American researchers have devised a method to effectively ‘reshape’ the solar spectrum by boosting low-energy infrared photons to make them capable of generating power inside photovoltaic cells.
The technique, described in the latest issue of the journal Nano Letters, could improve efficiency of existing solar cells by more than 30 per cent.
"The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today's solar cells," said Christopher Bardeen, a Professor of chemistry at the University of California.
"This is energy lost, no matter how good your solar cell.”
To reduce the amount of the ‘wasted’ light, the researchers created a mixture of inorganic semiconductor crystals and organic molecules that could be used to coat conventional silicon-based solar panels.
In experiments, this mixture proved capable of capturing infrared photons and combining their energies into one higher-energy particle.
“The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon,” explained Bardeen. “This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted."
In lab experiments, the researchers directed 980-nanometer infrared light at the hybrid material, which then generated upconverted orange/yellow fluorescent 550-nanometer light, almost doubling the energy of the incoming photons.
"This 550-nanometer light can be absorbed by any solar cell material," Bardeen said. "The key to this research is the hybrid composite material - combining inorganic semiconductor nanoparticles with organic compounds. Organic compounds cannot absorb in the infrared but are good at combining two lower energy photons to a higher energy photon. By using a hybrid material, the inorganic component absorbs two photons and passes their energy on to the organic component for combination. The organic compounds then produce one high-energy photon. Put simply, the inorganics in the composite material take light in; the organics get light out."
Besides solar energy, the ability to upconvert two low energy photons into one high energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes.