How low can you go? The lower limits of platinum loading, in the sub‐monolayer to monolayer range, have been explored for the hydrogen evolution reaction (HER). A low‐cost substrate material, tungsten monocarbide (see picture; W blue, C small gray spheres) is capable of supporting monolayer amounts of platinum (large blue‐gray spheres) to produce an electrocatalyst with the same HER activity as bulk platinum.

Thin-film solar cells have been fabricated from Cu(InGa)Se2 films which were deposited by four-source elemental evaporation with [Ga]/([In]+[Ga]) from 0.27 to 0.69 corresponding to a band gap from 1.16 to 1.45 eV. The films were intentionally deposited with no grading of the Ga and In to avoid gradients in their electrical and optical properties. X-ray diffraction, energy-dispersive x-ray spectroscopy, and Auger electron spectroscopy show that the films have uniform composition with no change in structure and morphology. Glass/Mo/Cu(InGa)Se2/CdS/ZnO devices have open-circuit voltage increasing over the entire band gap range to 788 mV and 15% total area efficiency for band gap less than 1.3 eV, or [Ga]/([In]+[Ga]) less than 0.5. A decrease in device efficiency with higher Ga content is caused primarily by a lower fill factor. Analysis of current–voltage and quantum efficiency measurements show that this results from a voltage-dependent current collection.

Single-bath electrodeposition of polycrystalline Cu͑In,Ga͒Se 2 thin films for photovoltaic applications is described. Cu͑In,Ga͒Se 2 was deposited onto Mo electrodes from low concentration aqueous baths containing CuCl 2 , InCl 3 , GaCl 3 , and H 2 SeO 3 . Buffering the solutions to pH ϳ 2.5 stabilized bath chemistry and improved Cu͑In,Ga͒Se 2 film composition. Bath concentrations were shown to affect composition of deposited films, with a bath ͓Se 4+ ͔/͓Cu 2+ ͔ ratio of 1.75 required to maintain suitable deposited Se and Cu levels, while ͓In 3+ ͔ could be adjusted to control deposited In and Ga. Deposited films initially exhibited significant cracking, which was prevented by lowering the ͓Se 4+ ͔ in the bath, and contained Cu 2−x Se as secondary phases, resembling cauliflower florets, embedded in the film surfaces. The formation of these secondary phases was overcome by pretreating the Mo electrodes with a short 1 min deposition from the Cu͑In,Ga͒Se 2 bath. This, coupled with a multipotential deposition regime, led to growth of smooth, compact, crack-free films of near stoichiometric values. Mechanisms of film growth and morphology control are discussed. All as-deposited films exhibit low crystallinity, and for device processing require recrystallization by annealing in an H 2 Se atmosphere. Promising preliminary results of electrodeposited Cu͑In,Ga͒Se 2 devices are presented.Polycrystalline Cu͑In,Ga͒Se 2 has exhibited very promising performance for thin film photovoltaic ͑PV͒ application, now exceeding 19% conversion efficiencies at the laboratory scale. 1,2 The best quality devices, hitherto, have been processed using high vacuum based techniques. 2 However, there is an interest in developing deposition techniques that avoid the use of high vacuum, especially when considering scale-up to industrial processing levels. Electrodeposition requires only off-the-shelf, low cost equipment and allows deposition over large areas at low temperature conditions, good control of film thickness, and potentially high utilization of bath species. The high absorption coefficient of Cu͑In,Ga͒Se 2 ͑ϳ10 5 cm −1 ͒ allows thin films, Ͻ2 m, to be applied to PV devices. Electrodeposited CdTe PV devices have been successfully processed, reaching near commercial performance. 3 A number of groups have reported electrodeposition-based processing of CuInSe 2 and Cu͑In,Ga͒Se 2 films, employing a number of approaches: sequential deposition of individual metal films, 4 deposition of various precursors, 5-7 and single-step deposition, where all elements are deposited simultaneously. 8 Single-step deposition processes are appealing in order to simplify device manufacture. The successful deposition of CuInSe 2 from a single electrochemical bath onto a range of different substrate types has been previously reported, 8-19 and a few groups have attempted to describe bath chemistry and mechanisms of film growth. 9,11,20-22 As-deposited films are generally of low crystallinity, and a post-deposition anneal, often in a selenium-containing atmosphere, ...