Preparation Of Cu（In,Ga）Se₂ Thin Films By Paste Coating

Copper-indium-gallium-diselenide (Cu(In1-xGax)Se2) is one of the most promising semiconductor absorber layer materials among thin-films based solar cells, due to its large optical absorption coefficient, tunable direct band gap and high stability. In this work, CuSe, Ga2Se3 and In2Se3 were used as starting materials and maxed with absolute alcohol, then gound into nanoscale-size pieces by using a ball milling to abtain the required ink for preparing the precursor films. The prepared precursor films were annealed at different temperatures for 30min in Ar atmosphere to yield final (Cu(In1-xGax)Se2)films. The (Cu(In1-xGax)Se2) films were characterized by energy dispersive spectroscopy (EDAX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis spectrophotometer.The EDAX analysis shows the milling technology could control the composition and fabricate Cu(In,Ga)Se2 films of different In/Ga ratio.With the increase of Ga content, the shrinkage of lattice happened, leading to the shift of (112) peak to higher values of 20. The crystallization of the films became worse and the optical band gap became large.The prepared films have shown the chalcopyrite structure When annealed at 250 ℃. With the annealing temperature rising, the binary phase disappeared gradually, the crystallization of Cu(In0.7Ga0.3)Se2 films was more and more better, the grain size became large and their surface morphology was improved. The optical band gap of the prepared films annealed at 500℃ is 1.17 eV.The study of effects of the compaction on mophorlogies of Cu(In0.7Ga0.3)Se2 films indicated that exerting pressure to precursor layers before annealing process can significantly inprove the mophorlogy of final films. The film became smooth but not connected with pressure smaller than 250 MPa. When the pressure was greater than 300 MPa, the film became more smooth and compacted. With pressure increasing to 500 MPa, gaps in films disappeared almost completely.