Liquid phase assisted grain growth in Cu2ZnSnS4 nanoparticle thin films by alkali element incorporation

The effect of adding LiCl, NaCl, and KCl to Cu(2)ZnSnS(4) (CZTS) nanoparticle thin-film samples annealed in a nitrogen and sulfur atmosphere is reported. We demonstrate that the organic ligand-free nanoparticles previously developed can be used to produce an absorber layer of high quality. The films were Zn-rich and Cu-poor, and no secondary phases except ZnS could be detected within the detection limit of the characterization tools used. Potassium was the most effective alkali metal to enhance grain growth, and resulted in films with a high photoluminescence signal and an optical band gap of 1.43 eV. The alkali metals were introduced in the form of chloride salts, and a significant amount of Cl was detected in the final films, but could be removed in a quick water rinse

Nonstoichiometric transfer during laser ablation of metal alloys

Large angular variations in film composition have been found for ablation of a metallic AuCu alloy (Au/Cu ratio ∼1) in vacuum and background gases of Ne and Xe. The AuCu films grown in vacuum at a laser fluence of 5 Jcm−2 exhibit a large loss in the Cu content, with the Au/Cu ratio ∼2.4 at angles close to normal incidence. At this fluence, a distortion of the plume front is observed followed by the appearance of a secondary emission at the substrate, suggesting that resputtering of the film by energetic ions and reflection of ions/atoms at the substrate can lead to a nonstoichiometric transfer in pulsed laser deposition. Further, we have found that depending on the mass of the background gas employed during growth (Ne or Xe), the ratio of elements in the film can vary significantly over a wide range of angles of deposition. In the presence of the light gas Ne, the degree of nonstoichiometric transfer is gradually reduced with increasing background pressure, resulting in a nearly stoichiometric AuCu films at a Ne pressure of 2 mbar. The behavior in the heavy gas Xe is more complex, and both theoretical and experimental data indicate that the loss of Cu in the deposits is caused by the preferential scattering, as well as by backscattering of the light Cu atoms in the plume upon collisions with the background gas