VOC Measurements Research Articles

Facile Method of Solvent-Flushing To Building Component Distribution within Photoactive Layers for High-Performance Organic Solar Cells.

Suitable donor and acceptor distribution in the blended photoactive layer benefits the charge transfer and exciton separation to boost the performance of organic solar cells (OSCs). Herein, we propose a universal solvent-flushing method for building component distribution in photoactive layers based on the different solubilities of the donor and acceptor in acetylacetone (Acac). The donor and acceptor concentration distribution through the photoactive layers is investigated by the time-of-flight secondary-ion mass spectroscopy, and the surface concentration changes are examined by contact angle measurements and atomic force microscopy tests. The charge-transfer properties of OSCs before and after Acac flushing are further investigated by the rectification ratio and light intensity-dependent Jsc and Voc measurements. For inverted OSCs based on PBDB-TF:IT-4F, the power conversion efficiency (PCE) enhances from 12.87 to 14.05%, and for a PBDB-TF:Y6-based device, the PCE also significantly increases from 15.40 to 16.51% because of greatly enhanced Jsc and FF, benefited from enhanced charge transport and suppressed charge recombination by solvent-flushing. Our findings suggest that solvent-flushing is a simply processed and easily controlled method to achieve vertical component distribution in photoactive layers to boost the performance of OSCs.

RETRACTED ARTICLE: Nanostructures of chemically modified multi-walled carbon nanotubes and poly(3-hexylthiophene) to improve photophysic/photovoltaic features

Multi-walled carbon nanotube/poly(3-hexylthiophene) (CNT/P3HT) and CNT-graft-poly(3-dodecylthiophene) (PDDT)/P3HT nanohybrids were applied in active layers to study the effects of these nanostructures on the polymer solar cell (PSC) performance. The charge-carrier dynamics and photophysics were studied in the binary and ternary systems based on P3HT, pre-developed nanostructures and/or phenyl-C71-butyric acid methyl ester (PC71BM) through the electrochemical impedance spectroscopy and morphological analyses. The weaker bimolecular recombination in the photoactive layer, consisting of CNT-graft-PDDT/P3HT nanostructures, was confirmed by short-circuit current (Jsc) and open-circuit voltage (Voc) measurements as a function of light intensity. PSC composed of P3HT:PC71BM:CNT-graft-PDDT/P3HT PSC exhibited the highest PCE of 4.18% with significantly increased Jsc and Voc.

Understanding the Defect Properties of Quasi-2D Halide Perovskites for Photovoltaic Applications.

Quasi-2D halide perovskites have emerged as some of the most promising photovoltaic materials owing to their excellent stability, yet the device power conversion efficiency is far from satisfactory. Besides crystal orientation-related carrier transport, defects in absorbers also play a crucial role in device performance, which has received limited attention in the 2D perovskite field. Herein, we systematically profile the defect states in 2D perovskite film by the temperature-dependent admittance spectroscopy (AS), light intensity-dependent VOC, space-charge-limited-circuit (SCLC), and photoluminescence measurements. It is revealed that the quasi-2D perovskite films suffer from severe defects as compared to the 3D counterparts in terms of both trap energy levels and trap densities. Consequently, the level of nonradiative recombination of photogenerated carriers is much greater in the corresponding devices, wherein the monomolecular recombination is dominant. These findings substantially contribute to a deeper understanding of the nature of 2D perovskite materials, which promotes the further development of 2D perovskite solar cells.

Monitoring on-road air quality and measuring vehicle emissions with remote sensing in an urban area

Simultaneous day-time measurement (8 a.m.–5 p.m.) of on-road air quality and emissions (remote sensing) on an urban road with traffic volumes varying between approximately 400-800 vehicles per hour and an average speed of about 40 km/h has been used to compare multiple measurement techniques and assess on-road air quality. It was found that observed daytime concentration levels of CO, NOx, NO2, O3, PM10 and PM2.5 are below current WHO health based guideline values, varying from a few percent (CO) to above 60% (O3 and PM2.5) of the guideline values. NO2 to NOx ratios were about a factor of two higher than measured in a previous tunnel study, which indicates that about half of measured NO2 concentrations are due to urban background levels. Statistical analysis suggest that on-road NO2 and ozone concentrations are largely driven by atmospheric chemistry processes, and not significantly affected by variation in local traffic volume and fleet mix. A significant positive weighted correlation (r = 0.71–0.74) between remote sensing and air concentration monitoring is observed for CO in calm conditions. Speciated VOC measurements on the road show large discrepancies with current COPERT (Australia) vehicle emission factors, confirming the results from an earlier tunnel study. The weight of evidence suggests that the current (EU based) VOC speciation in COPERT Australia is likely not appropriate for the Australian on-road fleet.

5.91%-efficient Sb2Se3 solar cells with a radio-frequency magnetron-sputtered CdS buffer layer

Superstrate ITO/CdS/Sb2Se3/Au thin-film solar cells were fabricated with a CdS film produced by a radio-frequency (RF) magnetron-sputtering method as the buffer layer. The effect of the CdS layer thickness (70–120nm) on the properties of Sb2Se3 thin films and the performance of the solar cells was investigated. The optimal CdS thickness was 90nm, which led to the best power conversion efficiency of 5.91%; to the best of our knowledge, this is the highest efficiency for Sb2Se3 solar cells with a sputtered CdS buffer layer to date. X-ray diffraction and scanning electron microscope results indicated that the Sb2Se3 films grown on 90-nm-thick CdS layers had the optimal grain orientation and the best morphology. The current–voltage (J–V) and admittance results indicated that the Sb2Se3 cell with a 90-nm-thick CdS layer had the lowest saturation current and the smallest defect densities. Moreover, temperature- and light intensity-dependent open-circuit (Voc) measurements revealed that the carrier recombination rates at the CdS/Sb2Se3 interface, space-charge region (SCR), and quasi-neutral region (QNR) all achieved the smallest value for the Sb2Se3 cells with a 90-nm CdS buffer layer. These data account for the optimal cell performance and offer new research directions for solving challenges of chemical bath deposition of CdS in Sb2Se3 solar cells.

Investigation of electronic transport mechanisms in Sb2Se3 thin-film solar cells

Electronic transport mechanisms in Sb2Se3 thin-film solar cells were investigated using temperature-dependent current-voltage (J-V) measurements. Sb2Se3 thin films were deposited via the vapor transporting deposition method using a double-temperature-zone tubular furnace system, and comparative studies were performed for Sb2Se3 films formed on substrates located at three different positions away from the furnace center. The device efficiency varied from 3.83 to 6.24%. First, structural properties obtained by X-ray diffraction, Raman and scanning electron microscopy measurements verified the optimal Sb2Se3 film quality for the cell with the highest efficiency. Then, temperature-dependent saturation current and open-circuit voltage (Voc) measurements revealed that the dominant carrier recombination occurred in the CdS/Sb2Se3 interface region, which possibly influenced the Voc for all cells: the highest Voc for the optimal Sb2Se3 cell was at least partly due to it having the lowest CdS/Sb2Se3 interface recombination rate. Finally, the reverse bias current relationship revealed that non-ohmic shunt current (space-charge-limited current, SCLC) plays an important role in affecting the performance of solar cells, as lower-efficiency cells had higher non-ohmic shunt current.

Transient analysis of luminescent coupling effects in multi-junction solar cells

We investigate the luminescent coupling (LC) effects in a four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cell based on transient open-circuit voltage (Voc) measurements under monochromatic illumination. Photocurrent generation in the non-absorbing GaInAs bottom subcell due to LC from upper subcells shows superlinear behavior with increasing light intensity. Along with this, a Voc enhancement is observed and quantified for illumination intensities that span almost six orders of magnitude. The Voc increase is explained and studied using a series-connected diode model including subcell shunt resistances, capacitances, and LC effects. The impact of unilluminated subcells on the subcell Voc determination is discussed for multi-junction solar cells. Finally, in the analysis of the LC generated photocurrent, namely, the coupling factor from the GaInAsP to the non-absorbing GaInAs subcell, a characteristic dependency on bias voltage is shown and explained by a result of competing photo- and electroluminescence mechanisms.

Driving parameters of biogenic volatile organic compounds and consequences on new particle formation observed at an eastern Mediterranean background site

Abstract. As a part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) and Cyprus Aerosols and Gas Precursors (ENVI-Med CyAr) programs, this study aims primarily to provide an improved understanding of the sources and the fate of volatile organic compounds (VOCs) in the eastern Mediterranean. More than 60 VOCs, including biogenic species (isoprene and eight monoterpenes) and oxygenated VOCs, were measured during a 1-month intensive field campaign performed in March 2015 at the Cyprus Atmospheric Observatory (CAO), a regional background site in Cyprus. VOC measurements were conducted using complementary online and offline techniques. Biogenic VOCs (BVOCs) were principally imputed to local sources and characterized by compound-specific daily cycles such as diurnal maximum for isoprene and nocturnal maximum for α- and β-pinenes, in connection with the variability of emission sources. The simultaneous study of pinene and isoprene temporal evolution and meteorological parameters has shown that BVOC emissions were mainly controlled by ambient temperature, precipitation and relative humidity. It was found that isoprene daytime emissions at CAO depended on temperature and solar radiation changes, whereas nocturnal BVOC concentrations (e.g., from oak and pine forests) were more prone to the relative humidity and temperature changes. Significant changes in monoterpene mixing ratios occurred during and after rainfall. The second part of the study focused on new particle formation (NPF) events at CAO. BVOCs are known to potentially play a role in the growth as well as in the early stages of formation of new atmospheric particles. Based on observations of the particle size distribution performed with a differential mobility particle sizer (DMPS) and the total number concentrations of particles larger than 1 nm diameter measured by particle size magnifier (PSM), NPF events were found on 14 out of 20 days of the field campaign. For all possible proxy parameters (meteorological parameters, calculated H2SO4 and measured gaseous compounds) having a role in NPF, we present daily variations of different classes during nucleation event and non-event days. NPF can occur at various condensational sink (CS) values and both under polluted and clean atmospheric conditions. High H2SO4 concentrations coupled with high BVOC concentrations seemed to be one of the most favorable conditions to observe NPF at CAO in March 2015. NPF event days were characterized by either (1) a predominant anthropogenic influence (high concentrations of anthropogenic source tracers observed), (2) a predominant biogenic influence (high BVOC concentrations coupled with low anthropogenic tracer concentrations), (3) a mixed influence (high BVOC concentrations coupled with high anthropogenic tracer concentrations) and (4) a marine influence (both low BVOC and anthropogenic tracer concentrations). More pronounced NPF events were identified during mixed anthropogenic–biogenic conditions compared to the pure anthropogenic or biogenic ones, for the same levels of precursors. Analysis of a specific NPF period of the mixed influence type highlighted that BVOC interactions with anthropogenic compounds enhanced nucleation formation and growth of newly formed particles. During this period, the nucleation-mode particles may be formed by the combination of high H2SO4 and isoprene amounts, under favorable meteorological conditions (high temperature and solar radiation and low relative humidity) along with low CS. During the daytime, growth of the newly formed particles, not only sulfate but also oxygen-like organic aerosol (OOA) mass contributions, increased in the particle phase. High BVOC concentrations were observed during the night following NPF events, accompanied by an increase in CS and in semi-volatile OOA contributions, suggesting further BVOC contribution to aerosol nighttime growth by condensing onto pre-existing aerosols.

Emission Factors of Microbial Volatile Organic Compounds from Environmental Bacteria and Fungi.

Knowledge of the factors controlling the diverse chemical emissions of common environmental bacteria and fungi is crucial because they are important signal molecules for these microbes that also could influence humans. We show here not only a high diversity of mVOCs but that their abundance can differ greatly in different environmental contexts. Microbial volatiles exhibit dynamic changes across microbial growth phases, resulting in variance of composition and emission rate of species-specific and generic mVOCs. In vitro experiments documented emissions of a wide range of mVOCs (>400 different chemicals) at high time resolution from diverse microbial species grown under different controlled conditions on nutrient media, or residential structural materials ( N = 54, Ncontrol = 23). Emissions of mVOCs varied not only between microbial taxa at a given condition but also as a function of life stage and substrate type. We quantify emission factors for total and specific mVOCs normalized for respiration rates to account for the microbial activity during their stationary phase. Our VOC measurements of different microbial taxa indicate that a variety of factors beyond temperature and water activity, such as substrate type, microbial symbiosis, growth phase, and lifecycle affect the magnitude and composition of mVOC emission.

A modeling enterprise for chemistry of indoor environments (CIE).

A modeling enterprise for chemistry of indoor environments (CIE).

Particle and Gas Emission Characterization from Oil and Oil-Dispersant Contaminated Sea Waters due to Breaking Waves

Crude oil spill incidents occur frequently, leaving seawater bodies with a verity of occupational, ecological and environmental issues from the local to global scale. Application of sub-surface dispersants to the oil contaminated water in order to break up the oil into smaller droplets has been gaining popularity in recent years as an intervention strategy. However, the use of dispersants may also have impacts on the generation and size distribution of aerosolized droplets, as well as changes in emitted gases when subjected to natural processes such as rains, winds and waves. In this study, systematic real-time measurements of total VOC (TVOC), particle-bound polycyclic aromatic hydrocarbons (PAH), and aerosol size distribution from 10 nm to 20 μm were conducted over a wave tank containing seawater, seawater plus crude oil, or seawater plus crude oil and dispersant. All experiments were performed using a wave tank (L = 6 m, W = 0.3 m and D = 0.6 m) and sensitivity analyses were conducted on key parameters including wave type, wave frequency and concentration of the added contaminants. Using gas chromatography/mass spectrometry analysis, major VOC and PAH emitting gases were determined to be hexane, cyclohexane, heptane, toluene, benzene and xylene, several of which are known carcinogens. Length of wave stroke was found to be the most influential parameter in increasing the number concentration of nano-sized particles, with the majority of the aerosolized particles smaller than 15 nm. An average of 10 times increase in TVOC concentration in the air above the water surface was observed after contaminating the sea water by 3.5 mL oil-dispersant mixture (dispersant to oil ratio of 1:25) compared to seawater alone. Wave creation led to 40 times increase in TVOC concentration (~400 times higher than the non-contaminated calm sea water). A micro-bubble generating set-up was used to evaluate whether bubble bursting was the generation mechanism of these nano-sized aerosols. Findings from this study will help to assess the risk of exposure to particulate and gases emissions from oil spills both occupationally (e.g., clean-up workers) and environmentally (e.g., people in nearby residential areas).

Ultra-Trace Real Time VOC Measurements by SIFT-MS for VIAQ

Ultra-Trace Real Time VOC Measurements by SIFT-MS for VIAQ

Source apportionment of PM2.5 size distribution and composition data from multiple stationary sites using a mobile platform

Several source apportionment studies considering multiple sites showed spatial variability of source contributions. However, setting up multiple fixed sites to collect comprehensive chemical speciation data is resource demanding. In this study, field campaigns were conducted at multiple receptor sites in the Mailiao and Taishi townships in Yunlin County using a mobile platform to demonstrate the feasibility of receptor modeling with particle size distribution and PM2.5 speciation data. Sources of air pollutants to all of the monitoring sites were identified and quantified using a modified positive matrix factorization (PMF) model. Modeling results indicated that a mixed source dominated by secondary aerosol was the largest contributor to PM2.5 at most sites. Adding VOC measurements with high time resolution helped to improve the source separation. Different patterns of source contributions among sites and seasons were observed showing both spatial heterogeneity and seasonal variation.

Photocarrier radiometry for predicting the degradation of electrical parameters of monocrystalline silicon (c-Si) solar cell irradiated by 100 KeV proton beams

In this study, the monocrystalline silicon (c-Si) solar cell irradiated by 100KeV proton beams at various fluences is investigated. A one-dimensional two-layer carrier density wave model has been developed to estimate the minority carrier lifetime of n-region and p-region of the non-irradiated c-Si solar cell by best fitting with the experimental photocarrier radiometry (PCR) signal (the amplitude and the phase). Furthermore, the lifetime is used to determine the initial defect density of the quasi-neutral region (QNR) of the solar cell to predict its I–V characteristics. The theoretically predicted short-circuit current density (Jsc), and open-circuit voltage (Voc) of the non-irradiated samples are in good agreement with experiment. Then a three-region defect distribution model for the c-Si solar cell irradiated by proton beams is carried out to describe the defect density distribution according to Monte Carlo simulation results and the initial defect density of the non-irradiated sample. Finally, we find that the electrical measurements of Jsc and Voc of the solar cells irradiated at different fluences using 100KeV proton beams are consistent with the PCR predicting results.

N-InAs based photo-thermo-electrochemical cells for conversion of solar to electrical energy

This paper presents the photo-thermo-electrochemical (PEC) response of various combinations of the n-type indium arsenide (n-InAs) photo-electrode with different counter electrodes, i.e., Ag, Al, Cu, Pb, Zn and ITO. The electrical parameters such as open circuit voltages (Voc) and short circuit current (Isc) and power output of the n-InAs/orange dye (OD)/X cells have been investigated under illumination. 5wt.% aqueous solution of OD has been used as an electrolyte. Voc and Isc measurements of the cells have been found with different emergent patterns depending upon the employed electrodes. Maximum power output has been found to be 710μW/cm2 in the case of n-InAs/OD/Al cell. The Isc is prominent in n-InAs/OD/Ag in comparison to the rest of the combinations whereas the highest value of Voc has been found in n-InAs/OD/Zn cell.

Evaluation of improved land use and canopy representation in BEIS v3.61 with biogenic VOC measurements in California

Abstract. Biogenic volatile organic compounds (BVOC) participate in reactions that can lead to secondarily formed ozone and particulate matter (PM) impacting air quality and climate. BVOC emissions are important inputs to chemical transport models applied on local to global scales but considerable uncertainty remains in the representation of canopy parameterizations and emission algorithms from different vegetation species. The Biogenic Emission Inventory System (BEIS) has been used to support both scientific and regulatory model assessments for ozone and PM. Here we describe a new version of BEIS which includes updated input vegetation data and canopy model formulation for estimating leaf temperature and vegetation data on estimated BVOC. The Biogenic Emission Landuse Database (BELD) was revised to incorporate land use data from the Moderate Resolution Imaging Spectroradiometer (MODIS) land product and 2006 National Land Cover Database (NLCD) land coverage. Vegetation species data are based on the US Forest Service (USFS) Forest Inventory and Analysis (FIA) version 5.1 for 2002–2013 and US Department of Agriculture (USDA) 2007 census of agriculture data. This update results in generally higher BVOC emissions throughout California compared with the previous version of BEIS. Baseline and updated BVOC emission estimates are used in Community Multiscale Air Quality (CMAQ) Model simulations with 4 km grid resolution and evaluated with measurements of isoprene and monoterpenes taken during multiple field campaigns in northern California. The updated canopy model coupled with improved land use and vegetation representation resulted in better agreement between CMAQ isoprene and monoterpene estimates compared with these observations.

On the origin of pronounced O3 gradients in the thunderstorm outflow region during DC3

AbstractUnique in situ measurements of CO, O3, SO2, CH4, NO, NOx, NOy, VOC, CN, and rBC were carried out with the German Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)‐Falcon aircraft in the central U.S. thunderstorms during the Deep Convective Clouds and Chemistry experiment in summer 2012. Fresh and aged anvil outflow (9–12 km) from supercells, mesoscale convective systems, mesoscale convective complexes, and squall lines were probed over Oklahoma, Texas, Colorado, and Kansas. For three case studies (30 May and 8 and 12 June) a combination of trace species, radar, lightning, and satellite information, as well as model results, were used to analyze and design schematics of major trace gas transport pathways within and in the vicinity of the probed thunderstorms. The impact of thunderstorms on the O3 composition in the upper troposphere/lower stratosphere (LS) region was analyzed. Overshooting cloud tops injected high amounts of biomass burning and lightning‐produced NOx emissions into the LS, in addition to low O3 mixing ratios from the lower troposphere. As a dynamical response, O3‐rich air from the LS was transported downward into the anvil and also surrounded the outflow. The ΔO3/ΔCO ratio was determined in the anvil outflow region. A pronounced in‐mixing of O3‐rich stratospheric air masses was observed in the outflow indicated by highly positive or even negative ΔO3/ΔCO ratios (+1.4 down to −3.9). Photochemical O3 production (ΔO3/ΔCO = +0.1) was found to be minor in the recently lofted pollution plumes. O3 mixing ratios within the aged anvil outflow were mainly enhanced due to dynamical processes.

Pemanfaatan Zat Warna Alam Kayu Jambal (Pelthophorumferugineum) sebagai Sensitizer pada Sel Surya Fotoelektrokimia

Abstract– The Natural dye of Jambal wood (Pelthophorumferugineum) was used as sensitizer in the fabrication of dye sensitizer solar cell (DSSC). The dye was extracted by using solid-liquid extraction method with ethanol as a solvent. UV-Vis spectrophotometer was used to measure the absorbance of dye solution. TiO2 thin-layer was prepared by slip coating method which the pH 5 suspension of TiO2 Degussa on HCl deposited on a glass substrate Fluorine-doped Tin Oxide (FTO).Dye adsorption was done by the immersion TiO2 thin layer in the dye solution in ethanol for 24 hours after calcination, then used as the working electrode. Counter electrode was prepared by the deposition of gold on the glass substrate.The performance of solar cells sensitized of natural Jambal wood dye was investigated through the measurements of Isc (short circuit currents) and Voc (open circuit voltage on) during irradiation with sun simulated Philips Powertone lamp. The measurement results showed that the solar cell has Isc and Voc by 56 ηA/cm2 and 394 mV respectively. Keywords– Fotoelektrokimia, Dye Sensitized Solar Cell, zatwarnaalam, Jambal.

Validation and modelling of a novel diffusive sampler for determining concentrations of volatile organic compounds in air

A novel diffusive sampler that combines radial and axial diffusion has been developed that improves upon existing commercially available designs. The POcket Diffusive (POD) sampler has been validated under laboratory and field conditions for the measurements of VOCs in ambient air. Laboratory tests varied sampling conditions of temperature (−30–40 C), humidity (10–80%), wind velocity (0.1–4 m s−1), and concentration (0.5–50 μg m−3) for a number of specific VOCs. An overall uncertainty of circa 9% for the measurement of benzene is calculated for the validation tests, in compliance with the data quality objectives of the EU air quality directive 2008/50/EC. A semi-empirical diffusion model has been developed to estimate sampling rates for compounds that were not tested, and for conditions outside of tested ranges during validation. The diffusion model (and validation tests) shows a low influence of environmental conditions on the sampling rate for the POD sampler. Average reproducibility values of circa 3% are reported with overall sampling uncertainties ranging from 9% to 15%, for the whole range of tested conditions, depending on the compound. The adsorbent cartridge is compatible with existing thermal desorption systems in the market. The diffusive sampler can modify the sampling rate by changing the diffusive body within a range of different porosities. Field tests, conducted in parallel with independent quality controlled canister sampling, confirmed the ease of use and quality of VOC measurements with the POD sampler, for compounds that were, and were not, evaluated during laboratory tests.

Heavily phosphorus-doped silicon nanoparticles as intermediate layer in solar cell based on IFO/p-Si heterojunction

The goal of this work is to investigate the effect of heavily phosphorus-doped silicon nanoparticles (NP-n+)Si introduced between the p-type silicon substrate and indium fluorine oxide (IFO) thin film on the performance of the IFO/(NP-n+/pp+)Cz-Si (Czochralski silicon)/indium tin oxide (ITO) heterojunction solar cell. Nanoparticles were deposited on p-Si surface from ethanol-based colloidal suspension by ultrasonic spray coating. The IFO and ITO films were grown by ultrasonic spray pyrolysis. A reference solar cell without nanoparticles with IFO/(pp+)Cz-Si/ITO structure was also fabricated and studied. SEM, EDX, XPS, and FTIR spectroscopy, reflection and external quantum efficiency spectra, Suns–Voc measurements were used for the analysis. It was shown that the phosphorus doping level of (NP-n+) Si is of about ∼3×1020cm−3. After deposition, NPs are covered with SiOx layer which is removed by HF dip. The mean NPs size is of about ∼5.7nm. An increase in duration of NPs deposition from 7 to 19min leads to an increase in density of NPs from 5.6×1011 to 1.06×1012cm−2 and, consequently, to an increase in NPs surface coverage from 10.6% to 27.5%. IFO/(NP-n+/pp+)Cz-Si solar cell with NPs surface coverage of 27.5% have shown noticeably higher power conversion efficiency of 13.2% in comparison with 11.9% efficiency obtained for the reference cell. This result is achieved due to increased open-circuit voltage (571mV in the NPs-based solar cell against 484mV for the reference cell).