Sol-gel derived ITO-based bi-layer and tri-layer thin film coatings for organic solar cells applications
Applied Surface Science
School of Engineering
University of Baghdad
© 2020 Elsevier B.V. In this investigation, ITO-based bi-layer and tri-layer thin film coatings (~130 nm) were synthesized via a sol-gel spin-coating process and annealed at 500 °C. Thin layers of Au, Au-NPs, Ag-NPs and AgO were inserted underneath ITO films to form bi-layer thin film systems and/or encapsulated between two thin ITO layers to form tri-layer thin film systems. The effects of incorporating these layers with ITO thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), UV–Vis spectroscopy, four-point probes and Hall effect. XRD results confirmed the presence of a body-centred cubic structure of indium oxide for all synthesized ITO-based coatings with an average grain size ~30 nm. FESEM images of all fabricated films revealed the formation of dense surfaces with grain-like morphologies confirming the formation of a polycrystalline structure of ITO. Optical studies on the Ag-NPs and Au-NPs colloidal solutions resulted in absorption peaks featured at wavelengths 405 and 531 nm, indicating the formation of 10–14 nm and 48 nm Ag and Au nanoparticles, respectively. The highest optical transparency and band gap energy were found to be ~91.5% and 3.75 eV for (AgO)I and (I(AgO)I) thin films, respectively. The lowest electrical resistivity of 1.2 × 10−4 Ω·cm, along with the highest carrier concentration of 11.4 × 1020 cm−3 and mobility 40 cm2/V.s were obtained from the IAuI thin film. An improvement in the power conversion efficiency (PCE) from 3.8 to 4.9% was achieved in an organic solar cell by replacing the conventional pure ITO electrode with the (I(AgO)I) electrode.