Scientists, at New Mexico-based Los Alamos National Laboratory (LANL), have developed the technology that could potentially turn any window into a power source. For the very first time, researchers have managed to build large-scale luminescent solar concentrators (LSCs) that, unlike their predecessors, are colorless, non-toxic and incredibly efficient. A type of building-integrated photovoltaic material, the device uses colloidal quantum dots (basically, semiconductor nanocrystals) for the concentration and absorption of incident solar radiation.
The study, entitled “Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots”, was conducted by Los Alamos scientists, in collaboration with Italy-based University of Milan-Bicocca (UNIMIB). Recently published in the Nature Nanotechnology journal, it represents a fundamental advancement in the available LSC technology. Speaking about the new research, Victor Klimov, a scientist at LANL’s Center for Advanced Solar Photophysics (CASP) and the study’s lead author, said:
In these devices, a fraction of light transmitted through the window is absorbed by nanosized particles (semiconductor quantum dots) dispersed in a glass window, re-emitted at the infrared wavelength invisible to the human eye, and wave-guided to a solar cell at the edge of the window. Using this design, a nearly transparent window becomes an electrical generator, one that can power your room’s air conditioner on a hot day or a heater on a cold one.
Previous varities were only a few centimeters in size, and were based on less-efficient organic emitters, that in turn absorbed only a fraction of the incident sunlight. Furthermore, such concentrators used quantum dots derived from toxic heavy metals, like cadmium, which, along with their strong reddish yellow coloring, made them wholly unsuitable for use in residential environments. The new research marks the first time that scientists have developed large-scale luminescent solar concentrators, with high light-harvesting efficiency and zero re-absorption losses while transmitting the collected luminescence. Kilmov added:
Our new devices use quantum dots of a complex composition which includes copper (Cu), indium (In), selenium (Se) and sulfur (S). This composition is often abbreviated as CISeS. Importantly, these particles do not contain any toxic metals that are typically present in previously demonstrated LSCs… Furthermore, the CISeS quantum dots provide a uniform coverage of the solar spectrum, thus adding only a neutral tint to a window without introducing any distortion to perceived colors. In addition, their near-infrared emission is invisible to a human eye, but at the same time is ideally suited for most common solar cells based on silicon.
In the research, the team has also developed a technique, similar to the cell casting method, by which high optical quality polymer windows can be easily turned into quantum dot-based solar windows. It involves the embedding of non-toxic quantum dots in a transparent polymer matrix, particularly a cross-linked polylaurylmethacrylate. The PLMA side chains actually prevent the quantum dots from forming a lump, by providing an environment similar to the collodail suspension. This ensures that the nanoparticles retain their light emission and absorption properties, even when encapsulated inside the polymer. Sergio Brovelli, of UNIMIB, explained:
Quantum dot solar window technology, of which we had demonstrated the feasibility just one year ago, now becomes a reality that can be transferred to the industry in the short to medium term, allowing us to convert not only rooftops, as we do now, but the whole body of urban buildings, including windows, into solar energy generators. This is especially important in densely populated urban area where the rooftop surfaces are too small for collecting all the energy required for the building operations. Add to [this]…, the energy that would be saved by the reduced need for air conditioning thanks to the filtering effect by the LSC, which lowers the heating of indoor spaces by sunlight, and you have a potentially game-changing technology towards ‘net-zero’ energy cities.
According to Brovelli, replacing the approximately 12,000 windows (around 72,000-square-meters) of a skyscraper, like NYC’s One World Trade Center, with a photovoltaic facade, made of quantum dot solar windows, would likely produce sufficient power to meet the energy demands of over 350 apartments. However, the technology is still quite few years away from being commercially viable. Talking about the challenges that need to be overcome, Hunter McDaniel, a former postdoctoral fellow at Los Alamos, said:
…with a new class of low-cost, low-hazard quantum dots composed of CISeS, we have overcome some of the biggest roadblocks to commercial deployment of this technology. One of the remaining problems to tackle is reducing cost, but already this material is significantly less expensive to manufacture than alternative quantum dots used in previous LSC demonstrations.