An infra-red reflecting optical coating for solar cover glass

A major problem with silicon solar cells is that they lose efficiency with increased operating temperature, at a rate of about 0.5% per 1◦C increase. This causes a significant reduction in power output, particularly in hot climates. A solution in the form of an optical coating is presented, which reflects infrared (IR) radiation to limit the module temperature increase. The optical coating is also anti-reflecting (AR) in the visible wavelength range, increasing the amount of light reaching the cell absorber. Modelling results show that the weighted average reflection (WAR) is reduced to 1.22% in the wavelength range associated with the band gap of silicon. The optical coating then reflects up to 70% of the infra-red. Although the model presented is based on silicon, the coating design can be modified to work with other photovoltaic technologies. The coating design uses only 4 layers and can be deposited using conventional high throughput magnetron sputtering systems already familiar to glass manufacturers. Preliminary work on optimising the coating deposition parameters is also presented here alongside modelling results. Deployment of the infra-red reflecting optical coating on solar cover glass represents a potential breakthrough in solar technology and will result in a significant increase in the power output of photovoltaic modules.