Spatially resolved photoluminescence measurements on Cu(In,Ga)Se2 thin films

We have measured the spatial dependence of photo luminescence in thin films of Cu-poor Cu(In,Ga)Se-2 with submicrometer resolution. We found large variations in the photoluminescence signal by more than a factor of 5 confined to domains much larger than the typical grain size of 1 mum in the films. Numerical simulation of the diffusion and recombination of photoexcited carriers shows that grain boundary recombination velocities of 10(6) cm/s may lead to approximately 40% variation in the photoluminescence signal. The large differences in photoluminescence efficiency are interpreted in terms of different material phases or defect structures in the off-stoichiometric quaternary chalcopyrite system. From the variation of the photoluminescence intensity at 70 K, we deduced a maximum lateral variation in the quasi-Fermi level splitting of 10 meV. (C) 2002 Elsevier Science B.V. All rights reserved.