Wide bandgap CIGSe solar cells on transparent substrates above 10% efficiency

This work combines experimental results and modelling assessment of high Ga, wide bandgap CIGSe solar cells fabricated on a transparent glass/TCO substrate yielding efficiencies above 10% without AR coating. An alkali pre-deposition treatment is performed, and the material analysis of the devices by GDOES, XRD and Raman spectroscopy reveals a significant improvement of the Ga incorporation to the matrix in the presence of an alkali element. The optoelectronic characterization of the solar cells reveals an absolute increase by more than two efficiency points for the alkali-doped samples, overcoming the 10% threshold and being, at the time of this work, the highest reported efficiency for a wide bandgap CIGSe solar cell on transparent substrate. The use of the device developed in this study in a full chalcogenide tandem configuration is assessed by numerical modeling, and different improvement pathways for tandem devices are proposed. Specifically, the replacement of the MoSe2 back interlayer by a more transparent MoO3 is deemed critical in tandem configuration.