Poor performance of CdS/CdTe material near the edges of 30×30 cm cells has been observed. This was correlated to poor recrystallisation of the ‘edge material’ upon annealing. Various techniques — XRD and GAXRD, TEM, SIMS and XPS — have been used in order to carefully map differences in as-deposited material across the cell surface that could be responsible for this effect. The results revealed that there is a subtle difference in the structure of the CdTe near the cell edges, with the edge material actually being in a slightly better state of crystallisation and material from the cell centre being very defective. Recrystallisation is essential for achieving good cell operation and the driving force behind CdTe recrystallisation upon annealing is probably this high defect density.