**5. CIGS thin film by electrodeposition plus periodical mechanical perturbations**

The strategy of applying mechanical perturbations to the WE during the electrodeposition process was the result of analyzing the morphology of CIGS film produced by electrodeposition using DC potential at the WE; details of film preparation can be found in [13]. As it was shown with the cross-section micrographs, during the initial stage of CIGS film growth, a more compact CIGS layer is produced. This is evident in the as-electrodeposited film and in the annealed film. In order to promote this formation, a mechanical perturbation to the working electrode was applied every 0.066 C/cm<sup>2</sup> during the electrodeposition processes. With the mechanical perturbation, the solution near the WE, producing perhaps turbulent flow, the diffusion layer tends to disappear for a moment and a new nucleation and growth center was originated, and if the perturbation is periodical, the film will be more compact.

**Figure 9(a, b)** shows the typical signal of the WE potential and current density versus time collected during the electrodeposition process by applying periodical mechanical perturbations to the WE. The average current density value was 2.4 mA/cm<sup>2</sup> . The WE potential and the current density were periodically related to the periodicity of the mechanical perturbations. The WE potential had a variation of −1.0 to −0.995 V at each mechanical perturbation. With the periodical mechanical perturbations, it was possible to make CIGS films with 1.2–1.5 μm in 20 min, and the growth was faster with respect to not using mechanical perturbations. The film composition rations were of Ga/(In+Ga) = 0.28 and Cu/(In+Ga) = 0.93. With the mechanical perturbations, no film dissolution was produced as is presented in pulse reverse electrodeposition.

perturbations. Films were grown with two different thicknesses, 1200 and 500 nm, that were subjected to the annealing process. The morphology of the annealed films is shown in **Figure 10(c– f)**. In both cases, it is identified that the films are more compact when it is compared to the one obtained by not using mechanical perturbations during the electrodeposition process. As it can be seen on the micrographs, there is coalescence of grains along the film cross section, and the morphology is dense and crack free. Coalescence is achieved due to the fact that the composition is more homogeneous, zones with copper-poor and cooper-rich have been minimized, and the activation energy for grain growth is more uniform throughout the film. This film morphology is completely different from that obtained without applying mechanical perturbations, where there was only coalescence in the first 300 nm of thickness. This is because a more compact

Mechanical Perturbations at the Working Electrode to Materials Synthesis by Electrodeposition

http://dx.doi.org/10.5772/intechopen.78544

111

**Figure 10.** Micrographs of the surface and cross section of the films that have been grown in a potentiostatic mode with mechanical perturbations. (a,b) without annealing, (c,d) annealed films with a thickness of 1200 nm, and (e,f) annealed

films with a thickness of 500 nm [13].
