Towards ultrathin copper indium gallium diselenide solar cells: proof of concept study by chemical etching and gold back contact engineering

ABSTRACT An innovative approach combining chemical etching and a “lift‐off” process, which allows back contact processing after CIGSe deposition, permitted to use Au as a highly reflective back contact in ultrathin CIGSe solar cells. The Au back contact does not degrade the other parameters of the cell, as good ohmicity on CIGSe is achieved. An important photocurrent increase compared with regular Mo back contact solar cells is achieved by the enhanced light trapping effect due to the back reflector, leading to an absolute efficiency increase of +2.5% for a CIGSe thickness of 0.4 µm. This approach could be used for further investigations in improving the back side of ultrathin CIGSe solar cells. Copyright © 2012 John Wiley & Sons, Ltd. Ultrathin absorber CIGSe solar cells down to 400 nm are realized with an alternative Au back contact. An innovative combination of chemical etching and “lift‐off” of the absorber is presented. The Au alternative back reflector contact shows a remarkable improvement of the current when compared with the standard Mo back contact, without altering either the voltage or the fill factor. This leads to a +2.5% absolute increase of the efficiency for a 400‐nm absorber CIGSe solar cell.