Widespread adoption of solar energy technologies, such as solar photovoltaics (PV) and/or photoelectrochemical (PEC) hydrogen fuel production cells, requires low-cost fabrication methods to produce large area devices for solar energy harvesting. Novel thin-film semiconductor materials produced from chemical solution deposition have significant potential to reduce production and manufacturing costs. Ongoing research at James Madison University is focused on the development and fabrication of thin-film semiconductor materials for PV and PEC applications. Thin-film semiconductors, such as BiVO 4 and Cu 2 ZnSnS 4 , are fabricated by depositing a liquid precursor solution onto a heated substrate using ultrasonic spray pyrolysis, pneumatic spraying, or liquid drop casting. To enable thin-film depositions over larger sample areas, an automated deposition system is being developed. This coating system is comprised of two primary and interacting subsystems: motion and heating control. The motion system controls the path and travel speed of the precursor deposition device, such as the ultrasonic spray nozzle, during the deposition process. During the deposition procedure, the substrates rest on a heated surface, which provides the energy necessary to induce the desired chemical reactions on the substrate and remove unwanted compounds. This surface have a uniform spatial temperature distribution and must be controlled to a constant temperature ranging from 40 °C to 500 °C with a variability of ±4 °C. A specially designed heating plate was designed to meet these requirements. The focus of this work is to design an integrated system that allows a deposition area of 16 in 2 to be completed at James Madison University.

The effect of tungsten doping and hydrogen annealing treatments on the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) photoanodes for solar water splitting was studied. Thin films of BiVO4 were deposited on ITO-coated glass slides by ultrasonic spray pyrolysis of an aqueous solution containing bismuth nitrate and vanadium oxysulfate. Tungsten doping was achieved by adding either silicotungstic acid (STA) or ammonium metatungstate (AMT) in the aqueous precursor. The 1.7 μm – 2.2 μm thick films exhibited a highly porous microstructure. Undoped films that were reduced at 375 ºC in 3% H2 exhibited the largest photocurrent densities under 0.1 W cm-2 AM1.5 illumination. This performance enhancement was believed to be due to the formation of oxygen vacancies, which are shallow electron donors, in the films. Films doped with 1% or 5% tungsten from either STA or AMT exhibited reduced photoelectrochemical performance and greater sample-to-sample performance variations. Powder X-ray diffraction data of the undoped films indicated that they were comprised primarily of the monoclinic scheelite phase while unidentified phases were also present. Scanning electron microscopy showed slightly different morphology characteristics for the Wdoped films. It is surmised that the addition of W in the deposition process promoted the morphology differences and the formation of different phases, thus reducing the PEC performance of the photoanode samples. Significant PEC performance variability was also observed among films deposited using the described process.