OPTICAL PROPERTIES AND SURFACE MORPHOLOGY OF Al-DOPED ZINC OXIDE THIN FILM SOLAR CELL

Abstract

The undoped and aluminium-doped (1-4) wt% zinc oxide (ZnO) thin films were fabricated at 40 nm, 100 nm and 150 nm thickness using thermal evaporation method onto corning glass substrates and annealed at 450oC in vacuum for 1 hour. The optical properties were studied using the UV-Vis and photoluminescence spectrums measurements. The morphology and the compositions of the films were observed using atomic force microscopy (AFM) and energy dispersive X-rays analysis (EDAX). The annealed crystalline structure was confirmed using X-ray diffraction (XRD). All the annealed Al-doped ZnO thin films were transparent and showed 80% - 95% transmission in the UV and visible light regions. As the doping increased up to 3 wt% , the optical band gap increased from 4.361 eV (undoped), 4.375 eV (1 wt%), 4.486 eV (2 wt%), 4.491 eV (3 wt%) and 4.416 eV (4 wt %). The emission PL spectra showed three main peaks centered at about 390 nm (UV), 420 nm (blue) and 580 nm (green) at excitation of λ = 290 nm. The intensity of the blue and green peaks decreased as the doping increased. The grain-size of the thin films decreased while the surface roughness increased with increasing aluminium doping.