Improving solar cell efficiency with upconversion nanoparticles
An international research team has developed a multiband near-infrared (NIR) upconversion (UC) system to enhance light harvesting in silicon solar cells (SSCs). The system is based on the idea of lanthanide-doped upconversion nanoparticles (UCNPs), which convert low-energy photons in the infrared range into higher-energy photons in visible light.
“We have developed an efficient approach for collecting more of the NIR energy in sunlight by SSCs by integrating multiband NIR responsive core-shell UCNPs,” explained the team, noting that it consists of multilayer nanoparticles containing lanthanide (Lb) and ytterbium (Yb), which can capture NIR energy in a broad range of 1,100 to 2,200 nm.
The system also contains holmium ion (Ho³⁺), erbium ion (Er³⁺), and thulium ion (Tm³⁺), which are all Ln activator ions. Using a solvothermal method, they were all synthesized to create core-shell-shell-shell (CSSS) nanocrystals. Yb³ was introduced to all layers of the CSSS, and the team found it to “serve as a highly efficient electron pump, in synergistic action with the long-wavelength excitation NIR light, and simultaneously acts as a two-photon UC emitter.”
After creating this CSSS UCNP, the team vertically placed commercial solar cells measuring 150 mm x 150 mm into it and then placed the whole device in an oven at 30 C for four hours. The resultant CSSS films were relatively flat, with a low roughness of 6.19 nm. Different film thicknesses were produced, ranging from 130 nm to 550 nm.
“In comparison to the uncoated SSCs with an absolute photon conversion efficiency of 18.5% achieved, the efficiency of the SSCs coated with a CSSS film of 182 nm was increased to 19.37% (a net increase of 0.87%),” the academics said “The increase of efficiency for SSCs is dominated by the short-circuit currents. Further increasing the film thicknesses, the efficiency gradually decreases.”
Concluding their article, the researchers added that the optimized multilayer Ln/Yb-UCNPs exhibit a broad multiband NIR response distributed across the range from 1,100 to 2.200 nm, with an aggregated bandwidth of approximately 500 nm. “This design achieves an overall UC photoluminescence quantum yield (PLQY) of 12% under standard solar irradiation,” they stated.
They also added that the CSSS-coated cell proved durable, maintaining functionality for more than 55,100 hours under standard temperature and humidity conditions. “Those results make them highly valuable for practical applications,” the scientists added.
Their findings were presented in “A multiband NIR upconversion core-shell design for enhanced light harvesting of silicon solar cells,” published in Light: Science & Applications. Scientists from China’s Jilin University, Dalian Minzu University, and Sweeden’s KTH Royal Institute of Technology have conducted the study.
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