New eco-friendly quantum dots absorb infrared light and boost solar cell efficiency

Using quantum dots (QDs) as sensitizers in solar cells opened new doors in light harvesting technology, however there are still efforts to find a nontoxic alternative to cadmium-based QDs. Type II Cu₂GeS₃/InP core/shell QDs are potentially efficient sensitizers but have only been used to absorb visible spectrum light. As half of the solar cell is located in the infrared region, Zavaraki et al. designed and synthesized type II Cu₂GeS₃/InP core/shell QDs with a broader absorption bandwidth.

Theoretical calculations from density functional theory revealed promising band alignment and infrared absorption for type II Cu₂GeS₃/InP core/shell QDs solar cells. The authors synthesized single core and type II Cu₂GeS₃ core/shells by one-pot colloidal synthesis using what’s known as the hot injection method. They deposited QDs on the TiO₂ solar substrate for characterization, followed by optimization of QD synthesis and device fabrication.

Spectrophotometer readings showed that the type II core/shell QDs had a high absorption spectrum and red-shifted to higher wavelengths. Under simulated light, the type II core/shell QDs solar cells had five times higher power conversion efficiency than the single core QDs. The authors also used photon to current efficiency measurements to confirm the increased power conversion efficiency, and time-resolved fluorescence lifetime measurements to assess the electron injection rate constant.

The tests discovered that the superior band alignment enabled easy injection of electrons from the conduction band of the core into that of the shell, and finally into the TiO₂ substrate. Another advantage was that the valence band offset between semiconductors in the core and shell effectively separated the charge and repressed recombination. Author Asghar Jamshidi Zavaraki intends to continue to increase solar cell efficiency using other such eco-friendly materials.

Source: “Low toxic Cu₂GeS₃/InP quantum dot sensitized infrared solar cells,” by A. Jamshidi Zavaraki, J. Huang, Y. Ji, and H. Ågren, Journal of Renewable and Sustainable Energy (2018). The article can be accessed at https://doi.org/10.1063/1.5044608 .