Indium tin oxide and gold nanoparticle solar filters for concentrating photovoltaic thermal systems

The combination of concentrating solar power and photovoltaic technologies in hybrid photovoltaics thermal systems have the potential of increasing the overall efficiency of solar energy by utilizing non-Photovoltaic wavelengths as dispatchable thermal energy for use as industrial process heat and/or electricity generation using a thermal engine. One way of achieving this requires a thermally-stable spectral filter capable of effectively transmitting photovoltaic radiation while absorbing non-Photovoltaic radiation. Here, we utilize indium tin oxide and gold nanoparticles in a silane-based heat transfer fluid capable of withstanding temperatures up to 340 °C while maintaining spectral transparency at photovoltaic wavelengths. To promote compatibility with the heat transfer fluid and achieve greater thermal stability of the nanoparticles, surface modifications were performed for both the indium tin oxide and the gold nanoparticles. It was found that the greatest solution stability was achieved with the use of a (6–7% aminopropylmethylsiloxane)-dimethylsiloxane copolymer surface ligand. Interestingly, when heating the nanoparticles, a spectral blue-shift was observed in the localized surface plasmon resonance peaks of both nanoparticles along with an increase in absorptivity for indium tin oxide. Analysis of the filter performance revealed that a filter optimized for c-Si photovoltaic receiver transmits 73% of bandgap radiation and absorbs 78% of sub-bandgap radiation. The increasing solar absorption properties of the nanoparticle at higher temperatures helped the filter maintained an ideal performance up to 250 °C, even with lower concentrations of nanoparticles. At 300 °C, however, the filter performance reduced due to the disappearance of the gold peak, which is attributed to the inferring free tin ions.