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A bulk-heterojunction hybrid solar cell based on CdS quantum dots (QDs) as electron acceptor and P3HT as donor was fabricated for the first time. The CdS QDs synthesized by a one-pot method had good crystallinity and stability. The hybrid thin film of CdS-QDs and conjugated polymer was made by simple spin-coating deposition of CdS-QDs/P3HT composite solution on ITO substrates and then treated by bidentate ligand ethanedithiol. Under AM1.5G illumination, the power-conversion efficiency (PCE) of the thiol-treated monolayer film was more than three times higher than that of the untreated device. The hybrid solar cell based on the assembled trilayer blend film with ethanedithiol by a layer-by-layer approach exhibited a further improved PCE of 0.86%, which was sixfold higher than that of the thiol-treated monolayer device. The results can be explained via ethanedithiol effectively displacing the existing stearate ligands on the surface of QDs in situ and connecting nanoparticles by its end function group, shortening the interdot space and thus improving electron transport between the QDs. The morphology of the thiol-treated blend film was briefly investigated. [ABSTRACT FROM AUTHOR]