Control of Temperature Uniformity During the Manufacture of Stable Thin-Film Photovoltaic Devices

The production of stable thin-film photovoltaic devices requires tight control of temperature uniformity of the glass substrates during the vacuum deposition process. As a first step towards developing an optimized control system for maintaining thermal uniformity as the substrates traverse multiple stations during the deposition process, a finite element thermal model of a single deposition station has been developed. The model couples cavity radiation processes with conduction within the graphite sources and the substrate itself. The effect of adjustable parameters such as radiation shielding, addition of a radiation spreader and varying power distribution among the radiation lamps has been studied. It is concluded that while radiation shielding substantially improves the uniformity, it cannot bring the temperature variation down to the very low levels necessary for producing stable devices. Addition of a radiation spreader improves the uniformity. Seeking and applying the optimum power distribution among the radiation lamps results in more incremental gain in uniformity but a change in lamp configuration is required for attaining the desired uniformity levels.