We are also interested in moving the prototype device from a laboratory scale (< 1 cm2) to a large-scale practical device (50-100 cm2). Here, synthesis procedures capable of large scale fabrication are used (e.g., spray pyrolysis, sputtering, CVD). At this scale, engineering challenges (e.g., Ohmic losses, pH gradient) dominate over materials limitations. We collaborate with our partners to investigate various device designs that overcome these limitations and result in optimized performance.