A Tungsten-Titanium (W-Ti) diffusion barrier was prepared on an iron (Fe) substrate by means of magnetron sputtering with subsequent annealing at different temperatures. Rutherford Backscattering Spectrometry (RBS) was used to analyze the Fe distribution in the W-Ti layer. The diffusion constant D-0 = 3.4 x 10(-16) m(2)/s and the activation energy Q = 43 kJ/mol of the Fe diffusing in the W-Ti layer were subsequently calculated based on Fick's Second Law. The results demonstrated that a 291 nm-thick W-Ti barrier layer can be used to block Fe from diffusing into a CIGS solar cell for 20 years at a work temperature of 308 K (35 degrees C). (C) 2015 Elsevier Ltd. All rights reserved.