Introducing plasmonic resonant scatterers in photovoltaic devices is a promising way to increase energy conversion efficiencies by trapping incoming light in ultra-thin solar cells. Colloidal nanogap antennas are obtained following a cost-effective self-assembly strategy and incorporated in organic-based cells produced using spin-coating techniques in ambient air conditions. We report an interesting increase of both external quantum efficiency (EQE) and short circuit current for solar cells loaded with plasmonic oligomers compared with reference organic cells with and without isolated gold nanoparticle. Theoretical calculations demonstrate that the wavelength dependent EQE enhancement is a resonant process due to the increased scattering efficiency in plasmonic antennas allowed by a chemically controlled 1 nm nanogap. This method opens the way towards roll-to-roll fabrication of efficient plasmonic ultra-thin photovoltaic devices.