Quantum dot solar cell with quantum dot bandgap gradients

Efficient photovoltaic devices with quantum dots are provided. Quantum dots have numerous desirable properties that can be used in solar cells, including an easily selected bandgap and Fermi level. In particular, the size and composition of a quantum dot can determine its bandgap and Fermi level. By precise deposition of quantum dots in the active layer of a solar cell, bandgap gradients can be present for efficient sunlight absorption, exciton dissociation, and charge transport. Mismatching Fermi levels are also present between adjacent quantum dots, allowing for built-in electric fields to form and aid in charge transport and the prevention of exciton recombination.