Benefiting from the strong quantum confinement, PbSe nanocrystals allow their bandgap and absorption edge to be tuned to optimize the absorption of the solar radiation. Here, bandgap engineering-based photovoltaic devices were designed, fabricated, and characterized using two-size PbSe nanocrystals. The fabricated two size particle photovoltaic devices showed 12.8% higher power conversion efficiency compared to that of the single-particle devices, as a result of the enhanced photon absorption and the improved charge transfer.