SAN FRANCISCO Carrier multiplication, a phenomenon in which semiconductor nanocrystals respond to photons by producing multiple electrons, is applicable to a broader array of materials than previously thought, according to scientists at Los Alamos National Laboratory.
According to the scientists, the discovery increases the potential for the use of nanocrystals as solar cell materials to produce higher electrical outputs than current solar cells.
In a statement issued by Los Alamos Wednesday (Jan. 4), the laboratory asserts that in papers published recently in the journals Nature Physics and Applied Physics Letters, the scientists demonstrate that carrier multiplication is not unique to lead selenide nanocrystals, but also occurs with very high efficiency in nanocrystals of other compositions, such as cadmium selenide.
The scientists' new results shed light on the mechanism for carrier multiplication, which likely occurs via the instantaneous photoexcitation of multiple electrons, Los Alamos said. Such a process has never been observed in macroscopic materials and it explicitly relies on the unique physics of the nanoscale size regime, according to Los Alamos, which is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy.
"Our research of carrier multiplication in previous years was really focused on analyzing the response of lead selenide nanocrystals to very short laser pulses," said Richard Schaller, a Los Alamos scientist on the team, in a statement. "We discovered that the absorption of a single photon could produce two or even three excited electrons. We knew, somewhat instinctively, that carrier multiplication was probably not confined to lead selenide, but we needed to pursue the question."
Los Alamos said the findings point toward practical photovoltaic technologies that may utilize such traditional solar cell materials as cadmium telluride, which is very similar to cadmium selenide. Other interesting opportunities may also be associated with the use of carrier multiplication in solar-fuel technologies and specifically, the production of hydrogen by photo-catalytic water splitting, according to the laboratory.
In addition to Schaller, the Los Alamos team that made the discovery includes Lead project scientist Victor Klimov and Melissa Petruska. All three team members are from Los Alamos' Physical Chemistry and Applied Spectroscopy group.
More information on Los Alamos quantum dot research is available on the organization's Web site.