Preparation, deposition of Cu(In1−xGax)Se2 nanopowder thin films by non-vacuum processes and its characterization

Non-vacuum techniques for the preparation of Cu(In_1-xGa_x)Se₂(CIGS) nanoparticle films is reported. CIGS nanoparticles were prepared by mechano-chemical process followed by screen printing and air-brush spray with suitable solvent. Elemental Cu/In/Ga/Se sources were ball milled with different milling times and rates to optimize the conditions to obtain chalcopyrite composition. Under the optimized conditions, gallium composition was varied from x=0.1-0.5 to obtain single phase CIGS nanoparticle. XRD revealed the polycrystalline and chalcopyrite structure with an intense (112) orientation. Grain sizes varied from 8 to 20 nm and 2θ values of (112) plane shifted towards higher angle confirming the gallium incorporation into indium sites. TEM/HRTEM analyses revealed the presence of nanocrystalline particles and SAED pattern correspond to peaks found from XRD, d-spacing values were found to be 1.06, 3.33, 2.03 and 0.906Å corresponding to the diffraction patterns and simulated patterns are matched with HRTEM planes. Raman spectra showed intense peak at 168-172cm^-1, corresponding to chalcopyrite structure. Viscosities, ratio of solvents versus nanopowders were optimized, in order to make films using screen printing and air brush spray. Screen printed films were annealed in N₂ atmosphere from 300-400° C and no significant growth in particle size observed. Loss of gallium was estimated from EDAX and peak value (2θ) of the plane (112) shifted towards left. Hall studies yielded the carrier concentration of 10¹⁴ cm^-3 and dielectric constant decreased with increase in frequency and increased with temperature (298-398K). Photoconduction studies revealed an increase in current with light intensity/thickness. Glass/ITO/CdZnS/CIGS/Ag device was made and characterized by I-V yielding open circuit voltage 300 mV, short circuit current density, 126.7 μA cm^-2 - nd fill factor close to 0.25.