High temperature stability of broadband Anti-Reflection coatings on soda lime glass for solar modules

Reflections from glass surfaces reduce the efficiency of photovoltaic devices. Reflections can be reduced using a broadband Multi-layer Anti-Reflection (MAR) coating. For thin film CdTe modules, the glass is also the substrate. Manufacturers would prefer to use pre-MAR coated glass, so it is essential to establish if the MAR coating can withstand the module production process conditions. Thin film CdTe module fabrication requires temperatures up to ~500°C. Crazing may occur due to mismatch of the thermal expansion coefficients between the glass and the coating materials. The resilience of MAR coatings on soda lime glass, Eagle 2000™ Glass, and NSG TEC™ 7 has been tested by exposure to increasing temperatures up to 800°C to establish the point of failure. SEM imaging and reflection measurements were used to observe the damage caused. Surprisingly, the MAR coating is unaffected up to a temperature of 590oC on soda lime glass substrates and up to 800°C on Eagle Glass. This provides confidence that thin film CdTe module manufacturers can use existing processes with pre-MAR coated glass.