Development of an efficient substrate heating assembly for high efficiency CIGS solar cells over 30 cm × 30 cm-area for an in-line pilot evaporation system

In the current studies, the optimization of the uniformity and temperature control across 30 cm × 30 cm area substrates are identified as crucial parameters to form α-phase CIGS in a desired time period, which is the key to deliver high efficiency solar cells at industrial scale. The following attempts were made to achieve a heating system design using: (i) rapid heating by infra-red (IR) lamps, (ii) IR lamps with a graphite susceptor, (iii) a specially designed graphite heater. A three-dimension heat transfer model using COMSOL Multiphysics 4.2a software has been developed and presented to perform the experimental validation on different substrate heating system used here. The following conclusions were drawn from this study: (a) IR lamps can only be used for rapid space heating purpose; (b) IR lamps with intermediate graphite susceptor can only be used to achieve over 10cm×10cm and thus will suffer from intrinsic limitations; (c) the new designed graphite heater can deliver relatively uniform heating across 30 cm × 30 cm area with non-uniformity of ± 5%, which may be acceptable for industrial purpose.