In the sequential sputtering/selenization process, Ga segregation at the back of Cu(In, Ga)Se2 (CIGS) absorber is frequently observed. In this paper, Ga diffusion in CIGS absorber is investigated during the sputtering and selenization process. Results show that Ga diffusion is closely related to Cu/(In+Ga) ratio in the metallic precursors and the selenization temperature, but barely influenced by Ga/(In+Ga) ratio in the metallic precursors. Based on Fick's second law, a simplified model is established to describe Ga diffusion from the back to the surface of CIGS absorber, which suggests that Ga diffusion coefficient is the dominant factor to constrain Ga content near the absorber surface. By process optimization, Ga/(In+Ga) ratio near the absorber surface is successfully increased. Accordingly, a CIGS solar cell device with efficiency of 12.42% has been obtained.

Pt is a classical catalyst that has been extensively used in fuel cell and solar cell electrodes, owing to its high catalytic activity, good conductivity, and stability. In conventional fiber-shaped solar cells, solid Pt wires are usually adopted as the electrode material. Here, we report a Pt nanoparticle-adsorbed carbon nanotube yarn made by solution adsorption and yarn spinning processes, with uniformly dispersed Pt nanoparticles through the porous nanotube network. We have fabricated TiO(2)-based dye-sensitized fiber solar cells with a Pt-nanotube hybrid yarn as counter electrode and achieved a power conversion efficiency of 4.85% under standard illumination (AM1.5, 100 mW/cm(2)), comparable to the same type of fiber cells with a Pt wire electrode (4.23%). Adsorption of Pt nanoparticles within a porous nanotube yarn results in enhanced Pt-electrolyte interfacial area and significantly reduced charge-transfer resistance across the electrolyte interface, compared to a pure nanotube yarn or Pt wire. Our porous Pt-nanotube hybrid yarns have the potential to reduce the use of noble metals, lower the device weight, and improve the solar cell efficiency.