Novel high thermal barrier layers for flexible CIGS solar cells on stainless steel substrates

Abstract

For the fabrication of monolithically integrated flexible CIGS modules on stainless steel, individual photovoltaic cells must be insulated from the metal substrates by a barrier layer that can sustain high temperature treatment. In this work combination of sol-gel (organosilane-sol) and sputtered SiAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> thin layers (TDBL) were prepared on stainless steel substrates. At first, the deposition of organosilane-sol dielectric layers on the commercial AISI-316-2RB stainless steel (Rz = 500 nm, RMS= 56 nm) induces a planarization of the surfaces (RMS = 16.4nm, Rz =176nm). The leakage current in DC mode through the dielectric layers was measured by preparing metal-insulator-metal (MIM) junction that acts as capacitor. This method proposed here allowed us to quantify the quality the quality of our TDBL insulating layer and its lateral uniformity. Indeed, evaluating a ratio of the number of valid MIM capacitors to the number of tested MIM capacitors, a yield of ~ 95% and 50% has been reached respectively with non annealed and annealed samples based sol-gel double layer. A yield of 100% has been reached with reinforced PCDP by sputtered SiAl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> thin layer showing perfect electrical insulation. Since this yield is obtained on several samples, it can be extrapolated to any substrate size. Furthermore, according to Glow Discharge Optical Emission Spectroscopy (GDOES) measurements, these barrier layers exhibit excellent barrier properties against the diffusion of undesired atoms which could spoil the electronic and optical properties of CIGS based photovoltaic cells.