A broadband anti-reflection 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 market share of 5 % and deployment predominantly at utility scale. Improvements in the buffer layer of the device, switching from cadmium sulphide (CdS) to tin oxide (SnO2) or magnesium-doped zinc oxide (MZO), and the addition of selenium to the absorber layer, have expanded the wavelength range over which CdTe devices operate, from 400-850nm to 350-900nm, resulting in increased efficiency. As a result, an optimised anti-reflection (AR) coating design is required to improve the efficiency even further. A 6-layer AR coating of SiO2 and ZrO2, building on a previous 4-layer design for CdTe devices, has been designed, modelled, and fabricated on 3.8mm thick FTO-coated TEC15 substrates, reducing reflection by 3.38 % absolute. Electrical measurements of a CdSeTe/CdTe device before and after addition of the AR coating show a relative increase in short-circuit current density, Jsc, of 3.45%, and a relative increase in efficiency of 3.54 %. The use of this AR coating on CdSeTe/CdTe PV devices, which is stable under the high processing temperatures required in device manufacturing, will enable significantly higher conversion efficiencies.