Researchers have developed a new material that is capable of generating electricity from otherwise wasted infrared photons thereby increasing the efficiency of currently used solar photovoltaic cells by at least 30 per cent.
One of the major hurdles in installation of solar cells is the cost – nearly 80 per cent of the costs comes from space for the solar cells (open land) and labour. Though solar energy is cheap, the need for open space takes a toll on the overall cost of the project, which eventually deters prospects who are looking to opt for this means of energy.
Researchers have been looking for options using which they can either alleviate the need for open space or come up with a solution that makes solar cells more efficient. In a step towards making solar cells more efficient, researchers have come up with a new material that is capable of converting infrared light from the sun to electricity. Currently, infrared photons normally pass right through the solar cells without being converted to electricity.
A team of chemists at the University of California, Riverside reveal through their paper in in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in “upconverting” photons in the visible and near-infrared regions of the solar spectrum and convert them to electricity.
Christopher Bardeen, a professor of chemistry and Ming Lee Tang, an assistant professor of chemistry explain in the paper that the light in the infrared region is the energy lost because it is not absorbed by currently used solar cells, no matter how good they are.
Researchers added that the new hybrid material they have managed to develop is the first of its kind capable of capturing two infrared photons and adds their energies together to make one higher energy photon. This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted.
The scientist peg this particular mechanism as “reshaping the solar spectrum” that make the light match the need of photovoltaic materials used today in solar cells. The ability to utilize the infrared portion of the solar spectrum could boost solar photovoltaic efficiencies by 30 percent or more.
For their new material, Bardeen and Tang worked with cadmium selenide and lead selenide semiconductor nanocrystals. The organic compounds they used to prepare the hybrids were diphenylanthracene and rubrene. The cadmium selenide nanocrystals could convert visible wavelengths to ultraviolet photons, while the lead selenide nanocrystals could convert near-infrared photons to visible photons.
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. The researchers were able to boost the upconversion process by up to three orders of magnitude by coating the cadmium selenide nanocrystals with organic ligands, providing a route to higher efficiencies.
“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. Bardeen emphasized that the research could have wide-ranging implications.
“The ability to move light energy from one wavelength to another, more useful region, for example, from red to blue, can impact any technology that involves photons as inputs or outputs,” he said.
