Teflon® FEP frontsheets for photovoltaic modules: Improved optics leading to higher module efficiency

Increasing the amount of light that reaches the cell is one approach to improved photovoltaic (PV) module efficiency. In current designs using weathering layers of glass or poly(co- ethylene-tetrafluoroethylene) (Teflon® ETFE), some light is lost due to reflection and scattering due to haze. Teflon® FEP, poly(co- tetrafluoroethylene-hexafluoropropylene), offers both a lower index of refraction and higher transparency than existing front sheet materials for modules, leading to improved efficiency and greater output of current and power. In precise optical measurements, we showed that FEP delivers more light to the underlying PV cells. By modeling the optical transmission data for front sheets of glass, ETFE, and FEP, one can demonstrate an improvement of 1.5-3% in short circuit current output when using FEP, depending on the cell technology. Initial module experiments have confirmed model predictions and demonstrate the power output performance enhancement when using FEP.