Electrical and Structural Characterization of Plasma Polymerized Polyaniline/TiO₂ Heterostructure Diode: A Comparative Study of Single and Bilayer TiO₂ Thin Film Electrode

A heterostructure was fabricated using p-type plasma polymerized polyaniline (PANI) and n-type (single and bilayer) titanium dioxide (TiO₂) thin film on FTO glass. The deposition of single and bilayer TiO₂ thin film on FTO substrate was achieved through doctor blade followed by dip coating technique before subjected to plasma enhanced polymerization. To fabricate p-n heterostructure, a plasma polymerization of aniline was conducted using RF plasma at 13.5 MHz and at the power of 120 W on the single and bilayer TiO₂ thin film electrodes. The morphological, optical and the structural characterizations revealed the formation of p-n heterostructures between PANI and TiO₂ thin film. The PANI/bilayer TiO₂ heterostructure showed the improved current–voltage (I–V) characteristics due to the substantial deposition of PANI molecules into the bilayer TiO₂ thin film which provided good conducting pathway and reduced the degree of excitons recombination. The change of linear I–V behavior of PANI/TiO₂ heterostructure to non linear behavior with top Pt contact layer confirmed the formation of Schottky contact at the interfaces of Pt layer and PANI/TiO₂ thin film layers.