After a short introduction to thin film solar cells, I will review what we know about defects in Cu(InGa)Se2 (CIGS), where we found significant differences between Cu-rich and Cu-poor material. By photoluminescence we recently found fundamental differences between pure CIS and Ga containing CIGS: with Ga the recombination is higher in Cu-rich material. And high Ga content CIGS shows a deep defect which gets more and more shallow when we decrease the Ga content. Finally, I will show that we can use photoluminescence to characterise the tails states in kesterite.
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