The effect of TiO₂ surface modification on the photovoltaic properties of hybrid bulk heterojunction solar cells based on MEH-PPV/CdS/TiO₂ active layer

In this work, we present the synthesis details of uniform shape and size-controlled titanium dioxide (TiO₂) nanorods followed by the deposition of cadmium sulfide (CdS) quantum dots on their surface. The achieved surfactant-capped-TiO2 nanorods as well as CdS/TiO₂ nanocomposites were dispersed in nonpolar solvents, which enabled an easy solution blending with poly (2-methoxy, 5-(2-ethyl-hexy-loxy)-p-phenyl vinylene) (MEH-PPV) conjugated polymer to prepare the active layer of bulk heterojunction solar cells (BHJSCs). The properties of the synthesized capped-TiO₂ nanorods, CdS/TiO₂ nanocomposites, as well as those of their corresponding blends with MEH-PPV were characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), UV-Visible spectroscopy, and photoluminescence (PL) technique. The characterization of the effect of the surfactants (oleic acid, OA, olyamine, OM, and 6-aminohexanoic acid, 6AHA) left on TiO₂ surface and CdS surface modification on BHJSC photovoltaic power conversion efficiency (PCE) showed that: i) for the same surfactants, when CdS was added on the surface of TiO₂ nanorods, the PCE increased due to the higher efficiency of CdS compared to MEH-PPV; and ii) the best PEC was obtained with CdS/OA-6AHA-capped-TiO₂ nanocomposite due to the shortest length of the carbon-chain of 6AHA, leading to higher charge carrier mobility.