Peak External Photocurrent Quantum Efficiency Exceeding 100% via MEG in a Quantum Dot Solar Cell

• Published in: Science (American Association for the Advancement of Science) Vol. 334; no. 6062; pp. 1530 - 1533
• Main Authors: Semonin, Octavi E., Luther, Joseph M., Choi, Sukgeun, Chen, Hsiang-Yu, Gao, Jianbo, Nozik, Arthur J., Beard, Matthew C.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 16.12.2011; The American Association for the Advancement of Science
• Subjects: Applied sciences; Charge carriers; Electric current; Energy; Energy gaps; Exact sciences and technology; Excitons; Hydrazines; Material films; Materials science; Narrative devices; Natural energy; Photocurrent; Photoelectric effect; Photons; Photovoltaic cells; Photovoltaic conversion; Quantum dots; Quantum efficiency; Semiconductors; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Solar cell; Exciton; Semiconductor quantum dots; Quantum dot; Charge carrier; Internal reflection; Electron hole pair; Light absorption; Photon absorption; Quantum yield; Photoelectric current; Nanocrystal
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1209845

Multiple exciton generation (MEG) is a process that can occur in semiconductor nanocrystals, or quantum dots (QDs), whereby absorption of a photon bearing at least twice the bandgap energy produces two or more electron-hole pairs. Here, we report on photocurrent enhancement arising from MEG in lead selenide (PbSe) QD-based solar cells, as manifested by an external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) that peaked at 114 ± 1% in the best device measured. The associated internal quantum efficiency (corrected for reflection and absorption losses) was 130%. We compare our results with transient absorption measurements of MEG in isolated PbSe QDs and find reasonable agreement. Our findings demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.