Full day simulations of anti-reflection coatings for flat plate silicon photovoltaics

This paper presents an investigation into the use of thin films of silicon oxide and silicon nitride as anti-reflection coatings to minimise the reflection losses of incident solar insolation on silicon photovoltaic cells. The total theoretical reflectance under two insolation cases is investigated. Firstly, with AM 1.5 direct beam radiation at normal incidence, as is usually simulated, and secondly, with the direct beam simulated over a full day. Ensuring that a minimum silicon oxide layer of 20 nm is deposited on the silicon wafer for surface passivation, variations in optimised film thicknesses between both simulations were approximately 4%. The theoretical results also showed a strong correlation to experimental results for the normal incident case. The results demonstrate that surfaces optimised for normally incident radiation are adequate for non-tracking photovoltaic cells under real conditions. The seasonal variations of an optimised surface showed variations in a performance of less than 0.1%. We have also demonstrated that the excellent surface passivation obtained with a thin thermal oxide is maintained after depositing a silicon nitride layer using low-pressure chemical vapour deposition.