A research team at the University of Wisconsin-Milwaukee (UWM) has discovered that zinc-phosphate-hydrate (ZPH) films coated onto metals create a photovoltaic effect.
Their work is presented in the research paper “Fabrication and study of H2O-incorporated zinc-phosphate films interfaced with organic dye and their photo-detection characteristics,” available in the journal Applied Physics Letters.
The researchers set out to test hopeite, a zinc-based mineral used for corrosion protection, when they observed that layers of hopeite can react quickly to changing light conditions, allowing for the production of electricity from light.
The research paper explains that ZPH films grown on electrically conductive indium tin oxide (ITO) substrate exhibited a layered morphology with interlayer distances of 20 nm to 30 nm. The researchers explain that the light emission spectrum is dominated by a narrow UV band at 378 nm, with a full width at half maximum of 16 nm.
The team fabricated and tested around 20 devices and found variations in film thickness to be the primary hurdle for reproducibility, with increased thickness and non-uniformity leading to reduced photocurrent. Their photoluminescence excitation data found a sharp cutoff edge at around 447 nm, corresponding to a bandgap of 2.77 eV.
Further exploration found that the ZPH films’ photovoltaic effect was amplified when combined with anthocyanin, a natural dye found in blackberries, as the pigment alters how the mineral interacts with light, helping to boost voltage output.
The research paper details that the ZPH films generated a photovoltage of up to 281 mV under white light when interfaced with the anthocyanin dye, demonstrating how the electrolyte enhances the rate of photogenerated charge transfer.
The device was tested under repeated on/off illuminations and steady state, the research paper adds, with the device reaching a zero-bias photo-to-dark current ratio nearing 97.5, alongside photocurrent rise and decay constants of 0.4 s and 10.8 s.
The researchers noted that their fabricated films differ from traditional solar cells as they do not require semiconductors or an external power source to convert light into electrical current. This led the team to conclude the results could open doors to more affordable solar cells.
“These findings confirm that ZPH-based inorganic–organic interfaces, akin to conventional semiconductor junctions, hold strong potential for low-cost photovoltaics and self-powered UV–visible photodetectors operating in the sub-kHz frequency range,” the research paper concludes.
The researchers have filed for a patent through the UWM Research Foundation.
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