Photo Absorber Research Articles

Phase engineering of CBD grown tin sulfide films by post-sulfurization and solar cell application

We report on post-annealing effects on structures, compositions and surface morphology of chemical bath deposition (CBD) grown tin sulfide thin films. For post-annealing of as-grown tin sulfide films, we carried out three types of sulfurization at different temperatures. As grown tin sulfide films followed by sulfurization at different conditions showed modified surface morphologies and crystalline phases; SnS, Sn2S3 and SnS2 according to the sulfurization conditions. Experimental results showed that these earth-abundant thin films could be engineered to have different structural, electrical and optical properties by simple post-sulfurization process, possessing significant potentials for wide fields of applications. Moreover, we made solar cell using SnS as photo absorber, which showed ∼0.1% power conversion efficiency.

First-Principles Study of Ion Diffusions in CH3NH3PbI3 and (NH2)2CHPbI3 for Perovskite Solar Cells

Perovskite solar cells (PSCs), which photo-absorbing layer consists of organometal halide perovskites, have gotten much attention because of their rapidly increasing power conversion efficiencies (3.8% in 2009, but nowadays over 22% cell has appeared). [1, 2] Especially, lead halide perovskites such as CH3NH3PbI3 (MAPbI3) and (NH2)2CHPbI3 (FAPbI3) show remarkable properties for solar cell applications, e.g. high optical absorption coefficients and long diffusion lengths of both charge carriers. However, the current−voltage (J−V) curve of PSCs often depends on voltage sweep rates and sweep directions, [3, 4] which make the evaluation of conversion efficiency difficult. Recently, the rate-dependent J−V hysteresis, which is due to a slow process continued about seconds, was attributed to ionic diffusions in MAPbI3. [5] In this study, we calculated activation barriers of ion diffusions in tetragonal MAPbI3 and trigonal FAPbI3 by first-principles calculations. The vacancy migrations of I− anions in both perovskites show low barriers of 0.3 to 0.45 eV, which values indicate that MAPbI3 and FAPbI3 are ion conductors. Furthermore, MA+ and FA+ cations have rather low barriers c.a. 0.6 eV. The results strongly suggest that the not only anions but also molecular cations can migrate in the perovskites when a bias voltage is applied. Based on the dilute diffusion theory, we can expect that small vacancy concentrations suppress these ion conductions. In addition, we suggest that replacement of MA molecule with larger one is also able to reduce MA migrations and to prevent the degradation of PSC photo absorbers. [6] [1] A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, J. Am. Chem. Soc., 131, 6050 (2009). [2] Best Research-Cell Efficiencies, National Renewable Energy Laboratory. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg [3] A. Dualeh, T. Moehl, N. Tétreault, J. Teuscher, P. Gao, M. K. Nazeeruddin, M. Grätzel, ACS Nano, 8, 362 (2014). [4] H. J. Snaith, A. Abate, J. M. Ball, G. E. Eperon, T. Leijtens, N. K. Noel, S. D. Stranks, J. T.-W. Wang, K. Wojciechowski, W. Zhang, J. Phys. Chem. Lett., 5, 1511 (2014). [5] W. Tress, N. Marinova, T. Moehl, S. M. Zakeeruddin, M. K. Nazeeruddin, M. Grätzel, Energy Environ. Sci., 8, 995 (2015). [6] J. Haruyama, K. Sodeyama, L. Han, and Y. Tateyama, J. Am. Chem. Soc., 137, 10048 (2015).

Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells.

Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-vis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record Voc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward current transport. Exploring ways to tune the synthesis conditions to give the high crystal quality obtained under PbI2-poor condition while maintaining the favorable grain boundary characteristics obtained under PbI2-rich conditions would thus be a strategy toward more efficiency devices.

Electronic properties of surface/bulk iodine defects of CsSnBr3 perovskite

Perovskites are one of a few semiconducting materials that have been shaping the progress of the third generation photovoltaic cells. The power conversion efficiency of the perovskite solar cell has been certified as 20.1% in 2015. In this work, CsSnBr3 perovskite has been considered as an alternative material for solar cell applications because of its appropriate band gap. The study has focused on the influence of iodine impurity on the electronic properties of CsSnBr3 perovskite modeled on the (001) surface structures. The crystal structures and the electronic properties have been calculated using density functional theory (DFT) within a plane wave pseudopotential framework. The GW method has been also employed to obtain more accurate band gaps. The results show that the iodine defect improves the efficiency of photo absorbance in perovskite solar cell by lowering its energy gap. In particular, the iodine bulk defect in the SnBr2-terminated surface structure was found to exhibit the narrowest band gap. This result suggests that iodine impurity deep into the structure, e.g. iodine-dopant created from high-energy implantation, plays an important role to improve the efficiency of light absorption in CsSnBr3 perovskite.

(Invited) Pathway to Developing Highly Efficient and Durable Photelectrochemical Device

The photoelectrochemical (PEC) conversion of solar energy to chemical fuels is an attractive and feasible route to a sustainable energy infrastructure. After the first demonstration by Fujishima and Honda in 1972,[1,2] there has been significant progress with notable conversion efficiency records established using III-V semiconductor and earth abundant silicon photocatalysts.[3,4,5,6] However, the current level of efficiency and durability are not yet sufficient for widespread commercial use of this technology. One particular challenge has been exploiting the proximity of charge carrier generation to the catalytically active sites, which is one advantage offered by a PEC device over photovoltaic-driven electrolysis. [7] In this talk, we will review key aspects in realizing high efficiency and durability in conventional III-V PEC photocatalysts and focus on the interfacial properties that are integral to reliable PEC devices. Using ab-initio molecular dynamics simulations, we first show that the hydrogen bond networks at the water-InP interface exchange themselves more freely than those at water-GaP interface, which leads to more facile diffusion of hydrogen at the interface. [8] Interestingly, it was reported that Pt catalysts can activate hydrogen evolution on the surrounding SiO2 surface of Si-based Metal-Insulator-Semiconductor solar-to-hydrogen conversion devices, with the activation suggested to take place due to hydrogen diffusion (H-spillover) at the electrolyte-insulator interface.[9] We relate these results to the III-P PEC systems and discuss a possible general device design strategy that takes advantage of this phenomena. As a next step, we have investigated the electronic structure of water-semiconductor interfaces using many-body perturbation theory (GW approximation) optimized for large systems, so as to develop more comprehensive understanding of interfacial properties (structural, electronic, and chemical) relevant for the PEC device performance.[10] We discuss how this information can be used to engineer surface treatments for fine tuning the band alignment for improved PEC performance. [11] In order to bridge the knowledge obtained from atomistic ab-initio simulations and the behavior of a macroscopic PEC device, we have also been developing highly collaborative surface validation capabilities based upon the state-of-art X-ray spectroscopy.[12] We demonstrate that X-ray spectroscopy, when combined with computational spectroscopy, can provide a detailed atomistic picture of the state of chemical species in semiconductors or on semiconductor surfaces. Such information is crucial in understanding the correlation between microscopic properties of device component materials and the device performance. Lastly, we will discuss an effective design strategy of PEC device component materials, where we leverage a tightly coupled collaboration of theory, synthesis, and characterization. The case study has been performed based on a development of thin film Cu(In,Ga)(S,Se)2 photo absorbers and the suitable buffer.[13] [1] A. Fujishima and K. Honda, Nature 238, 37 (1972). [2] J. Ager, M. Shaner, K. Walczak, I. Sharp, S. Ardo, Energy & Env. Sci. 8, 2811 (2015). [3] O. Khaselev and J. Turner, Science 280, 425 (1998). [4] R. Rocheleau, E. Miller, and A. Misra, Energy & Fuels 12, 3 (1998). [5] R. Fan et al. App. Phys. Lett. 106, 213901 (2015). [6] M. May et al. Nat. Comm. 6, 8286 (2015). [7] A. Nakamura et al. App. Phys. Exp. 8, 107 (2015). [8] B. Wood, E. Schwegler, W.-Ih Choi, T. Ogitsu, J. Am. Chem. Soc. 135, 15774 (2013). [9] D. Esposito, I. Levin, T. Moffat, A. Talin, Nat. Mat. 12, 562 (2013). [10] T. Pham et al. in preparation. [11] B. MacLeod et al. ACS App. Mat. & Int. 7, 11346 (2015). [12] W.-Ih Choi et al. in preparation. [13] J. Varley et al. in preparation.

Controllable synthesis of α-sulfur spheres with hierarchical nanostructures for efficient visible-light-driven photocatalytic ability

Visible-light-active α-sulfur spheres with hierarchical nanostructures were fabricated by simple solution-phase synthesis with PVP as the template for enhanced photocatalytic ability. The α-sulfur hierarchical spheres with an ultrahigh specific surface area can controllable synthesized by changing the addition quantity of PVP. The obtained products are systematically studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis absorption spectroscopy (DRS), Fluorescence (FL) and Brunauer-Emmett-Teller (BET). The photocatalytic activity of the as-prepared samples is evaluated by photocatalytic degradation of Rhodamine B (RhB) aqueous solution under visible light illumination. The results indicate that the morphology, specific surface area, photo absorbance ability, the separation efficiency of photogenerated carriers and the reactant adsorption performance can be controlled by varying the addition quantity of PVP. When 200mg PVP is added, α-sulfur hierarchical spheres with uniform particle size about 1μm and ultrahigh specific surface area of 67.1m2/g is obtained, and its photocatalytic activity reaches a maximum value, which can be attributed to the combined effects of photo absorbance ability, the separation efficiency of photogenerated carriers and the reactant adsorption performance.

Effect of conditions for preparation of cyclized polyacrylonitrile sensitized TiO2 nanoparticles on visible‐light photocatalysis and photo absorbance property

Cyclized polyacrylonitrile (CPAN) sensitized titanium dioxide (TiO2) nanoparticles were prepared by dip method. Photocatalysis and photo absorbance property of TiO2/CPAN were measured. The photocatalytic activity of the nanocomposites was evaluated by decomposition of an ordinary dye Reactive Brilliant Red X‐3B in an aqueous solution under visible light irradiation. Results show that TiO2/CPAN nanocomposites with CPAN content of 0.5% have the highest photocatalytic activity. The optimum cyclized temperature is 300°C, and cyclized time is 1 h. Ultraviolet‐visible diffuse reflectance spectra indicate the photo absorbance property of TiO2/CPAN nanoparticles in the range of visible light is higher than that of TiO2 nanoparticles. Fluorescence spectra indicate that introduction of trace CPAN onto TiO2 nanoparticles can efficiently decrease the recombination probability of photo‐generated electrons and holes, so the visible light photocatalysis of TiO2/CPAN nanocomposites is significantly improved. The morphology and microstructure of TiO2 and TiO2/CPAN nanocomposites were characterized by transmission electron microscopy and X‐ray diffraction. Results show that the size of TiO2/CPAN nanocomposites is similar to that of TiO2 nanoparticles. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 32–38, 2015

Study on Layer Fabrication for 3D Structure of Photoreactive Polymer Using DLP Projector

This paper presents a research on 3D part fabrication from composition of photo initiator (Phenylbis (2,4,6-trimethylbenzoyl)), photo absorber (Sudan I) and 1, 6-Hexanediol polymer effect based on curing parameters. A DLP projector was used as energy light source which initiated the photo reactive polymer at three different light source distances with three different exposed time to evaluate photoreactive polymer solidification phenomena. The experiment results obtained shows that Sudan I composition, light intensity value and exposure time of the varied photo absorber give significant effect to layer thicknes, surface roughness and hardness value. These works also prove that photo absorber composition solution gave a different mechanical properties effect for 3D microstructure fabrication.

Improvement of the nanostructured zinc oxide/polymer based solar cell efficiency through the incorporation of N,N′-dioctyl-3,4,9,10-perylenedicarboximide nanoribbons as charge mediator

We report here the effect of inserting N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) nanoribbons in between ammonia treated zinc oxide nanorods and p-type organic polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) for nanostructured ZnO/polymer based hybrid solar cell. PTCDI-C8 nanoribbons are excellent absorber of the solar spectrum in most of the visible range and energetically fitted in between ZnO and MDMO-PPV. PTCDI-C8 nanoribbons help in providing one-dimensional channel for the dissociated charges to reach the electrodes through ZnO nanorod. PTCDI-C8 nanoribbons are used as the charge transport mediator as well as the photo absorber in the solar cell device. Significant improvement in the short-circuit current was observed and it leads to the increment in the overall efficiency of this kind of nanostructure based solar cell.

Bioinspired Catecholic Copolymers for Antifouling Surface Coatings

We report here a synthetic approach to prepare poly(methyl methacrylate)-polydopamine diblock (PMMA-PDA) and triblock (PDA-PMMA-PDA) copolymers combining mussel-inspired catecholic oxidative chemistry and atom transfer radical polymerization (ATRP). These copolymers display very good solubility in a range of organic solvents and also a broad band photo absorbance that increases with increasing PDA content in the copolymer. Spin-cast thin films of the copolymer were stable in water and showed a sharp reduction (by up to 50%) in protein adsorption compared to those of neat PMMA. Also the peak decomposition temperature of the copolymers was up to 43°C higher than neat PMMA. The enhanced solvent processability, thermal stability and low protein adsorption characteristics of this copolymer makes it attractive for variety of applications including antifouling coatings on large surfaces such as ship hulls, buoys, and wave energy converters.

Parameter Optimerization for Photo Polymerization of Microstereolithography

This paper presents a research on composition photo absorber (Sudan I) effect based on curing parameter, the Liquid Crystal Display (LCD) projector as energy light source initiated the photo reactive polymer. The polymer based material with composition of 1, 6-Hexanediol dicrylate, Phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide with varied Sudan I concentration was used to build 3D structures. The structure was fabricated with three different photo absorber concentrations 0.002%, 0.003%. and 0.006%. of Sudan I. In this experiment the photoreactive polymer solidification phenomena was evaluated.The experiment result obtained, that exposed time of the varied photo absorber was most significantly affect the surface roughness values and the solidification layer time regardless the layer thickness. This work represents that photo absorber composition solution gave a different characteristics for 3D microstructure fabrication.

Eu–N-doped TiO2 photocatalyst synthesized by micro-arc oxidation

A titanium nitride layer, produced by arc ion plating method, was synthesized to give Eu–N codoped titania catalyst by using micro-arc oxidation (MAO) in the H2SO4/Eu(NO3)3 mixture solution. The N–Eu-incorporated anodic TiO2 film exhibited significantly enhanced photocatalytic activity for dye degradation, which was ascribed to the synergistic effects of the high photo absorbance response and the new electronic state of the TiO2 band gap induced by the N and Eu codoping.

Evaluation on the Photoabsorber Composition Effect in Projection Microstereolithography

This paper presents a research progress on composition photoabsorber effect the solidification time and layer thickness of 3D structures fabrication using Liquid Crystal Display (LCD) projector as energy light source to initiate the photoreactive polymer. The polymer based material with composition of 1,6-Hexanediol dicrylate, Phenylbis(2,4,6-trimethylbenzoyl)- phosphine oxide with varied Sudan I concentrations was used to build 3D structures. The structure was fabricated using a three different photo absorber composition of Sudan I then the photoreactive polymer solidification phe¬nomena was evaluated. Based on the result obtained, higher exposed time of the photo absorber will reduced the surface roughness values and increased the solidification layer time. This work represents that photo absorber composition solution gave a different characteristics for 3D microstructure fabrication.

Crystalline Characterization and Photodecomposition Properties of Rod-Shaped Na<SUB>2</SUB>Ti<SUB>6</SUB>O<SUB>13</SUB> Powder Prepared by Molten Salt Process

To prepare one-dimensional nanostructured Na2Ti6O13 powder, the starting materials of TiO2, NaCl and Na2CO3 were mixed and then heat-treated at 1000 degrees C for 2 hrs in air under molten state of NaCl. Changes in shape and phase, photo absorbance and photocatalytic ability of TiO2 particle were observed controlling added amount of Na2CO3 under constant weight ratio of TiO2 to NaCl using SEM, X-ray diffractometer, Raman spectroscopy, and UV-Vis spectroscopy. The TiO2 particle was changed into rod-shape Na2Ti6O13 with the addition of Na2CO3, showing increase in optical energy band-gap of the powder as well as gradual decrease of the photo-decomposition ability.

Formation of Macromolecule Complex with Bacillus thuringiensis Cry1A Toxins and Chlorophyllide Binding 252-kDa Lipocalin-Like Protein Locating on Bombyx mori Midgut Membrane

P252, a 252-kDa Bombyx mori protein located on the larval midgut membrane, has been shown to bind strongly with Bacillus thuringiensis Cry1A toxins (Hossain et al. Appl Environ Microbiol 70:4604-4612, 2004). P252 was also shown to bind chlorophyllide (Chlide) to form red fluorescence-emitting complex Bm252RFP with significant antimicrobial activity (Pandian et al. Appl Environ Microbiol 74:1324-1331, 2008). In this article, we show that Cry1A toxin bound with Bm252RFP and Bm252RFP-Cry1A macrocomplex, with both antimicrobial and insecticidal activities, was formed. The insecticidal activity of Bm252RFP-Cry1Ab was reduced from an LD₅₀ of 1.62 to 5.05 μg, but Bm252RFP-Cry1Aa and Bm252RFP-Cry1Ac did not show such reduction. On the other hand, the antimicrobial activity of Bm252RFP-Cry1Ab was shown to retain almost the same activity as Bm252RFP, while the other two complexes lost around 30% activity. The intensity of photo absorbance and fluorescence emission of Bm252RFP-Cry1Ab were significantly reduced compared to those of the other two complexes. Circular dichroism showed that the contents of Cry1Ab α-helix was significantly decreased in Bm252RFP-Cry1Ab but not in the other two toxins. These data suggested that the reduction of contents of α-helix in Cry1Ab affected the insecticidal activity of the macrocomplex but did not alter the antimicrobial moiety in the macrocomplex of Bm252RFP-Cry1Ab.

Preparation and Characterization of Fe-Doped BiVO<sub>4</sub>

Monoclinic crystal bismuth vanadate (BiVO4) was synthesized by the high temperature solid state reaction after ball milling the materials of Bi2O3 and V2O5. The influences of sintering times on the crystal phases and structures of BiVO4 powders were studied through the XRD、FTIR characterization. Fe-doped BiVO4 was prepared by doping ferric chloride to pure monoclinic crystal BiVO4 to improve the photo absorbance performance of BiVO4 and to promote the isolation of photo-induced carriers. Visible light activity of BiVO4 and Fe-doping BiVO4 were characterized using the UV-diffuse reflectance spectroscopy. The electrochemical behaviors of BiVO4 and Fe-doping BiVO4 were investigated under the condition of avoiding light or under light.

Radioactive Carbon Isotope Monitoring System Based on Cavity Ring-down Laser Spectroscopy for Decommissioning Process of Nuclear Facilities

In decommissioning process of nuclear facilities, large amount of radioactive isotopes are discharged as waste. Radioactive carbon isotope (14C) is one of the key nuclides to determine the upper limit of concentration in the waste disposal. In particular, 14C on the graphite reactor decommissioning should be separated from stable carbon isotopes (12C and 13C) and monitored for the public health and safety. We propose an isotope analysis system based on cavity ring-down laser spectroscopy (CRDS) to monitor the carbon isotopes (12C, 13C and 14C) in the isotope separation process for the graphite reactor decommissioning. This system is compact and suitable for a continuous monitoring, because the concentration of molecules including the carbon isotope is derived from its photo absorbance with ultra high sensitive laser absorption spectroscopy. Here are presented the necessary conditions of CRDS system for 14C isotope analysis through the preliminary experimental results of 13C isotope analysis with a prototype system.

Rapid-Swept CW Cavity Ring-down Laser Spectroscopy for Carbon Isotope Analysis

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (12C16O2, 13C16O2) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm−1(1.6)mm). The isotopic ratio has been obtained as (1.07±0.13)x 10−2, in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3x 10−8cm−1.

Rapid-Swept CW Cavity Ring-down Laser Spectroscopy for Carbon Isotope Analysis

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (12C16O2, 13C16O2) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm−1(1.6)mm). The isotopic ratio has been obtained as (1.07±0.13)x 10−2, in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3x 10−8cm−1.

Arsenic removal from water using advanced oxidation processes

Consumption of groundwaters containing natural arsenic at several hundred μg/l (ppb) in countries such as Bangladesh has lead to the increased occurrence of many cancers particularly those of the skin and bladder, while concerns in the USA and Australia regarding the unknown health impact of drinking water containing tens of ppb of arsenic is leading to increasingly stringent maximum contaminant levels. The anaerobic conditions of these groundwaters result in the arsenic being present in its reduced form, hence the use of an oxidant is necessary if the arsenic is to be successfully removed by precipitation or ion exchange methods. Advance oxidation methods which utilise ultraviolet light and a photo absorber have been developed and patented, in which both iron salts and sulphite can be used as the photoabsorber. The former absorber has been developed for arsenic removal in rural areas of Bangladesh and the latter for groundwaters in countries such as the USA.