Recent leapfrogging of power conversion efficiencies of quantum dot solar cells (QDSCs) have catapulted them to the forefront of low cost photovoltaic cells. Here, bimetallic Au−Ag (3:1) alloy nanoparticles (NPs) are embedded in a TiO2/CdS film to yield a TiO2/CdS/Au−Ag (3:1) film. Charge carriers in the QDSC with the TiO2/CdS/Au−Ag (3:1) film upon illumination are produced via three distinctive mechanisms: inherent electron-hole pairs formed in CdS, e−-h+ pairs formed in CdS by the absorption of the increased electric field halo around the vicinal alloy NPs, and by the excitation of electrons to mid-gap states of CdS by absorption of longer wavelengths scattered by the alloy NPs. The high electrical conductivity of Au−Ag (3:1) alloy NPs facilitates electron transport in the TiO2/CdS/Au−Ag (3:1) film and the Fermi level shift to more negative potentials (versus normal hydrogen electrode) induced by the alloy, increases photovoltage and suppresses electron recombination. The champion plasmonic QDSC with the TiO2/CdS/Au−Ag (3:1) film delivered a PCE of 4.94 %, which is greater by 52 % compared to the non-plasmonic cell. The plasmonic cell exhibits enhanced external quantum efficiencies (EQEs) in the blue-green region, and the EQE is finite in the red region as well. We expect that the findings for improved energy harvesting induced by Au−Ag (3:1) alloy NPs in this work will furnish useful design ideas for developing plasmonic cells with a variety of other QDs. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim