Temperature-dependent growth and characterizations of Cu(In1-xGax)Se2 thin films for photovoltaic applications
摘要
Thin films of Cu(In1-xGax)Se2 (CIGS) were synthesized by thermal annealing of a Cu/In/Ga/Se stack deposited using the multisource sequentially evaporation layer deposition technique. The precursor layers were deposited under a vacuum of ~ 1 × 10–4 Pa using thermal evaporation. The as-deposited stack was annealed at temperatures ranging from 473 K to 623 K, with a 50 K interval, in a vacuum of 10–1 Pa. The nanostructured crystallites of the grown layers were analyzed using X-ray diffraction method. Mixed phases of CuSe, CIGS, and Se were observed at temperatures of 473 K and 523 K, while single-phase CIGS thin films were formed at 573 K and 623 K. The CIGS thin films crystallize in a tetragonal crystal system, with unit cell parameters of a = b = 5.758(7) Å, c = 11.645(3) Å, and a unit cell volume of 386 Å3. The average crystallite size (D) ranges from 16 to 28 nm. The bandgap (Eg) of the CIGS films varies between 1.10 eV and 1.53 eV, while the absorption coefficient spans from 2 × 104 cm−1 to 6 × 104 cm−1 in the entire annealing temperature (TA) range. The single-phase CIGS thin films exhibited a resistivity (ρ) of 2.37 Ω-cm, a mobility (μ) of 4.53 cm2/V-s, and a carrier concentration (NA) of 4.86 × 1014 cm−3 at 573 K, indicating their suitability for use as the absorber layer in solar cell structures.