Enhanced Mo Adhesion on Glass with Cr Interlayers for Copper Indium Diselenide Thin Film Devices

A key element of current Copper Indium Diselenide (CIS) and Copper Indium Gallium Diselenide (CIGS) thin film solar cells is the use of a Mo back contact on soda lime lass (SGL). Because of surface preparation problems, high process temperatures, and mismatch of thermal expansion coefficients, adhesion of the Mo to the soda lime glass can be variable. Also beneficial is the Na facile diffusion of the glass into the absorber layer. We report on the use of thin Cr interlayers to improve the adhesion at the Mo/glass interface. The films were subsequently annealed in vacuum under normal process conditions. Adhesion was excellent and quite uniform for Mo layers with a Cr interlayer of 50 to 800 angstroms compared to control samples without Cr. X-ray Photoelectron Spectroscopy (XPS) data suggests CrO bonding at the glass interface and Cr metallic bonding at the Cr Mo interface. Secondary Ion Mass Spectrometry (SIMS) data for Mo/Cr films shows diffusion of Na throughout the Mo layer identical to that for Mo alone samples. Resistivities of the films have been measured to be 11 μohms-cm, twice that for bulk material of 5.7 μohms-cm. CIGS films were then grown for comparison to films grown on Mo only substrates.