Effect of high intensity light irradiance on CuInSe2 thin films

CuInSe2 has been a good candidate for photovoltaic material due to its direct band gap and high absorption coefficient. As the stability of photovoltaic are generally dependent on the aggressive environment, i.e. sun light, the CuInSe2 thin film can degrade after long exposure of high intensity light irradiance. The present study reports on the effect of high intensity light irradiance to the electrical and optical properties of thermal evaporated CuInSe2 thin films. The thin films were exposed to light intensity of 250 W/m2, 500 W/m2, 750 W/m2, 1000 W/m2 and 1500 W/m2 using halogen lamp. We noticed an increasing trend in resistivity after light exposure at all intensities due to the increase of light-induced defects in the films which act as recombination centre for electron-hole pair. Crystallinity of CuInSe2 thin films decreases with increasing intensity of light exposure as a result of light-induce defect. CuInSe2 thin films are found to have higher optical band gap compared to reported 1.01eV due to the amorphous structure of the film and relatively higher surface roughness

Sago wastes and its applications

The sago starch industry is one of the major revenue sources of the Malaysian state of Sarawak. This state is currently among the world’s leading producers of sago starch, exporting more than 40,000 tons every year to different Asian countries. This number is expected to rise since starch production and export value have been increasing 15.0%-20.0% each year. Sago palm is subjected to various processes to obtain starch from its trunk. During processing, a huge amount of residual solid wastes is generated, such as bark and hampas, and in general, is burned or washed off to nearby streams. Along with the rising sago starch demand, the sago starch industry is now facing waste management problems, which have resulted in environmental pollution and health hazards. These wastes comprise starch, hemicellulose, cellulose, and lignin; hence, can be valorized into feedstock as value-added products. To date, these wastes have been utilized in the production of many materials like adsorbents, sugars, biofuels, nanomaterials, composites, and ceramics. This review article aims to summarize the various methods by which these wastes can be utilized besides to enlighten the major interest on sago hampas and bark

Hydrogen Production by Membrane Water Splitting Technologies

Hydrogen production by membrane water splitting technologies is a sustainable method to synthesize hydrogen and provides an alternative to hydrogen production instead of conventional process of synthesizing hydrogen from steam methane reforming. A hybrid polymer electrolyte membrane electrolyzer operational at working temperature of above 80–200°C is advantageous for faster electrochemical kinetics, higher current exchange density, and more resistance to fuel impurities. Phosphoric acid (PA) doping onto polybenzimidazole (PBI) membrane shows significant improvement in proton conductivities, permeability, and thermal stability. PBI-based electrolyzer is relatively new to the hydrogen production technologies as compared to Nafion-based electrolyzer. However, the high cost of purchasing Nafion membrane and inability to execute electrolysis operational above 90°C has sparked new interest on PBI-based membrane, which is known for its good thermal stability

Determination of ethanol concentration of ethanol/water mixture solutions with open ended coaxial method

This study presents a simple and non-destructive procedure to determine ethanol concentration of ethanol/water solution at ambient temperature based on HP85070B open ended coaxial dielectric constant measurement. The motivation for this study stems from the fact that the `true' concentration of ethanol in a `labeled' container could be `spoiled' due to hygroscopic nature of ethanol, evaporation and other factors. The dielectric constant measurements of eight samples with different molar fraction were validated with modified Cole-Cole-Debye (3CC) simulations. A 5th degree polynomial calibration equation was developed based on 3CC simulations with R2 = 0.9998 and used to estimate the `true' concentration of three ethanol samples obtained from `labeled' containers kept in laboratory. The ethanol concentrations of two of the samples were found to be much lower than what was indicated on their labels, hence, assumed spoiled

Effect of under nitrogen annealing on photo-electrochemical characteristics of films deposited from authentic Cu2SnSe3 sources by thermal vacuum under argon gas condensation

This communication describes how annealing under nitrogen affects photo-electrochemical characteristics of films deposited from authentic Cu2SnSe3 sources by vacuum evaporation under argon gas (low flow rate 5 cm3/min) using substrate 300 °C. Annealing lowered the photoresponse of the deposited film, by affecting crystallite structure, morphology, composition and pores in the films. Annealing at temperatures in the range 150–350 °C improved crystallinity of the film but lead to pore formation between adjacent, which lowered photoresponse by increased resistance across the electrode/redox interface. Higher temperature (450 °C) annealing lead to SnO2 formation, as an additional phase, at the expense of Cu2SnS3 decomposition. Porosity and mixed phases with SnO2 presumably increased film internal resistance and resulted in poor charge transfer across the solid/redox couple interface. By affecting film characteristics, annealing lowered photoresponse for the deposited films

Hydrolysis of blended cotton/polyester fabric from hospital waste using subcritical water

Currently in Malaysia, most wastes are disposed into poorly managed systems with little or no pollution protection measures. Large amounts of wastes such as textiles are generated through hospitals and health care centers. However, the improper management of these abundantly generated wastes may pose an environmental pollution problems and fire hazard. Cotton textile is a potential biomass for bioethanol production. Subcritical water (Sub-CW) hydrolysis was investigated as an alternative technology for the recycling of cotton textile waste for current health care waste management. The aim of this study was to investigate the possibility of complete conversion of cotton textile waste to ethanol via Sub-CW hydrolysis and fermentation. Sub-CW was carried out to facilitate the hydrolysis of cellulose component in cotton textile (cotton 75%+polyester 25%). The study was divided into two parts; (i) To evaluate the subcritical water parameters such as temperature and time to achieve maximum yield of sugars. (ii) Fermentation of the hydrolysate obtained from Sub-CW hydrolysis to ethanol. Under Sub-CW conditions of temperature (140 °C - 350 °C), reaction time (1-10 min) and water to cotton ratio (3:1) showed that cotton textile treated at 280 °C for 4 min, was optimal for maximizing yield of sugar, which was 0.213 g/g-dry sample. The quantitative analysis by HPLC showed that the soluble carbohydrates in the water phase were mainly composed of glucose. The obtained glucose concentration, 171 mg/L was then fermented at 36 °C for 24 hours by Saccharomyces cerevisae (yeast) to ethanol. Highest yield of ethanol was 0.415 g/g glucose, which was 81.2 % of theoretical yield. Hydrolysis with Sub-CW showed the potential to decompose the cotton textile into simple sugar while keeping sugar degradation to minimal phase and the possibility of complete conversion of cotton textile waste to ethanol via Sub-CW and fermentation

SnSe thin film electrodes prepared by vacuum evaporation: enhancement of photoelectrochemical efficiency by argon gas condensation method

The effect of argon gas condensation (AGC) on crystallinity, surface morphology and photoelectrochemical (PEC) characteristics of SnSe thin films, prepared by thermal vacuum deposition onto ITO/glass substrates, has been investigated. The focal theme was to improve growth process of SnSe thin films and consequently enhance their PEC characteristics, by including argon gas during film manufacturing. For comparison purposes, the films grown With- and Without-AGC were characterized using various techniques such as X-ray diffractometry, UV-VIS spectroscopy, and SEM. The results indicate enhancement in film crystallinity and surface morphology by inclusion of argon gas. Such enhancement has been attributed to slower deposition rate due to argon gas presence. Photoelectrochemical property of SnSe thin film electrodes was studied using linear sweep voltammetry in dark and under illumination. The With-AGC electrodes showed higher photoactivity than the Without-AGC counterparts. Enhancement of PEC characteristics of SnSe With-AGC thin film electrodes is consistent with their crystallinity and surface uniformity. Inclusion of AGC in thermal vacuum deposition processes is potentially valuable to prepare enhanced SnSe thin film electrodes even without the need for further treatment such as etching or annealing

Effect of argon gas on photoelectrochemical characteristics of film electrodes prepared by thermal vacuum evaporation from synthesized copper zinc tin selenide

Copper Zinc Tin Selenide (CZTSe) compound was synthesized from its constituent elements in an evacuated quartz ampoule. The synthesized compound was used as source to deposit film electrodes by vacuum evaporation method under different argon gas flow rates. The argon gas flow rate affected film surface morphology and chemical composition. The film prepared under higher argon gas flow rate of 15 cm3/min or higher exhibited photoelectrochemically p-type behavior due to the SnSe compound. When using argon flow rate of 10 cm3/min or lower, the film exhibited mixed p- and n-type behaviors due to mixed CZTSe and ZnSe phases. The deposited films exhibited high absorption coefficient value (> 4.0 x 104 cm-1) in the wavelength range of 400 and 800 nm, showing their applicability as visible light energy conversion materials. The results show the potential value of the technique described here, where film electrode main characteristics can be controlled by simply changing the argon gas flow rate

Effect of argon gas flow rate on properties of film electrodes prepared by thermal vacuum evaporation from synthesized Cu2SnSe3 source

This work describes a new technique to enhance photoresponse of metal chalcogenide-based semiconductor film electrodes deposited by thermal vacuum evaporation under argon gas flow from synthesized Cu2SnSe3 sources. SnSe formation with Cu-doped was obtained under higher argon gas flow rate (VA = 25 cm3/min). Higher value of photoresponse was observed for films deposited under VA = 25 cm3/min which was 9.1%. This finding indicates that Cu atoms inside the SnSe film were important to increase carrier concentrations that promote higher photoresponse

New technique for efficiency enhancement of film electrodes deposited by argon gas condensation from metal chalcogenide sources

This work describes a new technique to enhance photoactivity of metal chalcogenide-based semiconductor film electrodes deposited by thermal vacuum evaporation under argon gas flow. The experimental work involves controlling a number of parameters such as type of source material (SM = SnSe, Cu2SnSe3 and Cu2ZnSnSe4), substrate temperature (TS = room temperature RT, 100, 200, 300°C), argon gas flow rates (VA = 5, 10, 15, 25 cm3 /min) and temperature of annealing (TA= 150, 250, 350, 450 °C) under nitrogen atmosphere. The effects of varying each parameter on structural, morphological, compositional, photoresponse and optical properties of the deposited electrode were studied. The film deposited at TS = 100 °C under VA = 25 cm3/min from Cu2ZnSnSe4 (CTZSe) source showed highest photoactivity (p %) value 55.7 % compared to films deposited from SnSe (TSe) and Cu2SnSe3 (CTSe) sources, with p % values of 8.3 % and 34.8 %, respectively. Thus, using the quaternary Cu2ZnSnSe4 compound as a source material, offered a new inroad to prepare photoactive thin film electrodes using the argon gas condensation (AGC) technique, simply by varying argon gas flow rate