Photoenergy Conversion Efficiency Research Articles

Novel water/oxygen cycle reaction photo fuel cell for solar conversion and pollutant detection: Based on selective 2-electron collaborative catalysis process

New typed photovoltaic devices, represented by water/oxygen cycle based photo fuel cells (PFCs) as a promising strategy to resolve the fossil energy crisis, have attracted extensive attention for the ideal photo energy conversion and utilization efficiency, spontaneous operation, and miniaturized devices. However, they still have limitations such as low oxygen reduction efficiency and poor stability caused by the complex structure of the cathode. In this work, a synergetic and fast 2-electron water/oxygen cycle reaction based dual-photoelectrode fuel cell (DPFC) is constructed with molecularly imprinted (MI)-CdS/ZnO nanorods (NRs) as photoanode and p-type organic semiconductor polythiophene (pTTh) as photocathode for the first time. The larger self-bias and simple structure endow the device higher open circuit potential (EOCV = 1.07 ± 0.08 V) and ideal output power density (Pmax = 60.5 ± 2.1 μW·cm−2). Attributed to the synergistic reaction effects, the 2-electron water/oxygen cycle is realized by the photocathode-generated H2O2 to serve as shuttle molecule, with outstanding cyclic stability (96 %) in 64 h continuous irradiation. Moreover, a portable self-powered sensor for the typical environmental pollutant atrazine is successfully developed based on this DPFC. A very wide concentration range (0.002 to 50 nM) and a super low detection limit (0.19 pM) is achived via a digital multimeter without the assistance of any signal amplifier. The mechanism, pathway, and active site of the selective reduction process are studied by the attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). This work has proposed a cheap and regulatable new way to convert and utilize solar energy and provided theoretical guidance for achieving economic power generation and the sensing strategy of self-powered sensors.

Enhanced Charge Separation and Transfer Efficiency of BiOI with the Dominantly Exposed (102) Facet for Sensitive Photoelectrochemical Photodetection.

Bismuth oxyiodide (BiOI) has attracted much attention as a kind of novel functional material because of its highly anisotropic crystal structure and promising optical properties. However, the low photoenergy conversion efficiency of BiOI highly limits its practical applications owing to its poor charge transport. Tailoring the crystallographic orientation has emerged as an effective way to modulate the charge transport efficiency, while there is nearly no report on BiOI. In this study, (001)- and (102)-oriented BiOI thin films were synthesized for the first time with mist chemical vapor deposition at atmospheric pressure. The photoelectrochemical response for the (102)-oriented BiOI thin film was much better than that of the (001)-oriented thin film, owing to the enhanced charge separation and transfer efficiency. The intensive surface band bending and larger donor density for (102)-oriented BiOI were the main origins of the efficient charge transport. Besides, the BiOI-based photoelectrochemical-type photodetector exhibited excellent photodetection performance with a high responsivity of 78.33 mA W-1 and a detectivity of 4.61 × 1011 Jones for visible light. This work provided fundamental insights into anisotropic electrical and optical properties in BiOI, which would be beneficial for the design of bismuth mixed-anion compound-based photoelectrochemical devices.

Synthesis and experimental investigations of organic perovskite solar cell material; 2,5-bis(5-aminofuran-2-yl) thiophene 1,1-dioxide; photo-voltaic data validation using computational model and spectroscopic tools

The Doped crystal architectures based on the Perovskite structure are most promising for creating photovoltaic solar cells. In recent years, much research effort has been directed towards increasing the solar power conversion efficiency of organic crystal materials. The ultimate challenge is to improve the light-harvesting power gain in organic synthetic materials and it was proved from the attainment of the Birefringence (Δn) Kλ/t −1.98. In this context, we report herein fabrication of organic 2,5-bis(5-aminofuran-2-yl) thiophene 1,1-dioxide as a perovskite-like lattice in the form of molecular clusters. Its photo-conversion efficiency was calculated as 18%. Its short-circuit current density was determined as JSC = 0.91 mA/cm2, with open-circuit voltage VOC of 1.05 V. The charge transfer (CT) exciton binding energy variation of dielectric constant of the material medium has been calculated. The diffusion path length was defined as <10 Å and the direct band gap was measured as 2.15 eV. The Urbach energy of the prepared sample was estimated as 110–220 meV. The molecular mechanism of exciton productions in the photo-voltaic process has been probed through the use of computational software and experimental tools. The light harvesting ability has been assessed in terms of morphological, optical and electro-optical properties. To characterize weak interactions between the organic molecular sites, vibrational studies have been carried out on polar and nonpolar bonds. The production of Frenkel excitons at the HOMO-LUMO interface and the binding energy variation for electron-hole dissociation has been estimated from the Coulomb capture radius. The photo-energy conversion efficiency and fill factor (FF = 0.511) have been estimated to prove the efficiency of the cell.

Role of Pi-Electron Density at the Interface of Small Molecule-Sensitized Solar Cells

Conventional dye-sensitized solar cells (DSSCs) involving charge-transfer interfaces face charge injection losses and offsets for TiO2-sensitizer band alignment. The direct charge-transfer mechanism in DSSCs with catechol (CT, 1,2-benzenediol)-based compounds minimizes the injection losses and eliminates band alignment issues, although the photovoltaic performance of the corresponding device is very poor due to the ultrafast (picosecond) recombination of photoexcited electrons. Just as in a natural photosystem, structural selectivity toward inhibition of this recombination needs to be defined. The interfacial electron density and back electron transfer kinetics at the molecular sensitizer–TiO2 interface play a significant role in the overall energy conversion efficiency. Herein, we identified, for the first time, that the π-electron cloud at the sensitizer–TiO2 interface facilitates the degree of recombination. Comparative density functional theory analyses confirmed that these electron clouds act as large recombination sites. Luminol (LM) and isoluminol (ILM) were employed as “small molecule” sensitizers without the cloud, having a secondary amine linker, which increased the photoenergy conversion efficiency of the single-step sensitization-based photovoltaic cell (type-II DSSC) by reducing the recombination. The device with LM exhibited a power-conversion efficiency (PCE) of ca. 1.11% (representing 363% improvement when compared to CT), the highest ever reported in this category. This understanding is insightful for the design of novel small molecular sensitizers for future DSSCs.

Photoinduced Rechargeable Lithium-Ion Battery.

Lithium-ion battery (LIB) design is the predominant technology to power portable and mobile electric devices/equipment. Fast charging and self-powering of LIBs are significant but challenging features to be addressed for meeting the fast-paced society and emerging demands. Herein, we report a rational photorechargeable lithium-ion battery (photo-LIB) design using LiV2O5 as a photocathode by directly modifying a commercial LIB without using any additives, which works in both photoassisted fast charging and photo-only charging modes. The photo-LIB attains a high specific capacity of 185 mAh g-1 in as fast as 5 min under illumination, an enhancement of 270% referring to that in dark. Under the photo-only charging mode, the device achieves a highest full-spectrum photo-energy conversion efficiency of 9% so far, demonstrating a highly efficient self-powering mode. We reveal that the improved performance of photo-LIB is due to reversible vanadium intervalence charge transfer and Li+ insertion/deinsertion in LiV2O5 under illumination.

Analysis of the characteristics of paulownia lignocellulose and hydrogen production potential via photo fermentation

Paulownia biomass is rich in carbohydrates, making which a potential feedstock for biohydrogen production. In the study, different parts and varieties of Paulownia were chose as substrates to evaluate hydrogen production potential of paulownia lignocellulose via biohydrogen production by photo fermentation (BHPPF) and energy conversion efficiency (ECE). Results showed the highest cumulative hydrogen yield (CHY) of 67.11 mL/g total solids (TS) and ECE of 4.74% were obtained from leaves of Paulownia, which were 121.06% and 115.45% higher than those of the branches. Moreover, Paulownia jianshiensis leaves were found to be the best variety for BHPPF, with the maximum CHY of 98.83 mL/g TS and ECE of 7.18%. Using Paulownia waste as the substrate to produce hydrogen helps broaden the range of raw materials for BHPPF and improve the economic utilization of forestry waste.

Polyaniline/Ag2S–CdS Nanocomposites as Efficient Electrocatalysts for Triiodide Reduction in Dye-Sensitized Solar Cells

In this study, an Ag2S–CdS nanocomposite (AC11) was prepared through chemical co-precipitation of silver nitrate and cadmium acetate in an aqueous solution of thiourea. We then synthesized PACI, a nanocomposite of polyaniline (PANI) and AC11, through in situ polymerization of aniline in an AC11-containing solution, resulting in uniform embedding of the AC11 nanoparticles in the PANI fibers. Moreover, we synthesized the nanocomposite PACO through deposition of the AC11 nanoparticles on the surface of the PANI fibers. PANI, PACI, and PACO were then spin-coated onto conducting glasses to form PANI-S, PACI-S, and PACO-S counter electrodes, respectively, for dye-sensitized solar cells (DSSCs). Cyclic voltammetry revealed that the electrochemical catalytic activity of the PACI-S electrode was much higher than those of the PANI-S and PACO-S electrodes. Furthermore, the photovoltaic properties of the PACI-S-based DSSC were much better than those of the PANI-S- and PACO-S-based DSSCs. Indeed, the highest short-circuit current density (12.06 mA/cm2), open-circuit voltage (0.72 V), fill factor (0.58), and photoenergy conversion efficiency (5.04%) were those of the DSSC featuring PACI-S as the counter electrode.

Fabrication of Zn3(PO4)2/carbon nanotubes nanocomposite thin film via sol-gel drop coating method with enhanced photocatalytic activity

Thin films of Zn3(PO4)2 and Zn3(PO4)2/carbon nanotubes (Zn3(PO4)2/CNT) were fabricated on glass substrate by the simple sol-gel drop coating method. The crystal structure, particle size, morphology and optical properties were characterized by X-ray Diffraction, Field Emission Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy (FT-IR) and Ultraviolet-visible Spectroscopy. The X-ray diffraction results revealed the formation of zinc phosphate crystal without any impurities as well as the average particle size of 24 nm and 19 nm for Zn3(PO4)2 and Zn3(PO4)2/CNT, respectively. FT-IR spectral data confirmed the grafting of the polar carboxylic and hydroxyl functional groups on the surface of nanotubes due to functionalization and also the presence of PO43- group. The formation of heterojunction interface between CNT and Zn3(PO4)2 reduce the fast recombination of charge carriers, which leads to the high photoenergy conversion efficiency. The as-synthesized Zn3(PO4)2/CNT composite thin film showed highest photocatalytic efficiency for the degradation of cationic organic dye methylene blue under ultraviolet (UV) (85%) and visible (53%) light irradiation. Incorporation of CNT with the Zn3(PO4)2 enhanced the photocatalytic efficiency two fold in case of UV and four fold higher in presence of visible light irradiation as high as bare Zn3(PO4)2. We offer that this work will smooth the progress of preparation of innovative phosphate based photocatalysts for degradation of organic pollutants from environment under UV light illumination. Furthermore, a plausible photocatalytic degradation mechanism of an organic pollutant by the synthesized Zn3(PO4)2/CNT composite is proposed.

Stable Organic Photosensitizer Nanoparticles with Absorption Peak beyond 800 Nanometers and High Reactive Oxygen Species Yield for Multimodality Phototheranostics.

Effective multimodality phototheranostics under deep-penetration laser excitation is highly desired for tumor medicine, which is still at a deadlock due to lack of versatile photosensitizers with absorption located in the long-wavelength region. Herein, we demonstrate a stable organic photosensitizer nanoparticle based on molecular engineering of benzo[c]thiophene (BT)-based photoactivated molecules with strong wavelength-tunable absorption in the near-infrared region. Via molecular design, the absorption and singlet oxygen generation of BT molecules would be reliably tuned. Importantly, the nanoparticles with a red-shifted absorption peak of 843 nm not only show over 10-fold reactive oxygen species yield compared with indocyanine green but also demonstrate a notable photothermal effect and photoacoustic signal upon 808 nm excitation. The in vitro and in vivo experiments substantiate good multimodal anticancer efficacy and imaging performance of BT theranostics. This work provides an organic photosensitizer nanoparticle with long-wavelength excitation and high photoenergy conversion efficiency for multimodality phototherapy.

Controllable synthesis of ZnO nanorods at different temperatures for enhancement of dye-sensitized solar cell performance

Vertically-aligned ZnO nanorods were grown on fluorine-doped tin oxide (FTO) substrates at different bath temperatures. This method has been effectively applied to fabricate efficient nanorod based photo-anodes for dye-sensitized solar cells (DSSCs). Photovoltaic performance of the cell was found to be enhanced on the bath temperature used to synthesize nanorods. Crystallinity and morphology of the prepared ZnO nanorod has been studied using X-ray diffraction pattern (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectrometer (EDS), Transmission Electron Microscopy (TEM), UV–Visible spectroscopy and Current–Voltage (J–V) measurements. The effect of bath temperature on the photovoltaic performance was investigated under one-sun illumination. The photo-energy conversion efficiency (PCEs) shows that DSSCs prepared at lower bath temperature shows better performance than those prepared at higher bath temperature.

Spatial Heterojunction in Nanostructured TiO2 and Its Cascade Effect for Efficient Photocatalysis.

A highly efficient photoenergy conversion is strongly dependent on the cumulative cascade efficiency of the photogenerated carriers. Spatial heterojunctions are critical to directed charge transfer and, thus, attractive but still a challenge. Here, a spatially ternary titanium-defected TiO2@carbon quantum dots@reduced graphene oxide (denoted as VTi@CQDs@rGO) in one system is shown to demonstrate a cascade effect of charges and significant performances regarding the photocurrent, the apparent quantum yield, and photocatalysis such as H2 production from water splitting and CO2 reduction. A key aspect in the construction is the technologically irrational junction of Ti-vacancies and nanocarbons for the spatially inside-out heterojunction. The new "spatial heterojunctions" concept, characteristics, mechanism, and extension are proposed at an atomic-/nanoscale to clarify the generation of rational heterojunctions as well as the cascade electron transfer.

Pt-TCO free sn-ag-cu ternary alloy as cost effective counter electrode layer for dye sensitized solar cell

The performance of dye sensitized solar cell (DSSC) is largely dependent on efficient electron reclamation from outer circuit to reduce the oxidized redox shuttle (electrolyte). The current transparent conducting oxide (TCO) glass substrates and platinum (Pt) metal as essential components of counter electrodes though efficient are very expensive which restrict commercialization of this technology. Furthermore, the sluggish catalytic activity of indium tin oxide (ITO) or fluorine doped tin oxide (FTO) play no role in electron reclamation. In this study, commercially available cost effective tin-silver-copper (Sn-Ag-Cu) ternary composite past has been investigated as potential replacement for FTO coating and Pt catalyst to work in conjunction with counter electrode of dye sensitized solar cell. Scanning electron microscopy (SEM) has been utilized to examine the morphology of as received paste. Electrochemical analysis such as cyclic voltammetery (CV) and electron impedance spectroscopy (EIS) have been employed to investigate the catalytic activity and electron kinetics respectively. Finally, current-voltage characteristics have been investigated using IVT 2600 solar simulator. The Sn:Ag:Cu composite exhibited remarkable catalytic properties which in turn lead to impressive over all photo energy conversion efficiency. The measured conversion efficiency was 6.78% which is almost 86% equivalent to DSSCs containing Pt has catalyst on FTO.

(Invited) Novel Plasmonic Nanomaterials for Near Infrared Light Energy Conversion

The structure of nanomaterial determines their individual properties and assembled structures they can form [1,2].Highly efficient photoenergy conversion in heterostructured nanocrystals (HNCs) requires the formation of epitaxial heterointerfaces and band alignment engineering.One of the phases in HNCs should hold the light absorbing ability, such as narrow band gap semiconductor [3-6] and plasmonic material [7-9].Special attention has been given to the HNCs with the combination of plasmonic semiconductor/semiconductor [7-9], where the near infrared plasmon-induced carrier transfer takes place to realize the long-lived charge separation and near infrared light energy conversion into electricity [8] and chemical energy [7,9]. [1] Wu, H.-L.; Teranishi, T. et al. Science 2016, 351, 1306. [2] Kanehara, M.; Arakawa, H.; Honda, T.; Saruyama, M.; Teranishi, T. Chem. Eur. J. 2012, 18, 9230. [3] Saruyama, M.; So, Y.-G.; Kimoto, K.; Taguchi, S.; Kanemitsu, Y.; Teranishi, T. J. Am. Chem. Soc. 2011, 133, 17598. [4] Sakamoto, M.; Teranishi, T. et al. Chem. Sci. 2014, 5, 3831. [5] Teranishi, T.; Samamoto, M. J. Phys. Chem. Lett. 2013, 4, 2867. (Perspective) [6] Sakamoto, M.; Teranishi, T. et al. Nanoscale 2016, 8, 9517. [7] Lian, Z.; Sakamoto, M.; Teranishi, T.et al. Nat. Commun. 2018, 9, 2314. [8] Sakamoto, M.; Teranishi, T.et al. Nat. Commun., accepted. [9] Lian, Z.; Sakamoto, M.; Teranishi, T. et al. J. Am. Chem. Soc., accepted.

Effect of Nickel Oxide on the Conductivity of Polymer Blend Electrolyte Doped with Sodium Iodide and Its Application in Dye-Sensitized Solar Cell

Ionic conductivity of electrolyte is one of the factor that influences the efficiency of dye-sensitized solar cell (DSSC). Herein, gel polymer electrolyte (GPE) consist of polyacrylonitrile (PAN), poly(1-vinylpyrrolidone-co-vinyl acetate) (P(VP-co-VAc)), sodium iodide (NaI) dopant and nickel oxide (NiO) additive was prepared using solution casting method. The ionic conductivity study revealed that after the inclusion of NiO, the conductivity was increased from 2.33 mS cm-1 (for polymer blend) to 4.84 mS cm-1. Besides the dielectric properties, the electrical modulus study was conducted to analyse the effect of electrode polarization and ionic conductivity of the GPE. Under the exposure of AM 1.5, the fabricated DSSC utilizing the prepared GPE exhibited photoenergy conversion efficiency of 3.98% with a short circuit current density (JSC) of 15.03mA cm-2, open circuit voltage (VOC) of 0.57 mV and fill factor (FF) of 44.0 %.

Effect of Nickel Oxide on the Conductivity of Polymer Blend Electrolyte Doped with Sodium Iodide and Its Application in Dye-Sensitized Solar Cell

Ionic conductivity of electrolyte is one of the factor that influences the efficiency of dye-sensitized solar cell (DSSC). Herein, gel polymer electrolyte (GPE) consist of polyacrylonitrile (PAN), poly(1-vinylpyrrolidone-co-vinyl acetate) (P(VP-co-VAc)), sodium iodide (NaI) dopant and nickel oxide (NiO) additive was prepared using solution casting method. The ionic conductivity study revealed that after the inclusion of NiO, the conductivity was increased from 2.33 mS cm-1 (for polymer blend) to 4.84 mS cm-1. Besides the dielectric properties, the electrical modulus study was conducted to analyse the effect of electrode polarization and ionic conductivity of the GPE. Under the exposure of AM 1.5, the fabricated DSSC utilizing the prepared GPE exhibited photoenergy conversion efficiency of 3.98% with a short circuit current density (JSC) of 15.03mA cm-2, open circuit voltage (VOC) of 0.57 mV and fill factor (FF) of 44.0 %.

Reconstruction of Solar Fuel Ultrathin Films via Periodically Microbending for Efficient Photoelectrochemical Water Splitting

Tackling the conflict between the optical and electronic properties of the ultrathin optoelectronic films is of critical importance for the development of highly efficient photoenergy conversion devices. We show in this report a proof of concept for designing an ultrathin photoelectrode film that compensates intrinsic low absorption coefficients and limited charge-carrier transport properties. To enhance light absorption under these conditions a light trapping structure using coupled optical properties was designed on the basis of an array of hollow half spheres generated by periodically microbending the deposited thin film, yielding well-defined two-dimensional ordered microspaces. Exemplified by α-Fe2O3, this film structure is able to generate an approximately 4.5-fold increase in photocurrent at a bias of 1.23 V versus RHE under simulated solar radiation conditions compared to that of a flat film with the same thickness. Both the experimental results and the theoretical simulations prove that modulatin...

Direct Observation of Node-to-Node Communication in Zeolitic Imidazolate Frameworks.

Zeolitic imidazolate frameworks (ZIFs) with open-shell transition metal nodes represent a promising class of highly ordered light harvesting antennas for photoenergy applications. However, their charge transport properties within the framework, the key criterion to achieve efficient photoenergy conversion, are not yet explored. Herein, we report the first direct evidence of a charge transport pathway through node-to-node communication in both ground state and excited state ZIFs using the combination of paramagnetic susceptibility measurements and time-resolved optical and X-ray absorption spectroscopy. These findings provide unprecedented new insights into the photoactivity and charge transport nature of ZIF frameworks, paving the way for their novel application as light harvesting arrays in diverse photoenergy conversion devices.

The Effect of Incorporation of Multi-Walled Carbon Nanotube into Poly(Ethylene Oxide) Gel Electrolyte on the Photovoltaic Performance of Dye-Sensitized Solar Cell

ABSTRACTGel polymer electrolytes (GPEs) consist of poly(ethylene oxide) (PEO), sodium iodide (NaI) and different amount of multi-walled carbon nanotubes (MWCNT) were prepared. The conductivity study revealed that the highest ionic conductivity of GPE was 7.02 × 10−3 S cm−1. The structural and complexation between the materials are authenticated via X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Under the exposure of AM 1.5, the fabricated DSSCs exhibited the highest photoenergy conversion efficiency of 7.23% with a short circuit current density (JSC) of 18.64 mA cm−2, open circuit voltage (VOC) of 0.590 mV and fill factor (FF) of 65.7%.

Atomic-Scale Mott-Schottky Heterojunctions of Boron Nitride Monolayer and Graphene as Metal-Free Photocatalysts for Artificial Photosynthesis.

Heterojunction photocatalysts at present are still suffering from the low charge separation/transfer efficiency due to the poor charge mobility of semiconductor‐based photocatalysts. Atomic‐scale heterojunction‐type photocatalysts are regarded as a promising and effective strategy to overcome the drawbacks of traditional photocatalysts for higher photoenergy conversion efficiencies. Herein, an atomic‐scale heterojunction composed of a boron nitride monolayer and graphene (h‐BN‐C/G) is constructed to significantly shorten the charge transfer path to promote the activation of molecular oxygen for artificial photosynthesis (exemplified with oxidative coupling of amines to imines). As the thinnest heterojunction, h‐BN‐C/G gives the highest conversion, which is eightfold higher than that of the mechanical mixture of graphene and boron nitride monolayers. h‐BN‐C/G exhibits a high turnover frequency value (4.0 mmol benzylamine g−1 h−1), which is 2.5‐fold higher than that of the benchmark metal‐free photocatalyst in the literature under even critical conditions.

Visible laser-assisted reduction of plasmonic Ag nanoparticles with narrow-band optical absorption for colored holographic reconstruction.

Noble metal plasmonic resonance has been utilized in optical data storage widely for its excellent photo-transformation efficiency. TiO2 nanoporous films deposited with Ag nanoparticles present outstanding polarization-response and color-modulation ability. However, the low exposure-sensitivity at single wavelength inhibits their application in optical information processing, which is urgent to be improved by innovative methods. Here, we report that Ag nanoparticles were deposited efficiently via continuous laser irradiation in the TiO2 nanoporous film treated by tannic acid, presenting high-efficient monochromic absorption property. As a result, two sets of holograms were recorded sequentially at the same point of the film with orthogonal circular polarization configurations. The colored reconstruction of the mixed holograms was achieved by utilizing laser polarization state as chrominance segmentation channel. Our method provides a distinctive route for enhancing the photo-energy conversion efficiency of plasmonic nanoparticles, and paves a way to develop advanced display device.