Efficiency Limits of Underwater Solar Cells

Summary Operation of underwater vehicles and autonomous systems is currently limited by the lack of long-lasting power sources. These systems could potentially be powered using underwater solar cells, but the material requirements to achieve their full potential are not well understood. Using detailed-balance calculations, we show that underwater solar cells can exhibit efficiencies from ∼ 55% in shallow waters to more than 65% in deep waters, while maintaining a power density >5 mW cm−2. We show that the optimum band gap of the solar cell shifts by ∼ 0.6 eV between shallow and deep waters and plateaus at ∼ 2.1 eV at intermediate depths, independent of geographical location. This wide range in optimum band-gap energies opens the potential for a library of wide-band-gap semiconductors to be used for high-efficiency underwater solar cells. Our results provide a roadmap for proper choice of underwater solar cell materials, given the conditions at points of use.