A Broadband Multilayer Antireflection Coating for Thin Film CdSeTe/CdTe Solar Cells

Thin film cadmium telluride (CdTe) photovoltaics (PV) is the most successful second-generation PV technology, with a current installed capacity of over 30 GWp, predominantly at utility scale. Recent improvements in the buffer layer of the device, switching from cadmium sulphide (CdS) to transparent magnesium-doped zinc oxide (MZO), tin oxide (SnO_{2}), or zinc oxide (ZnO), and the addition of selenium to the absorber layer, have expanded the wavelength range over which CdTe devices operate, from 400-850 nm to 350-900 nm. These changes have resulted in higher efficiency devices. As a result, an optimized antireflection (AR) coating design is required to improve the efficiency further. A six-layer AR coating of SiO_{2} and ZrO_{2}, building on a previous four-layer design for CdTe devices, has been designed, modeled, and fabricated on 3.8-mm thick fluorine-doped tin oxide coated TEC™15 substrates, reducing reflection by 3.38% absolute. Electrical measurements of a CdSeTe/CdTe device before and after addition of the AR coating show an increase in short-circuit current density (J_{sc}) of almost 1 mAcm^{-2}, a relative increase of 3.45%, and a 0.6% increase in the conversion efficiency of the device, from 16.93% to 17.53%, which is a relative increase of 3.54%. Unlike conventional single layer AR coatings this multilayer coating is stable even under the high processing temperatures required in module manufacturing, so could be supplied by glass manufacturers. This newly optimized broadband AR coating on will enable significantly higher conversion efficiencies and help push CdSeTe/CdTe module efficiencies higher.