A method of processing a plurality of photovoltaic materials in a batch process includes providing at least one transparent substrate having an overlying first electrode layer and an overlying copper species based absorber precursor layer within an internal region of a furnace. The overlying copper species based absorber precursor layer has an exposed face. The method further includes disposing at least one soda lime glass comprising a soda lime glass face within the internal region of the furnace such that the soda lime glass face is adjacent by a spacing to the exposed face of the at least one transparent substrate. Furthermore, the method includes subjecting the at least one transparent substrate and the one soda lime glass to thermal energy to transfer one or more sodium bearing species from the soda lime glass face across the spacing into the copper species based absorber precursor layer via the exposed face.