Microstructural and morphological properties of sputtered Cu(In, Al)Se₂ thin films for solar cell applications

Abstract Cu(In, Al)Se₂ (CIAS) thin films were synthesized by selenization of stacked metallic precursors for different times ranging from 5 to 30 min. Compositional study demonstrates that the Se content in the CIAS thin films is significantly dependent on the selenization time. Both X-ray diffraction and Raman analysis reveal that the selenization time drives structural phase transition from coexisting phases of CuInSe₂ and CIAS to single CIAS phase. The insufficient selenization time during the grain growth process would induce the formation of impurity phase and structural defects in CIAS films. Morphological studies further indicate a gradual transition from the coarse surface containing scattered micron-sized particles to the relatively smooth and compact morphology as the selenization time increases. The solar cell device with the CIAS absorber selenized for 20 min achieves the highest open circuit voltage of 487 mV.