Optical optimization of semi-transparent a-Si:H solar cells for photobioreactor application

To improve the overall photoconversion efficiency and provide energy support for microalgae culture, we propose to develop a photobioreactor (PBR) and photovoltaic technology (PV) coupled system using a-Si:H solar cells directly placed on the PBR's illuminated surface. PV cells have to absorb a part of the incident light to produce electricity while being transparent in the photosynthesis wavelength range. Growing test of Phaeodactylum tricornutum shows that PV optical filtering does not influence the growth rate. Optical modifications of thin solar cells layers thicknesses and reactive ion etching of the glass substrate allowed to maintain a high PV efficiency while maintaining the growth rate of microalgae. The antireflection texture, combined with a light scattering effect applied on the upper side of the substrate gives the best result. Short circuit current of thin solar cells goes from 7.3 to 10.2 mA/cm(2), and the efficiency increased from 3.5 to 4.7%.