One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near‐edge region can be fitted to a simple expression in which the intercept gives the band‐gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called “Tauc” plots). While the technique is powerful and simple, the accuracy of the fitted band‐gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure‐of‐merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.

ZnO was used by Viezbicke et al. (pp. http://doi.wiley.com/10.1002/pssb.201552007) for assessing the accuracy of the Tauc method for band‐gap determination. This method is based on optical absorption data: longer wavelengths are barely absorbed, but wavelengths shorter than the band‐gap cut‐off are absorbed progressively more strongly, as illustrated schematically for three particular photon energies (upper left). These photons excite gradually wider direct transitions within the material's electronic structure (upper right) yielding larger absorption coefficient values. Direct‐gap materials like ZnO show a linear region in the (αhν)2 vs. Ephoton plot, which is extrapolated back to the x‐axis to find the threshold band‐gap value (lower right). Viezbicke et al. examined a large population of these bandgap determinations leading to an improved understanding of the accuracy of the method. Finally, an easily‐evaluated figure‐of‐merit was defined that may help guide more accurate Tauc fitting in the future. For samples with relatively sharper Tauc plot shapes the data found Eg(ZnO) to be 3.276 ± 0.033 eV, in good agreement with data for single crystalline material (lower left).

Copper bismuth sulfide, Cu 3 BiS 3 , has been prepared by a solvothermal method that relies on precursor complexing to achieve the desired ternary chalcogenide preferentially over possible binary sulfides in the system. The complexing agent L-cystine also simultaneously donates sulfur to the compound when the complexes are dissociated at a single temperature. This low temperature and use of nitrate salts instead of the commonly employed but less "green" chloride salts provide a path toward cleaner methods. The reaction progression has been characterized by X-ray powder diffraction of sequential samples and shows complete reaction of reagents to form the Wittichenite phase. Spectroscopy analysis reveals confirmation of a direct bandgap at approximately 1.5 eV. Microscopy images reveal varying morphology dominated by nanorods and including particles with aspect ratios approaching 1:1. A low-temperature Cu 3 BiS 3 synthesis employing L-cystine as a sulfur source and complexing agent, nitrate salt precursors, and pure ethylene glycol has been demonstrated. ■ INTRODUCTIONIncreasing attention is being directed toward the development of alternative and earth-abundant semiconductors for photovoltaic and other optoelectronic applications. One promising class is the I−V−VI family that includes Cu 3 BiS 3 . Naturally occurring in the "Wittichenite" mineral form, 1 the compound is stable for a broad range of processing temperatures. 2,3 As such, various techniques have been employed to synthesize Cu 3 BiS 3 and other ternary sulfide films and nanostructures. Sputtering, 4−9 coevaporation, 10−12 and solid-state reactions 9,13,14 have been successful in producing stoichiometric compounds depending on the nature of the processes. Solution-based syntheses of both hydrothermal 15 and solvothermal 9,16−20 routes have been demonstrated with a range of precursors. While most rely on thermal heating to exceed the reaction threshold, microwave heating has also been demonstrated. 20 Solution-based synthesis of ternary chalcogenides also brings with it the risk of producing counterproductive binary compounds. Strong reducers are often employed to facilitate and expedite ternary syntheses, but their toxicity is a growing concern if any process is to be scaled for manufacturing. In a rising trend toward green synthesis, the employment of biological complexing agents has been successful. The use of L-cystine as a sulfur donator was demonstrated for Sb 2 S 3 , 17 and its use as a complexing agent for the ternary Cu 3 SbS 3 system followed quickly. 19 The Cu 3 BiS 3 morphologies produced in a similar fashion have resulted in varying morphologies, including dendrites, 14,20 rods, 21 and flower (or coral) like structures. 18,22 There remains until now a lack of Cu 3 BiS 3 synthesis employing a solvothermal system, L-cystine as a sulfur donator and a complexing agent, radiant heating, and nitrate salt precursors; this new and useful method is presented here. ■ EXPERIMENTAL SECTIONReagents. All chemicals in this work were used as obtained and in...

Building practical plug-in electric vehicles is under way at many car companies around the world, though it is expected that they will not be widely available in the USA for quite some time. The ultimate vehicle cost is controlled substantially by the battery storage capacity required and this, in turn, is governed by the vehicle size and performance expected by consumers. The present paper examines the specific situation where existing hybrid vehicles might be converted to plug-in functionality by adding a supplementary battery pack to extend the driving range while keeping the electric/gasoline hybrid drive-train intact. We examine fuel efficiency from the standpoint of vehicle weight to extract system parameters that quantify the extra fuel consumption associated with driving a slightly heavier vehicle after plug-in conversion has been effected. We show that only modest additional battery capacity is required to meet most commuter needs in a cost-effective manner. , III (2011) 'Understanding parasitic energy costs for PHEV conversion packs as we move toward V2G', Int.

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