World energy analysis: H2 now or later?

This is a study of world energy resource sustainability within the context of resource peak production dates, advanced energy use technologies in the transportation and electricity generation energy use sectors, and alternative fuel production including hydrogen. The finding causing the most concern is the projection of a peak in global conventional oil production between now and 2023. In addition, the findings indicate that the peak production date for natural gas, coal, and uranium could occur by 2050. The central question is whether oil production from non-conventional oil resources can be increased at a fast enough rate to offset declines in conventional oil production. The development of non-conventional oil production raises concerns about increased energy use, greenhouse gas emissions, and water issues. Due to the emerging fossil fuel resource constraints in coming decades, this study concludes that it is prudent to begin the development of hydrogen production and distribution systems in the near-term. The hydrogen gas is to be initially used by fuel cell vehicles, which will eliminate tailpipe greenhouse gas emissions. With a lowering of H₂ production costs through the amortization of system components, H₂ can be an economic fuel source for electricity generation post-2040.     

Efficient polymer solar cells based on dialkoxynaphthalene and benzo[c][1,2,5]thiadiazole: A new approach for simple donor-acceptor pair

We reported the synthesis of novel polymeric semiconductor materials based on [poly(4-(5-(1,5-bis(alkoxy)naphthalen-2-yl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PANTBT) and the fabrication of solar cells with a power conversion efficiency of 4.2% using the synthesized polymers blended with [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₀BM) in bulk heterojunction geometry. By varying the side chains, three polymers were synthesized [poly(4-(5-(1,5-bis(2-ethylhexyloxy)naphthalen-2-yl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PENTBT), [poly(4-(5-(1,5-bis(decyloxy)naphthalen-2-yl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PDNTBT), and [poly(4-(5-(1,5-bis(tetradecyloxy)naphthalen-2-yl)thiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PTDNTBT), maintaining a low highest occupied molecular orbital (HOMO) energy level and relatively low band gap, which lead to a high open circuit voltage and short circuit current of the resulting devices. Due to the superior miscibility of PANTBT derivatives with PC₇₀BM, favorable phase separation with a domain size of 10-20 nm was achieved regardless of the crystalline nature of the pristine polymers. PDNTBT with alkyl side chain C10 and PTDNTBT with alkyl side chain C14 showed higher photovoltaic performances. In addition, the effects of the crystalline nature of polymers on the thermal stability of the resulting solar cell devices were discussed in terms of the influence of side chains.     

Optical response of grain boundaries in upgraded metallurgical-grade silicon for photovoltaics

Using upgraded metallurgical-grade silicon (UMG-Si) is a cost-effective and energy-efficient approach for the production of solar cells. Grain boundaries (GBs) play a major role in determining the device performance of multicrystalline Si (mc-Si) solar cells. In this study two UMG-Si wafers, one from the middle part of a brick and the other from the top part of the same brick, were investigated. An excellent correlation was found between the grain misorientation and the corresponding optical response of GBs as indicated by photoluminescence (PL) imaging, electron backscattered diffraction (EBSD), and cross-sectional transmission electron microscopy (TEM). In addition, the PL features at random GBs depend also on the impurity levels in the wafer. In particular the PL emission was greatly enhanced in the narrow regions close to the random GB in the top wafer, which is an interesting phenomenon that may have potential application in high efficiency light-emission diodes (LEDs) based on Si.     

Low band gap poly(1,4-arylene-2,5-thienylene)s with benzothiadiazole units: Synthesis, characterization and application in polymer solar cells

We describe the synthesis of two novel poly(1,4-arylene-2,5-thienylene)s P1 and P2 containing benzo[c][2,1,3]thiadiazole monomeric units via Suzuki-Miyaura polymerization of a thiophene diboronic ester with aryl diiodides. The use of a catalyst complex consisting of Pd(OAc)₂ in combination with the electron-rich biaryl phosphine S-Phos resulted in efficient polymerization reactions. The polymers synthesized, P1 and P2, were characterized by UV-vis spectroscopy and cyclic voltammetry. Theoretical calculations and electrochemical measurements on P1 suggested a favorable position of the molecular orbitals for employment in polymer solar cells in combination with PCBM. Devices containing P1:PCBM 1:2 in the active layer showed an efficiency of 1.2% by simple spin casting from chloroform.     

Parametric cost–benefit analysis for the installation of photovoltaic parks in the island of Cyprus

In this work a feasibility study is carried out in order to investigate whether the installation of large photovoltaic (PV) parks in Cyprus, in the absence of relevant feed-in tariff or other measures, is economically feasible. The study takes into account the available solar potential of the island of Cyprus as well as all available data concerning current renewable energy sources (RES) policy of the Cyprus Government and the current RES electricity purchasing tariff from Electricity Authority of Cyprus. In order to identify the least-cost feasible option for the installation of 1 MW PV park a parametric cost–benefit analysis is carried out by varying parameters such as PV park orientation, PV park capital investment, carbon dioxide emission trading system price, etc. For all above cases the electricity unit cost or benefit before tax, as well as after-tax cash flow, net present value, internal rate of return and payback period are calculated. The results indicate that capital expenditure of the PV park is a critical parameter for the viability of the project when no feed-in tariff is available.     

Composite materials for photovoltaics: A realistic aim?

Layer-type microcrystalline powders of WS₂, MoS₂, WSe₂ and MoSe₂, which were tested for photoeffects with contact free microwave conductivity measurements, were incorporated into a nanostructured TiO₂ matrix in an attempt to obtain macroscopic photocurrents. Even though only 10% of the microcrystals were found to be active in contact with an iodide/iodine solution, photocurrents of the order of 100 μA/cm² to 1 mA/cm² were measured. The photoelectrochemical behavior of microcrystals was studied with space resolved photocurrent and photovoltage measurement techniques and it was attempted to understand the mechanism of current generation via the TiO₂/microcrystal/electrolyte interaction. Critical and still unresolved problems are recognized to be the control and optimization of photoeffects in microcrystals and the adjustment of doping levels of the two material faces. Only small photopotentials could be observed up to now, probably due to an insufficient and inhomogeneous doping of microcrystals. More research will be needed to determine whether this strategy could lead to realistic photovoltaic systems.     

Synthesis and characterization of Cu2ZnSnS4 absorber layers by an electrodeposition-annealing route

An electrodeposition-annealing route to films of the promising p-type absorber material Cu₂ZnSnS₄ (CZTS) using layered metal precursors is studied. The dependence of device performance on composition is investigated, and it is shown that a considerable Cu-deficiency is desirable to produce effective material, as measured by photoelectrochemical measurements employing the Eu^3+/2+ redox couple. The differing effects of using elemental sulphur and H₂S as sulphur sources during annealing are also studied, and it is demonstrated that H₂S annealing results in films with improved crystallinity.     

Optimizing hybrid photovoltaics through annealing and ligand choice

Photovoltaic devices made from blended cadmium selenide nanocrystals with various capping ligands and poly-3-hexylthiophene were prepared. The effects of capping ligands and annealing conditions were investigated. We find that capping ligands determine morphology/phase separation. Our findings suggest that annealing at temperatures between 105 and 122 °C yield optimized devices. We also report CdSe/P3HT blended devices with an efficiency of 1.8% under illumination by AM1.5D.     

Hydrazine-based deposition route for device-quality CIGS films

A simple solution-based approach for depositing CIGS (Cu-In-Ga-Se/S) absorber layers is discussed, with an emphasis on film characterization, interfacial properties and integration into photovoltaic devices. The process involves incorporating all metal and chalcogenide components into a single hydrazine-based solution, spin coating a precursor film, and heat treating in an inert atmosphere, to form the desired CIGS film with up to micron-scaled film thickness and grain size. PV devices (glass/Mo/CIGS/CdS/i-ZnO/ITO) employing the spin-coated CIGS and using processing temperatures below 500 °C have yielded power conversion efficiencies of up to 10% (AM 1.5 illumination), without the need for a post-CIGS-deposition treatment in a gaseous Se source or a cyanide-based bath etch. Short-duration low-temperature (T < 200 °C) oxygen treatment of completed devices is shown to have a positive impact on the performance of initially underperforming cells, thereby enabling better performance in devices prepared at temperatures below 500 °C.     

Deposition of indium tin oxide by atmospheric pressure chemical vapour deposition

We report the deposition of indium tin oxide (ITO) by atmospheric pressure chemical vapour deposition (APCVD). This process is potentially scalable for high throughput, large area production. We utilised a previously unreported precursor combination; dimethylindium acetylacetonate, [Me₂In(acac)] and monobutyltintrichloride, MBTC.[Me₂In(acac)] is a volatile solid. It is more stable and easier to handle than traditional indium oxide precursors such as pyrophoric trialkylindium compounds. Monobutyltintrichloride (MBTC) is also easily handled and can be readily vaporised. It is compatible with the process conditions required for using [Me₂In(acac)].Cubic ITO was deposited at a substrate temperature of 550 °C with growth rates exceeding 15 nm/s and growth efficiencies of between 20 and 30%. Resistivity was 3.5 × 10^− 4 Ω cm and transmission for a 200 nm film was > 85% with less than 2% haze.