Cu in In2S3: interdiffusion phenomena analysed by high kinetic energy X-ray photoelectron spectroscopy



Chalcopyrite thin film solar cells with an In2S3 buffer showed high efficiencies above 15%, but only after annealing at 200 °C. One possible explanation is a Cu interdiffusion at the absorber/buffer interface. We were able to directly measure a Cu interdiffusion with a new tool at the BESSY synchrotron facility: HIKE (high kinetic energy X-ray photoelectron spectroscopy). Due to its increased information depth of up to 10–20 nm HIKE is able to provide chemical information even through thin closed overlayers. The HIKE endstation also allows in-situ heating. A layer stack of In2S3/ Cu(In,Ga)Se2 was prepared and heated in-situ up to a temperature of 300 °C while continuously measuring HIKE spectra. A strong increase of the Cu signal above temperatures around 200 °C was found. With this setup we were able to directly monitor the Cu diffusion from the absorber into the buffer layer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)