Plasmonic Schottky Nanojunctions for Tailoring the Photogeneration Profile in Thin Film Solar Cells

Schottky nanojunctions are presented, fabricated from solution-processed PbS quantum dot films and self-assembled Ag nanoparticle arrays. If the Ag nanoparticle arrays are sufficiently dense to ensure the overlap of the individual depletion regions set up around the discrete Ag nanoparticles, open circuit voltages and shunt resistances similar to reference Schottky junctions with bulk Ag contacts can be achieved. Light is incident from the Ag nanoparticle side of the device and can excite localized surface plasmon resonances in the metal. These plasmonic resonances strongly concentrate the electromagnetic field within tens of nanometers of the nanoparticles. The resulting absorption profile is modified such that carriers are generated close to the metal-semiconductor interface, within the depletion region of the Schottky diodes. In this way, the generation profile is tailored across the device to achieve more efficient carrier collection. External quantum efficiency spectra exhibit clear spectral features characteristic of near-field assisted absorption, as predicted by full field optical simulations. By comparing two different active layer thicknesses-resulting in one depleted reference device and one partially depleted-it is possible to differentiate between the optical (due to changes in absorption) and electrical (due to changes in carrier collection efficiency) effects of modifying the generation profile in Schottky diodes.