Showing papers in "Journal of Photonics for Energy in 2016"
TL;DR: In this article, the authors review major advances in perovskite solar cells that have contributed to the recent efficiency enhancements, including the evolution of device architecture, the development of material deposition processes, and the advanced device engineering techniques aiming to improve control over morphology, crystallinity, composition, and interface properties of the perovsite thin films.
Abstract: Organo-metal halide perovskite–based solar cells have been the focus of intense research over the past five years, and power conversion efficiencies have rapidly been improved from 3.8 to >21%. This article reviews major advances in perovskite solar cells that have contributed to the recent efficiency enhancements, including the evolution of device architecture, the development of material deposition processes, and the advanced device engineering techniques aiming to improve control over morphology, crystallinity, composition, and the interface properties of the perovskite thin films. The challenges and future directions for perovskite solar cell research and development are also discussed.
222 citations
TL;DR: In this article, the authors present the current state of research in spinel ferrites as photoelectrode materials for PECs application and present strategies to improve energy conversion efficiency.
Abstract: Solar-assisted water splitting using photoelectrochemical cells (PECs) is one of the promising pathways for the production of hydrogen for renewable energy storage. The nature of the semiconductor material is the primary factor that controls the overall energy conversion efficiency. Finding semiconductor materials with appropriate semiconducting properties (stability, efficient charge separation and transport, abundant, visible light absorption) is still a challenge for developing materials for solar water splitting. Owing to the suitable bandgap for visible light harvesting and the abundance of iron-based oxide semiconductors, they are promising candidates for PECs and have received much research attention. Spinel ferrites are subclasses of iron oxides derived from the classical magnetite (FeIIFe2IIIO4) in which the FeII is replaced by one (some cases two) additional divalent metals. They are generally denoted as MxFe3−xO4 (M=Ca, Mg, Zn, Co, Ni, Mn, and so on) and mostly crystallize in spinel or inverse spinel structures. In this mini review, we present the current state of research in spinel ferrites as photoelectrode materials for PECs application. Strategies to improve energy conversion efficiency (nanostructuring, surface modification, and heterostructuring) will be presented. Furthermore, theoretical findings related to the electronic structure, bandgap, and magnetic properties will be presented and compared with experimental results.
108 citations
TL;DR: This review gives a concise overview of the unassisted PEC devices with some state-of-the-art progress toward efficient P EC devices for future sustainable solar energy utilization.
Abstract: Photoelectrochemical (PEC) energy conversion systems have been considered as a highly potential strategy for clean solar fuel production, simultaneously addressing the energy and environment challenges we are facing. Tremendous research efforts have been made to design and develop feasible unassisted PEC systems that can efficiently split water into hydrogen (H2) and oxygen with only the energy input of sunlight. A fundamental understanding of the concepts involved in PEC water splitting and energy conversion efficiency enhancement for solar fuel production is important for better system design. This review gives a concise overview of the unassisted PEC devices with some state-of-the-art progress toward efficient PEC devices for future sustainable solar energy utilization.
77 citations
TL;DR: The thermal activated delayed fluorescence (TADF) is an emerging hot topic as mentioned in this paper and has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence.
Abstract: Thermally activated delayed fluorescence (TADF) is an emerging hot topic. Even though this photophysical mechanism itself has been described more than 50 years ago and optoelectronic devices with organic matter have been studied, improved, and even commercialized for decades now, the realization of the potential of TADF organic light-emitting diodes (OLEDs) happened only recently. TADF has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence. In this review, the TADF concept is introduced in terms that are also understandable for nonchemists. The basic concepts behind this mechanism as well as state-of-the-art examples are discussed. In addition, the future economic impact, especially for the lighting and display market, is addressed here. We conclude that TADF materials are especially helpful to realize efficient, durable deep blue and white displays.
69 citations
TL;DR: In this paper, a review of self-assembled QD solar cells and colloidal QDSCs is presented, with a focus on understanding carrier dynamics and suppression of a reduction of open circuit voltage.
Abstract: Semiconductor quantum dots (QDs) have a potential to increase the power conversion efficiency in photovoltaic operation because of the enhancement of photoexcitation. Recent advances in self-assembled QD solar cells (QDSCs) and colloidal QDSCs are reviewed, with a focus on understanding carrier dynamics. For intermediate-band solar cells using self-assembled QDs, suppression of a reduction of open circuit voltage presents challenges for further efficiency improvement. This reduction mechanism is discussed based on recent reports. In QD sensitized cells and QD heterojunction cells using colloidal QDs well-controlled heterointerface and surface passivation are key issues for enhancement of photovoltaic performances. The improved performances of colloidal QDSCs are presented.
62 citations
TL;DR: In this article, a review provides a collective view of recent developments made in the synthesis of Cs-LHQDs and their properties and their potential use for light emitting diodes, photodetectors and lasers.
Abstract: Metal halide-based perovskite quantum dots (QDs) have emerged as promising materials for optoelectronics and future energy applications Among them, cesium lead halide-based perovskite quantum dots (Cs-LHQDs) have been found to be potential luminescent candidates and alternatives for the II–VI and I−III−VI2 groups semiconductor nanoparticles These perovskites provide an excellent quantum yield (90%) larger than any other semiconductor QDs At present, synthesis of Cs-LHQDs has been successfully achieved through a traditional colloidal-based hot-injection method and a room temperature precipitation method Some of the interesting results in their structural, optical, and morphological properties are being analyzed to understand their energy-transfer mechanism in the colloidal state Morphology of nanoplates, nanowires, nanocube, and nanosheets in these materials confirms their physical parameters-dependent self-assembly nature in a colloidal medium Their potential use for light emitting diodes, photodetectors, and lasers is also highly motivated This review provides a collective view of recent developments made in the synthesis of Cs-LHQDs and their properties
61 citations
TL;DR: In this paper, the fastest hydrogen evolution during metal deposition was observed for copper deposited on premodified DAP with silver (DAP/Ag/Cu), probably due to partial coverage of silver with fine clusters of Cu and thus facilitation of proton adsorption and reduction on well-dispersed Cu nanoclusters.
Abstract: Decahedral anatase particles (DAPs) with eight equivalent (101) facets and two (001) facets were prepared by the gas-phase process. Monometallic and bimetallic photocatalysts were prepared by photodeposition of silver and copper on DAP. It was found that the method of metal deposition (sequential/simultaneous) is crucial for resultant properties and thus for photocatalytic performance. The fastest hydrogen evolution during metal deposition was observed for copper deposited on premodified DAP with silver (DAP/Ag/Cu), probably due to partial coverage of silver with fine clusters of Cu and thus facilitation of proton adsorption and reduction on well-dispersed Cu nanoclusters. Although DAP/Ag/Cu exhibited the fastest rate of hydrogen evolution, single-modified DAP with silver exhibited the best performance for oxidative decomposition of organic compounds under vis irradiation.
44 citations
TL;DR: In this paper, an effective electron transport material, namely chemical bath deposited cadmium sulphide (CdS) film under low temperature, was used in perovskite-based solar cells.
Abstract: Planar heterojunction perovskite solar cell is one of the most competitive photovoltaic technologies, while charge transport materials play a crucial role. We successfully demonstrated an effective electron transport material, namely chemical bath deposited cadmium sulphide (CdS) film under low temperature, in perovskite-based solar cells. Power conversion efficiency of 16.1% has been achieved, which is comparable to that of devices based on TiO2 film prepared via low-temperature processes. Electronic impedance spectra reveal that the CdS-based device presents a higher recombination resistance than TiO2-based devices, which reduces carrier recombination and increases the open circuit voltage. The interface between CdS and perovskite was characterized with improved characteristics when compared to TiO2, e.g., efficient carrier extraction and reduced surface defect–associated degradation in the devices, which help to alleviate anomalous hysteresis and long-term instability. Furthermore, the entire device was fabricated via solution process with a processing temperature below 100°C, suggesting a promising method of further development of perovskite solar cells and commercial manufacturing.
31 citations
TL;DR: It is shown that beyond the sole optical properties, such additional elements can simultaneously improve the electrical characteristics of solution-processed OLEDs, and thus enable an optimization of the devices at different levels.
Abstract: To allow a greater acceptance in the display and lighting markets, organic light-emitting diode (OLED) technology is currently the subject of intensive research efforts aimed at manufacturing cost-effective devices with higher efficiencies. In this regard, strategies matured in the field of photonics and nanophotonics can be applied for photon management purposes to improve the outcoupling of the generated light and to control the emission pattern. In this review, we report on the recent experimental and numerical advances to pursue those goals by highlighting the example of bottom-emitting devices. The cases of periodical micro- and nanostructures, as well as of stochastic ensembles that can be easily implemented using printing techniques, are covered herein. It is shown that beyond the sole optical properties, such additional elements can simultaneously improve the electrical characteristics of solution-processed OLEDs, and thus enable an optimization of the devices at different levels.
30 citations
TL;DR: In this article, the authors used numerical simulation and observed that more than 20% device efficiency can be obtained if defect density of the photosensitive material remains lower than 4×1014 cm−3 and thickness 400nm or more.
Abstract: A methyl ammonium lead iodide (H3NH3PbI3)-based solar cell can have photovoltaic conversion efficiency of more than 20%, primarily because the material shows lower defect density, high carrier mobility-lifetime, and broader absorption spectra. A further improvement in device efficiency can be obtained using light capture and trapping schemes, with textured front surface and back reflector. In order to understand characteristic performance of the device, we used numerical simulation and observed that more than 20% device efficiency can be obtained if defect density of the photosensitive material remains lower than 4×1014 cm−3 and thickness 400 nm or more. Investigation of light trapping scheme shows that the current density (Jsc) can be raised with this scheme, but the most effective increase in the Jsc can be observed for 97-nm thick active layers. Reverse saturation current density of these cells that may be directly related to recombination loss of photogenerated carriers, remains low, but increases linearly with the defect density. A tandem cell with pyramidally textured front surface was investigated with such a perovskite-based top cell and Si heterojunction bottom cell; it shows an efficiency of as high as 29.5%.
24 citations
TL;DR: In this article, a two-dimensional finite-element model was developed to simulate the optoelec- tronic performance of thin-film, p-i-n junction solar cells, where semiconductor layers were made from mixtures of two different alloys of hydrogenated amorphous silicon; empirical relation ships between the complex-valued relative optical permittivity and the bandgap were used.
Abstract: A two-dimensional finite-element model was developed to simulate the optoelec- tronic performance of thin-film, p-i-n junction solar cells. One or three p-i-n junctions filled the region between the front window and back reflector; semiconductor layers were made from mixtures of two different alloys of hydrogenated amorphous silicon; empirical relation- ships between the complex-valued relative optical permittivity and the bandgap were used; a transparent-conducting-oxide layer was attached to the front surface of the solar cell; and a metallic reflector, either flat or periodically corrugated, was attached to the back surface. First, frequency-domain Maxwell postulates were solved to determine the spatial absorption of photons and thus the generation of electron-hole pairs. The AM1.5G solar spec- trum was taken to represent the incident solar flux. Second, drift-diffusion equations were solved for the steady-state electron and hole densities. Numerical results indicate that increasing the number of p-i-n junctions from one to three may increase the solar-cell efficiency by up to 14%. In the case of single p-i-n junction solar cells, our simulations indicate that efficiency may be increased by up to 17% by incorporating a periodically corrugated back reflector (as opposed to a flat back reflector) and by tailoring the bandgap profile in the i layer. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original pub- lication, including its DOI. (DOI: 10.1117/1.JPE.6.025502)
TL;DR: In this article, the effect of UV light on sorption kinetics and resistive gas/vapor response of different CNT networks, films of semiconducting single-wall nanotubes (s-SWNTs), metallic single-walled nanotube, and multi-wall CNTs were exposed to O2 and H2O vapor in the dark and under UV irradiation.
Abstract: Interaction between ultraviolet (UV) light and carbon nanotube (CNT) networks plays a central role in gas adsorption, sensor sensitivity, and stability of CNT-based electronic devices. To determine the effect of UV light on sorption kinetics and resistive gas/vapor response of different CNT networks, films of semiconducting single-wall nanotubes (s-SWNTs), metallic single-wall nanotubes, and multiwall nanotubes were exposed to O2 and H2O vapor in the dark and under UV irradiation. Changes in film resistance and mass were measured in situ. In the dark, resistance of metallic nanotube networks increases in the presence of O2 and H2O, whereas resistance of s-SWNT networks decreases. UV irradiation decreases the resistance of metallic nanotube networks in the presence of O2 and H2O and increases the gas/vapor sensitivity of s-SWNT networks by nearly a factor of 2 compared to metallic nanotube networks. s-SWNT networks show evidence of delamination from the gold-plated quartz crystal microbalance crystal, possibly due to preferential adsorption of O2 and H2O on gold. UV irradiation increases the sensitivity of all CNT networks to O2 and H2O by an order of magnitude, which demonstrates the importance of UV light for enhancing response and lowering detection limits in CNT-based gas/vapor sensors.
TL;DR: In this paper, two nanocomposite photocatalysts were synthesized by forming highly dispersed Cu sites on TiO2 surfaces, and the synthesized materials were characterized with microscopy, UV-visible, and infrared spectroscopy.
Abstract: Two nanocomposite photocatalysts were synthesized by forming highly dispersed Cu sites on TiO2 surfaces. The synthesized materials were characterized with microscopy, UV-visible, and infrared spectroscopy, and tested in photocatalytic CO2 reduction. Computational modeling was conducted to elucidate the role of single Cu sites in promoting CO2 reduction on TiO2. The nanocomposites demonstrated significantly higher activity than bare TiO2 in photocatalysis, and the activity was found to be related to the chemical state of surface Cu+ species. According to our modeling studies, the highly dispersed Cu sites likely contributed to the improved photocatalysis by stabilizing surface adsorption of CO2 on TiO2. Our experimental and modeling studies further confirmed the direct involvement of surface Cu sites in CO generation via CO2 reduction.
TL;DR: In this paper, a single-step ultrasonic substrate vibration posttreatment (SVPT) was used to improve the mixing and homogeneity of the wet spun-on PEDOT:PSS films.
Abstract: Organic solar cells are usually nonreproducible due to the presence of defects in the structure of their constituting thin films To minimize the density of pinholes and defects in PEDOT:PSS, which is the hole transporting layer of a standard polymer solar cell, ie, glass/ITO/PEDOT:PSS/P3HT:PCBM/Al, and to reduce scattering in device performance, wet spun-on PEDOT:PSS films are subjected to imposed ultrasonic substrate vibration posttreatment (SVPT) The imposed vibration improves the mixing and homogeneity of the wet spun-on films, and consequently the nanostructure of the ensuing thin solid films For instance, our results show that by using the SVPT, which is a mechanical, single-step and low-cost process, the average power conversion efficiency of 14 identical cells increases by 25% and the standard deviation decreases by 22% indicating that the device photovoltaic performance becomes more consistent and significantly improved This eliminates several tedious and expensive chemical and thermal treatments currently performed to improve the cell reproducibility
TL;DR: The tunable and amazing properties of plasmonic nanostructures have received significant attentions in the fields of solar energy conversion as discussed by the authors, and they can also serve as economical electrodes for high-efficient carrier collection.
Abstract: The tunable and amazing properties of plasmonic nanostructures have received significant attentions in the fields of solar energy conversion. Plasmonic nanostructures provide pathways to directly convert solar energy into electric energy by hot-carrier generation. They can also serve as economical electrodes for high-efficient carrier collection. Both have promising potential for manufacturing new generation solar cells. Here, we review recent advances in plasmonic nanostructures for electronic designs of photovoltaic devices and specially focus on plasmonic hot-carrier photovoltaic architectures and plasmonic electrode structures. Technical challenges toward low-cost and high-performance plasmonics-based solar cells are also discussed.
TL;DR: In this paper, the intersection of nanophotonics, materials such as photonic crystals (PC), but also irregular templated light scattering interfaces, with their application to solar fuels photocatalysis is discussed.
Abstract: We cover the intersection of nanophotonics, materials such as photonic crystals (PC), but also irregular templated light scattering interfaces, with their application to solar fuels photocatalysis. We describe the fundamental principles of adapting nanophotonics to photocatalysis, particularly slow photon effects and how appropriate choice of stop band and edge position of the PC can be exploited for light harvesting. We also review several representative examples of nanophotonic design applied to photocatalytic semiconductor materials. We include the most heavily investigated photocatalytic materials (such as TiO2), as well as inherently visible light active semiconductors, and materials sensitized with semiconductor nanocrystals or plasmonic metal nanoparticles. Finally, we review alternative scattering interfaces useful for improving the performance of solar fuels photocatalysis.
TL;DR: In this paper, the operating principles behind surface plasmon photodetectors based on the internal photoelectric effect are reviewed and compared, and the most recent and leading edge concepts reported in the literature are surveyed and compared.
Abstract: Surface plasmon photodetectors are of broad interest They are promising for several applications including telecommunications, photovoltaic solar cells, photocatalysis, color-sensitive detection, and sensing, as they can provide highly enhanced fields and strong confinement (to subwavelength scales) Such photodetectors typically combine a nanometallic structure that supports surface plasmons with a photodetection structure based on internal photoemission or electron–hole pair creation Photodetector architectures are highly varied, including waveguides, gratings, nanoparticles, nanoislands, or nanoantennas We review the operating principles behind surface plasmon photodetectors based on the internal photoelectric effect, and we survey and compare the most recent and leading edge concepts reported in the literature
TL;DR: In this paper, the spectral spectral properties of generalized Thue-Morse photonic structures (GTM) were theoretically investigated, where n and m are both positive integers representing parameters of GTM sequence and k is the order of this sequence.
Abstract: We theoretically investigate the spectral of light-localization in one-dimensional generalized Thue–Morse (GTM) photonic structures (n,m,k), where n and m are both positive integers representing parameters of GTM sequence and k is the order of this sequence. Numerical analysis is performed by the transfer matrix method algorithm to investigate their optical properties. We have shown that by varying m and n simultaneously, the electric field intensity in the GTM structure varies according to the parity of these parameters and also according to the peak positions.
TL;DR: In this article, Auger-electron-stimulated organic light-emitting diodes (OLEDs) have been shown to operate under high bias voltages at, or above, the highest occupied molecular orbital (HOMO) energy gaps of the light emitting molecules.
Abstract: Organic light-emitting diodes (OLEDs) have numerous applications ranging from flat-panel displays to eco-friendly solid-state lightings. OLEDs typically operate under high bias voltages at, or above, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gaps of the light-emitting molecules. We review recent development in Auger-electron-stimulated OLEDs, which have working voltages below the HOMO–LUMO energy gaps of emitters; i.e., the output photon energies are higher than the input electrical energies.
TL;DR: In this article, the authors analyzed the voltage and frequency dependence of three types of Seebeck nano-antennas and found that the square spiral antenna has the widest bandwidth and the highest induced current of the three analyzed geometries.
Abstract: Seebeck nanoantennas, which are based on the thermoelectric effect, have been proposed for electromagnetic energy harvesting and infrared detection. The responsivity and frequency dependence of three types of Seebeck nanoantennas is obtained by electromagnetic simulation for different materials. Results show that the square spiral antenna has the widest bandwidth and the highest induced current of the three analyzed geometries. However, the geometry that presented the highest temperature gradient was the bowtie antenna, which favors the thermoelectric effect in a Seebeck nanoantenna. The results also show that these types of devices can present a voltage responsivity as high as 36 μV/W for titanium–nickel dipoles resonant at far-infrared wavelengths.
TL;DR: In this paper, the authors explored the limits of photocatalytic water oxidation activity with iron (III) oxide hydroxide nanocrystals and NaIO4 as a sacrificial electron acceptor.
Abstract: Hematite has attracted considerable interest as a photoanode material for water oxidation under visible illumination. Here, we explore the limits of photocatalytic water oxidation activity with iron (III) oxide hydroxide nanocrystals and NaIO4 as a sacrificial electron acceptor (E=1.63 V NHE at pH=0.5). The sol was prepared by hydrolysis of FeCl3 in boiling 0.002-M HCl solution and confirmed to mainly consist of s-FeO(OH) (akaganeite) particles with 5 to 15 nm diameter. From a 0.01 M aqueous NaIO4 solution, the sol evolves between 4.5 and 35.2 μmolO2 h−1, depending on pH, light intensity (>400 nm, 290 to 700 mW cm−2), s-FeO(OH), and NaIO4 concentration. The activity increases with pH, and depends linearly on light intensity and photocatalyst amount, and it varies with sacrificial electron donor concentration. Under optimized conditions, the apparent quantum efficiency is 0.19% (at 400 nm and 460 mW cm−2), and the turnover number is 2.58 based on total s-FeO(OH). Overall, the efficiency of the s-FeO(OH)/NaIO4 photocatalytic system is limited by electron hole recombination and by particle aggregation over longer irradiation times (24 h). Lastly, surface photovoltage measurements on s-FeO(OH) films on fluorine doped tin oxide substrate confirm a 2.15 eV effective band gap for the material.
TL;DR: In this article, a comparative study of two-sided nanopyramidal structures for photovoltaic applications was conducted. And the results showed that both of the ultrathin silicon with front nanopyramids and rear silver nano-arrays and the two-side nano-ramids are promising for photoprocessor applications.
Abstract: Ultrathin crystalline silicon wafers for photovoltaic applications have attracted intensive attention because of potential benefits in cost-effectiveness. Structural design with high light absorption is important for photovoltaics because planar ultrathin silicon is poor in absorption. We conduct a comparative investigation on designs of light absorption enhancement for 2-μm-thick ultrathin crystalline silicon, where the front texture is a nanopyramidal structure and the rear adopts several designs. Our calculation results show that both of the ultrathin silicon with front nanopyramids and rear silver nanoarrays and the ultrathin silicon with two-sided nanopyramids are promising for photovoltaic applications. For the latter design, the calculated photocurrent achieves the highest value of 35.1 mA/cm2 when a perfect electric conductor layer is applied at the bottom. In contrast, the former design has a lower photocurrent value of 31.2 mA/cm2. But, this design is of practical significance because the majority of experimental reports on ultrathin crystalline silicon solar cells are single-sided front-textured at present and the fabrication techniques of plasmonic Ag nanoarrays are matured. Compared with previous reports, the present work offers a multiple option of structural designs for ultrathin crystalline silicon to enhance the light absorption for photovoltaic applications.
TL;DR: In this article, an optimized luminescent solar concentrator (LSC) based on the combination of different organic dyes as luminecent species and silicon solar cells was presented, aiming at the highest photon collection at the edges of the LSC plate under a solar AM1.5G spectrum.
Abstract: We present an optimized luminescent solar concentrator (LSC) based on the combination of different organic dyes as luminescent species and silicon solar cells. As a first part of this work, a deep screening of organic dyes used since the 1980s in LSC research has been performed and 14 of them have been chosen and characterized in a polymethyl methacrylate (PMMA) host at a fixed concentration (1%). Departing from this initial study, an empirical optimization procedure has been implemented, aiming the highest photon collection at the edges of the LSC plate under a solar AM1.5G spectrum. An optimal three-dye system has been selected in order to achieve a high absorption range over the uv–vis spectrum. The incorporation of these molecules in the PMMA host has been made following two different strategies: (i) the stacking of three individual LSC plates (one dye in each) and (ii) the merging of three organic dyes in a single LSC plate allowing Forster resonance energy transfer (FRET) to occur. In addition, PMMA bulk and thin film on glass plates have been manufactured considering stacking and FRET strategies. Finally, a bulk FRET-based LSC has been manufactured and its optical and electrical performance evaluated and compared to the best reported values used for LSC characterization. To the best of our knowledge, our LSC possesses the highest reported concentration (C=0.80), surpassing Slooff et al. (C=0.73).
TL;DR: In this paper, a green synthesis of nanoparticles (NPs) was used to manufacture gold NPs in water using a Ti:Sapphire laser with 30-fs FWHM pulses, 800-nm mean wavelength, and 1-kHz repetition rate.
Abstract: A laser-based “green” synthesis of nanoparticles (NPs) was used to manufacture gold NPs in water. The light source is a Ti:Sapphire laser with 30 fs FWHM pulses, 800 nm mean wavelength, and 1 kHz repetition rate. The method involves two stages: (1) pulsed laser ablation in liquids and (2) photo-fragmentation (PF). Highly pure and well-dispersed NPs with a diameter of 18.5 nm that can be stored at room temperature without showing any agglomeration over a period of at least 3 months were produced without the need to use any stabilizer. Transmittance spectra, extinction coefficient, NPs agglomeration dynamics, and thermal conductivity of the nanofluids obtained were analyzed before and after being submitted to thermal cycling and compared to those obtained for commercial gold/water suspensions. Optical properties have also been investigated, showing no substantial differences for thermal applications between NPs produced by the laser ablation and PF technique and commercial NPs. Therefore, nanofluids produced by this technique can be used in thermal applications, which are foreseen for conventional nanofluids, e.g., heat transfer enhancement and solar radiation direct absorption, but offering the opportunity to produce them in situ in almost any kind of fluid without the production of any chemical waste.
TL;DR: In this paper, a hybrid solar simulator with the spectral match beyond class A is proposed, where six types of high-power light-emitting diodes (LEDs) and tungsten halogen lamps in total were employed to obtain spectral match with deviation from the standardized one in twelve spectral ranges between 400 and 1100 nm.
Abstract: A compact hybrid solar simulator with the spectral match beyond class A is proposed. Six types of high-power light-emitting diodes (LEDs) and tungsten halogen lamps in total were employed to obtain spectral match with deviation from the standardized one in twelve spectral ranges between 400 and 1100 nm. All spectral ranges were twice as narrow than required by IEC 60904-9 Ed.2.0 and ASTM E927-10(2015) standards. Nonuniformity of the irradiance was evaluated and deviation from the average value of the irradiance (corresponding to A class nonuniformity) can be obtained for the area of >3-cm diameter. A theoretical analysis was performed to evaluate possible performance of our simulator in the case of GaInP/GaAs/GaInAsP/GaInAs four-junction tandem solar cells and AM1.5D (ASTM G173-03 standard) spectrum. Lack of ultraviolet radiation in comparison to standard spectrum leads to 6.94% reduction of short-circuit current, which could be remedied with 137% increase of the output from blue LEDs. Excess of infrared radiation from halogen lamps outside ranges specified by standards is expected to lead to ∼0.77% voltage increase.
TL;DR: In this article, the surface morphological, optical, structural, and electrical properties of Ag-ZnO thin film were investigated by various characterization techniques, and the improvement of ultraviolet photodetection was attributed to the surface plasmon effect using Ag nanodisks.
Abstract: In this work, we present the enhancement of ultraviolet (UV) photodetection of Ag-ZnO thin film deposited by radio frequency magnetron sputtering. The surface morphological, optical, structural, and electrical properties of the deposited thin films were investigated by various characterization techniques. With this Ag-ZnO thin film structure and proper geometry of metal–semiconductor–metal (MSM) interdigitated structure design, photocurrent enhancement has been accomplished. MSM-photodetectors (PDs) using structures of Ag-ZnO gave a 30 times higher magnitude photocurrent at 340 nm of the wavelength. Plasmon-induced hot electrons contributed to improved spectral response to the UV region, while absorption and scattering effect enhanced broadband improvement to a response in the VIS–IR spectrum range. The improvement of Ag-ZnO PD in comparison with ZnO is attributed to the surface plasmon effect using Ag nanodisks. These results indicate that Ag-ZnO thin films can serve as excellent ultraviolet-PD and a very promising candidate for practical applications.
TL;DR: In this article, the authors measured electrical resistance and film mass in situ during exposure to controlled pulses of O2 and H2O vapor, and found evidence of decoupling of CuPc from the gold-coated QCM crystal.
Abstract: Copper phthalocyanine (CuPc) is an important hole transport layer for organic photovoltaics (OPVs), but interaction with ambient gas/vapor may lead to changes in its electronic properties and limit OPV device lifetimes. CuPc films of thickness 25 and 100 nm were grown by thermal sublimation at 25°C, 150°C, and 250°C in order to vary morphology. We measured electrical resistance and film mass in situ during exposure to controlled pulses of O2 and H2O vapor. CuPc films deposited at 250°C showed a factor of 5 higher uptake of O2 as detected by a quartz crystal microbalance (QCM), possibly due to the formation of β-CuPc at T>200°C which allows higher O2 mobility between stacked molecules. While weight-based measurements stabilize after ∼10 min of gas exposure, resistance response stabilizes over times >1 h, suggesting that mass change occurs by rapid adsorption at active surface sites whereas resistive response is dominated by slow diffusion of adsorbates into the bulk film. The 25 nm films exhibit higher resistive response than 100 nm films after an hour of O2/H2O exposure due to fast analyte diffusion down to the film/electrode interface. We found evidence of decoupling of CuPc from the gold-coated QCM crystal due to preferential adsorption of O2/H2O molecules on gold.
TL;DR: In this article, a 22×25 mm 2 cell that contained 0.5 wt. % coumarin 6 in a nematic liquid crystal (LC) host was fabricated and the alignment was antiparallel and the gap was 6
Abstract: One can convert a luminescent solar concentrator to a display by scanning a laser beam on it. When a guest–host system of liquid crystal (LC) and dye materials are incorporated, absorption of excitation light and the radiation pattern of photoluminescence (PL) can be adjusted to changes in lighting condition. The resolution of a displayed image can be degraded by PL spreading in the LC/dye layer. Its contrast can be limited by the PL induced by ambient light. In the experiment, we fabricated a 22×25 mm 2 cell that contained 0.5 wt. % coumarin 6 in a nematic LC host. The alignment was antiparallel and the gap was 6 μ m . Using a blue laser beam of 0.04 mm FWHM, the PL intensity distribution was measured to be 0.20 mm FWHM at zero bias. It became slightly wider at 10 V. For contrast evaluation, we measured PL spectra under two conditions. First, the center of the cell was irradiated by a 1.7-mW blue laser beam. Second, the whole cell was uniformly exposed to light from a fluorescent lamp at illuminance of 800lx. The contrast of luminance was calculated to be 1.4×10 5 . The optical power reaching its edge surfaces was measured and roughly agreed with the prediction by a simple model.
TL;DR: In this article, the degradation dynamics of organic solar cells (OSCs) taking into account the light-soaking effect was investigated for 100 days and a measurement procedure for proper investigation of light soaking effect was proposed.
Abstract: One of the issues in the organic solar-cell technology that needs attention before mass production is its low long-term stability. These devices need often to be exposed to the light to improve their photovoltaic properties. This effect, known as light soaking, is the cause of challenges related to correct measurements and proper determination of the device lifetime. Lifetime determination and investigation of failure mechanisms of solar-cell devices require reliable measurement approaches. This paper presents the systematic studies on proper analysis of degradation dynamics of organic solar cells (OSCs) taking into account the light-soaking effect. Five groups of organic solar-cell annealed at various conditions (110°C to 170°C and nonannealed) were under investigation for 100 days. Measurement procedure for proper investigation of light-soaking effect is proposed. Solar-cell efficiency improvement, due to light-soaking effect, in range 8% to 27% was observed for as fabricated devices. After 100 days of study, the light soaking-related efficiency improvement increased up to over 100% of initial efficiency. Device lifetimes strongly depend on measurement methods, which were applied. Our results show the importance of taking into account the changes in magnitude of the light-soaking effect in measurements and degradation studies of OSCs.
TL;DR: In this paper, a conformal TCO/semiconductor/metal nanowire (NW) array was proposed for hot-electron photodetection with a tunable optical response across the visible and near-infrared bands.
Abstract: The use of hot electrons arising from the nonradiative decay of surface plasmons (SPs) is increasingly attracting interests in photodetection, photovoltaics, photocatalysis, and surface imaging. Nevertheless, the quantum efficiency of the hot-electron devices has to be improved to promote the practical applications. We propose an architecture of conformal TCO/semiconductor/metal nanowire (NW) array for hot-electron photodetection with a tunable optical response across the visible and near-infrared bands. The wavelength, strength, and bandwidth of the plasmonic resonance are tailored by controlling the lattice periodicity and topology. Finite-element simulation demonstrates that the near-perfect, polarization-insensitive, and ultranarrow-band optical absorption can be achieved in the conformal NW system. By the excitation of localized SPs, a strong field concentrates at the top corner of the NWs with a high hot-electrons generation rate. The analytical probability-based electrical calculation further shows that the SPs-enhanced photoresponsivity can be more than five times larger than that of the flat reference.