Multilayer Broadband Antireflective Coatings for More Efficient Thin Film CdTe Solar Cells

Reflection losses limit the efficiency of all types of photovoltaic devices. The first reflection loss occurs at the glass-air interface of the photovoltaic module. If no light trapping mechanism is used about 4% of the solar energy is lost at this surface. Currently, most commercial thin-film CdTe solar modules are manufactured using NSG TEC10 glass, with no light trapping mechanism addressing the reflection at the interface of the glass with the atmosphere. To minimize the losses, a broadband multilayer thin-film coating has been designed and deposited onto the glass surface of a thin-film CdTe solar cell. The coating consisted of four dielectric layers of alternating thin films of ZrO$_{2}$ and SiO$_{2}$. The layers were deposited by using high-rate-pulsed dc magnetron sputtering. Spectrophotometer measurements confirm that the transmission increased by between 2% and 5% over the spectrum utilized by the thin-film CdTe solar cell. The weighted average reflection reduced from 4.22% to 1.24%. Standard test conditions (STC) solar simulator measurements confirmed a 0.38% increase in absolute efficiency and a 3.6% relative increase in efficiency.