Fabrication of ZnO:Al/Si Solar Cell and Enhancement its Efficiency Via Al-Doping

In this work, zinc oxide (ZnO) and Al-doped ZnO (0.002, 0.004, and 0.006 wt.%) thin films were prepared by thermal evaporation technique with the thickness of about 125 nm. The X-ray diffraction (XRD) results showed that the prepared films were crystalline with a hexagonal wurtzite structure and preferential orientation in the (002) direction. The crystallite size increased with the increasing of Al doping. Atomic force microscopy (AFM) confirmed that the films grown by this technique had a good homogeneous surface. The roughness average, root mean square value, and the average grain diameter increased with the increasing of Al doping. The optical properties results showed that the transmittance increased with the increasing of Al doping, while the absorbance decreased. The pure and Al-doped ZnO thin films allowed direct energy gap (E_g) that was increased from 3.50 to 3.80 eV with the increasing of Al doping. The electrical properties of the films were studied, and it was found that all the prepared thin films were n-type and the mobility (µ) decreased with the increasing of Al doping. Current–voltage (I-V) characteristics showed that the highest efficiency was 3.64% with V_oc as of  2.8 V,  I_sc as of 3.5 mA/cm² and F.F of  0.371 at the intensity of P =100 mW/cm².