Abstract: Disclosed is a quantum dot based solar cell device which includes a substrate, a light harvesting structure sandwiched between electrically conducing layers, with at least one electrically conducting layer being substantially transparent with the light harvesting structure being located on the substrate. The light harvesting structure includes a layer of semiconducting quantum dots, with this layer of semiconducting quantum dots including at least two distinct sets of semiconducting quantum dots which are homogenously mixed. One of the two distinct sets of semiconducting quantum dots has a first bandgap and the at least one other distinct set of semiconducting quantum dots has a second bandgap different from the first bandgap. Both sets of semiconducting quantum dots are passivated with any one or combination of halides and pseudo-halides.