Researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory have demonstrated that the effectiveness of solar cells can be improved by coating the nanoparticles used in their construction with an organic dye, which greatly enhances their ability to capture infrared light.

The team members published their results in the journal Nature Photonics, describing how they were able to reengineer the dye-coated nanoparticles to improve their light-converting efficiency by around 100 times. The dye itself was found to amplify the brightness of reemitted light by around 33,000-fold.

“These organic dyes capture broad swaths of near-infrared light,” said Bruce Cohen, a scientist at Berkeley Lab’s Molecular Foundry and co-lead author of the study.

“Since the near-infrared wavelengths of light are often unused in solar technologies that focus on visible light, and these dye-sensitised nanoparticles efficiently convert near-infrared light to visible light, they raise the possibility of capturing a good portion of the solar spectrum that otherwise goes to waste, and integrating it into existing solar technologies,” he said.

Additional experiments by UC Berkeley PhD student David Garfield and Molecular Foundry scientist Nicholas Borys showed a symbiotic relationship between the dye and the lanthanide metals which compose part of the nanoparticles. The proximity of the dye to the metals enhanced the presence of a state ducked a ‘triplet’, which causes energy to be transferred to the metals more efficiently.

The triplet state enabled the conversion of multiple infrared photons into single photons of visible light, and was shown to be even more effective when the concentration of lanthanide metals in the nanoparticles was increased from 22% to 52%.

“The metals are promoting dyes to their triplet states, which helps to explain both the efficiency of energy transfer and the instability of the dyes, since triplets tend to degrade in air,” said Cohen.

While the nanoparticles are currently unstable–the experiments were conducted in a nitrogen environment to avoid exposure to air–the dyed nanoparticles could be used to improve the efficiency of solar cells, or introduced into cells to label cells for microscopy studies, making them useful for deep-tissue imaging.