Statistical process control driven variation reduction critical to manufacturing success

The manufacture of state of the art production solar cells introduces sources of variation that are both omnipresent and potentially devastating to the product quality as measured by solar cell performance variation. Towards minimizing these sources of variation, Shell Solar has chosen an approach that considers all reasonable sources of variation as potential parameters for formal statistical process control (SPC). The milestones for improvement of a given parameter are: 1) establish SPC, 2) demonstrate statistical control and 3) demonstrate statistical capability. The strategy chosen for variation reduction at Shell Solar is a particular application of statistical process control. SPC is the application of statistical methods to measurement and analysis of process variation. It applies to both in-process parameters (e.g. firing time at peak temperature) and product parameters (e.g. Voc). There are those who use the term SPC for techniques that do not involve the use of statistics. We believe that statistical treatment of the data is necessary for effective SPC. Through the use of specific examples within the Shell Solar cell processing line we will demonstrate the use of SPC, the reduction of cell variation, and the ultimate improvement of both variation and cell performance made possible using these techniques.