Silicon-based solar panels currently on the market are unable to convert all radiations on the electromagnetic spectrum, such as infrared, which has a relatively long wavelength, so the panels’ energy conversion efficiency tops out at 30%. In response to this, researchers at KTH Royal Institute of Technology have developed a new type of solar cell design by applying a thin film over existing solar cells, which can increase their energy conversion rate by an estimated 25%. Their findings are published in the scientific journal Nanoscale.
Sunlight encompasses lights of several different wavelengths, from ultraviolet rays with comparatively shorter wavelengths to infrared light with longer wavelengths. The wavelength of an electromagnetic radiation is inversely proportional to its photon energy. Solar panels generate electrical energy by absorbing photons in the sunlight into its conduction bands. However, if the gap between these bands are larger than photons, then the photon energies can slip through, and no electricity is generated as a result. That is why solar panels cannot absorb all radiations on the electromagnetic spectrum.
Solar panels on the market today can absorb near-infrared lights, visible lights, and ultraviolet lights, but not infrareds, which have longer wavelengths, thus missing out on nearly 44% of all radiations. The radiations that slip through band gaps are converted into heat, which is both wasteful and detrimental to the efficiency of solar panels.
Scientists have been hard at work to address this problem, including a research team from KTH, who sought to create simple solutions while maximizing results. One solution entails the creation of a thin film made from nanoparticles dyed with lanthanide and other metal ions and then mixed with microlenses. This film is capable of transforming infrared light into electricity.
The nanoparticles involved are known as upconverting nanoparticles (UNCP). Multiple photons with long wavelengths are absorbed by metal-organic compounds or other semiconductor-based nanomaterials, which then release them as shorter-wavelength lights. One example of this process in action is the conversion of infrared light into visible light.
The U.S.-based Lawrence Berkeley National Laboratory previously performed a similar procedure by coating particles with organic dye, which can capture infrared light, and then converting infrared into visible light. More recently, researchers at Florida State University captured infrared with lead-halide perovskites and reemitted upconverted visible light with rubrene, a type of hydrocarbon.
The KTH research team’s solution involves layering a polymer-based film over the surface of solar cells to absorb and spatially modulate infrared light. This process has the advantage of boosting the energy conversion efficiency of solar cells. “The ability of the microlenses to concentrate light allows the nanoparticles to convert the weak IR light radiation to visible light useful for solar cells,” according to Hans Ågren, professor in theoretical chemistry at KTH.
KTH’s researchers claim that they have achieved a 10% increase in energy conversion efficiency without optimizing the technology. They estimate that a further 20% to 25% increase in efficiency can be achieved in the future. Citing possible room for improvement, the team is hopeful that UNCP has the potential to emit more infrared light by minimizing the current iteration’s inefficiencies.