New Nanostructured Materials for Efficient Photon Upconversion

• Published in: IEEE journal of photovoltaics Vol. 5; no. 1; pp. 224 - 228
• Main Authors: Sellers, Diane G., Polly, Stephen J., Yujun Zhong, Hubbard, Seth M., Zide, Joshua M. O., Doty, Matthew F.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01-01-2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Absorption; Bandgap engineering; dilute bismuthides; Gallium arsenide; InAs quantum dots (QDs); Lighting; Nanostructured materials; Photoconductivity; Photonic band gap; Photonics; Photovoltaic cells; Quantum dots; Solar energy; upconversion; Bandgap engineering; upconversion; InAs quantum dots (QDs); dilute bismuthides
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2014.2367865

Although methods for harvesting subbandgap solar photons have been demonstrated, present approaches still face substantial challenges. We evaluate carrier escape mechanisms in an InAs/GaAs quantum dot (QD) intermediate band photovoltaic (PV) device using photocurrent measurements under subbandgap illumination. We show that subbandgap photons can generate photocurrent through a two-photon absorption process, but that carrier trapping and retrapping limit the overall photocurrent regardless of whether the dominant carrier escape mechanism is optical, tunneling, or thermal. We introduce a new design for an InAs QD-based nanostructured material that can efficiently upconvert two low-energy photons into one high-energy photon. Efficiency is enhanced by intentionally sacrificing a small amount of photon energy to minimize radiative and nonradiative loss. Upconversion PV devices based on this approach separate the absorption of subbandgap photons from the current-harvesting junction, circumventing the carrier-trapping problems.