proposed based on the Extraordinary Reflection of light from multilayer structure consisting of a plasmonic metasurface with a periodic structure of sub wavelength circular apertures in a gold film above a thin layer of EO polymer and above another thin gold layer. The interference of the different reflected beams from different layer construct the modulated beam, The applied input driving voltage change the polymer refractive index which in turn determine whether the interference is constructive or destructive, so both phase and intensity modulation could be achieved. The resonant wavelength is tuned to the standard telecommunication wavelength 1.55μm, at this wavelength the reflection is minimum, while the absorption is maximum due to plasmonic resonance (PR) and the coupling between the incident light and the plasmonic metasurface.