CGS thin films solar cells on transparent back contact

The goal of this work is to fabricate and study wide gap CuGaSe2 solar cells to be used as top cell of a mechanically stacked tandem device. CuGaSe2 CGS absorber thin films are prepared by co evaporation in a three stage process onto Mo soda lime glass substrates and onto different transparent conductive oxides TCOs SnO2 F FTO and In2O3 Sn ITO . Laser Light Scattering LLS is used as an in situ process control. A deterioration of the transparency of the TCOs is observed after CGS deposition, especially for the ITO. The cell performance is lower for devices on TCOs due to the increased resistivity of the transparent back contact which leads to a decrease in fill factor FF . The Cu content during the process appears as a critical parameter to control the optical transmission as well as the efficiency of the device. Quantum efficiency measurements also reveals a smaller minority carrier collection for the solar cells grown on TCOs. A total area efficiency of 4.2 for a device on FTO is achieve