Metal chalcogenide (MX; M = Cd, Cu, and others; X = S, Se or Te) polycrystalline film electrodes of are widely assessed in photoelectrochemical (PEC) solar energy conversions, for many reasons. These films are commonly prepared by chemical bath deposition, electro-deposition or other simple methods, but normally suffer low stability and low PEC conversion efficiency (<1%). Enhancement is being actively investigated. According to US-DOE, maximum conversion efficiency for these electrodes in 2020 is expected to be ~15%. To further enhance the electrode characteristics, we have used two simple strategies. Controlled film annealing and cooling rate is used to enhance particle characteristics (conductivity, interconnection, adherence, band gap value). Each metal chalcogenide film needs specific annealing temperature and cooling rate. To enhance charge transfer across the solid/redox couple interface, electrodes were coated with electro-active materials inside polymeric films, where the electro-active materials behave as charge transfer catalysts. Faster hole transfer to redox couple occurs, which increases photocurrent density. Hole accumulation in the space-charge-layer (responsible for electrode photo-corrosion) is also prevented. By combining both strategies together, metal chalcogenide film electrode stability and efficiency have been remarkably enhanced here. High efficiency values (~12 -18%) have been observed here for metal chalcogenide films. Details of results and their discussions will be described. Theoretical models will also be presented to explain how the modification methods affect both conversion efficiency and film stability. Future prospects of metal chalcogenide film electrodes will be critically discussed.
Keywords: Metal chalcogenide; Solar energy conversion; Charge transfer; Conversion efficiency