Increase the current density and reduce the defects of ZnO by modification of the band gap edges with Cu ions implantation for efficient, flexible dye-sensitized solar cells (FDSSCs)

Flexible dye-sensitized solar cells (FDSSCs) have good potential in future photovoltaic technology. The spin coating method deposited the ZnO films on indium-tin-oxide-coated polyethylene terephthalate (ITO-PET) flexible plastic substrates. These films are implanted with Cu-ions with 1 x 1013 ions/cm2, 1 x 1014 ions/cm2, and 1 x 1015 ions/cm2. All the films have a hexagonal structure. The film irradiated with 1 x 1014 ions/cm2 showed high crystallinity and crystallite size. Important optical properties like bandgap energy (Eg), band edges, refractive index, extinction coefficient, and dielectric constants are measured by UV-Vis spectroscopy. Bandgap energy decreases, and the refractive index increases at the fluence of Cu ions. The maximum decrease in Eg is observed at the 1 x 1014 ions/cm2 dose. Photoluminescence spectra suggest that defects-related emission peaks are decreased at 1 x 1014 ions/cm2 Cu ions fluency. J-V measurements have significantly improved photovoltaic performance compared to pristine ZnO-based solar cells. The highest efficiency (2.30%) is observed at a 1 x 1014 ions/cm2 dose. The efficiency increase is related to improving the charge transfer ratio and shifting the fermi level toward the conduction band.