Sol-gel derived ITO-based bi-layer and tri-layer thin film coatings for organic solar cells applications

摘要

In this investigation, ITO-based bi-layer and tri-layer thin film coatings (similar to 130 nm) were synthesized via a sol-gel spin-coating process and annealed at 500 degrees 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 similar to 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 similar to 91.5% and 3.75 eV for (AgO)I and (I(AgO)I) thin films, respectively. The lowest electrical resistivity of 1.2 x 10(-4) Omega.cm, along with the highest carrier concentration of 11.4 x 10(20) cm(-3) and mobility 40 cm(2)/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.