Band offset at TiO2/MDMO PPV and TiO2/PEDOT PSS interfaces studied using photoelectron spectroscopy

Abstract

We report band alignment and band offset studies across the interfaces of hetero-structures of TiO₂ with poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)-p-phenylene vinylene] (MDMO PPV) and poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT PSS) using photoelectron spectroscopy. In both the cases the band alignment was found to be type II with significant band bending in the range 0.2 to 0.3 eV. In the case of the TiO₂/MDMO PPV hetero-structure, the valance band offset (VBO)/conduction band offset (CBO) were found to be 2.68 ± 0.1 eV/1.68 ± 0.1 eV, while the TiO₂/PEDOT PSS hetero-structure exhibited VBO/CBO as 2.3 ± 0.1 eV/0.7 ± 0.1 respectively. Based on these results, schematic band diagrams for these organic/inorganic hetero-structures were proposed. Our studies are important for the optimum design of various photovoltaic devices based on these organic/inorganic hetero-junctions.