Deciphering Electron Interplay at the Fullerene/Sputtered TiO_<i>x</i> Interface: A Barrier-Free Electron Extraction for Organic Solar Cells

Abstract

Organic photovoltaics (OPVs) technology now offers power conversion efficiency (PCE) of over 18% and is one of the main emerging photovoltaic technologies. In such devices, titanium dioxide (TiO_<i>x</i>) has been vastly used as an electron extraction layer, typically showing unwanted charge-extraction barriers and the need for light-soaking. In the present work, using advanced photoemission spectroscopies, we investigate the electronic interplay at the interface between low-temperature-sputtered TiO_<i>x</i> and C₇₀ acceptor fullerene molecules. We show that defect states in the band gap of TiO_<i>x</i> are quenched by C₇₀ while an interfacial state appears. This new interfacial state is expected to support the favorable energy band alignment observed, showing a perfect match of transport levels, and thus barrier-free extraction of charges, making low-temperature-sputtered TiO_<i>x</i> a good candidate for the next generation of organic solar cells.