Dielectric and diffusion barrier multilayer for Cu(In,Ga)Se2 solar cells integration on stainless steel sheet

For the fabrication of monolithically integrated flexible Cu(In, Ga)Se2, CIGS modules on stainless steel, individual photovoltaic cells must be insulated from metal substrates by a barrier layer that can sustain high thermal treatments. In this work, a combination of sol-gel (organosilane-sol) and sputtered SiAlxOy forming thin diffusion barrier layers (TDBL) was prepared on stainless steel substrates. The deposition of organosilane-sol dielectric layers on the commercial stainless steel (maximal roughness, Rz = 500 nm and Root Mean Square roughness, RMS = 56 nm) induces a planarization of the surface (RMS = 16.4 nm, Rz = 176 nm). The DC leakage current through the dielectric layers was measured for the metal-insulator-metal (MIM) junctions that act as capacitors. This method allowed us to assess 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 on sol-gel double layers. A yield of 100% was achieved for sol-gel double layers reinforced with a sputtered SiAlxOy coating and a third sol-gel monolayer. Since this yield is obtained on several samples, it can be extrapolated to any substrate size. Furthermore, according to Glow Discharge Optical Emission Spectroscopy and Time of Flight Secondary Ion Mass Spectroscopy measurements, these barrier layers exhibit excellent barrier properties against the diffusion of undesired atoms which could otherwise spoil the electronic and optical properties of CIGS photovoltaic cells.