Fabrication of selenized/sulfurized Cu(In,Ga)(Se,S)2 solar cells based on high temperature process using high strain point glass substrate

A new high strain point glass substrate for selenized/sulfurized Cu(In,Ga)(Se,S)₂ (CIGS) solar cells was developed. The developed glass has advantages not only higher strain point but also lighter weight and higher mechanical strength than the glass for Plasma Display Panels. CIGS solar cells were fabricated by a selenization/sulfurization 2-step process at high temperature using the developed glass and Soda Lime Glass (SLG) substrates. The SLG needed SiO₂ alkali barrier layer to fabricate CIGS absorber thin film, otherwise delamination occurred. The CIGS fabricated under the high temperatures conditions had better crystal properties, which resulting in higher conversion efficiency than those fabricated at a low temperature of 520 degrees which is commonly used for CIGS solar cells fabrication taking into account the strain point of SLG. The CIGS solar cell fabricated on the developed glass substrate showed higher PV performance than on the SLG with SiO₂ substrate processed on 580 degrees. As a reason of the difference, over 15μm warpage was observed in 30mm length of the SLG substrate, while less than 1μm of warpage occurred in the developed substrate. Our best cell so far is a 0.538-cm² aperture-area efficiency 17.5% using the developed substrate adapting 580 degrees of process temperature.