NREL - Page 6

Researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have reported the development of an environmentally-stable perovskite solar cell that reportedly maintained 94% of its starting efficiency after 1,000 hours of continuous use under ambient conditions.

'During testing, we intentionally stress the cells somewhat harder than real-world applications in an effort to speed up the aging,' says an involved researcher at NREL. 'A solar cell in the field only operates when the sun is out, typically. In this case, even after 1,000 straight hours of testing the cell was able to generate power the whole time.'

Scientists at the Department of Energy's National Renewable Energy Laboratory (NREL) and at the University of Texas at Austin have conducted the first quantitative nanoscale photoconductivity imaging of two perovskite thin films with different power conversion efficiencies.

The team's microscopic analysis of perovskite solar cells reveals new insight into how the devices degrade'information necessary for improving their performance and moving the technology closer to commercialization.

A team at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have developed a novel perovskites and CNTs-based demonstration device that responds to sunlight by transforming from transparent to tinted while converting sunlight into electricity.

A switchable photovoltaic window

The thermochromic windows technology responds to heat, as was said, by transforming from transparent to tinted. As the window darkens, it generates electricity. The color change is driven by molecules (methylamine) that are reversibly absorbed into the device. When solar energy heats up the device, the molecules are driven out, and the device is darkened. When the sun is not shining, the device is cooled back down, and the molecules re-absorb into the window device, which again appears transparent.

Researchers at the National Renewable Energy Laboratory (NREL) and the University of Washington have designed an interesting strategy for driving down the cost of solar cells while ramping up efficiency: the team developed a high cost, high efficiency quantum dot solar cell for space applications, and provided the expensive solar cell up with a cheaper perovskite layer. The combined solar cell would be aimed at terrestrial applications with a more moderate price point. Note that in the proposed lower cost solar cell, the cheap layer is not the only role for perovskite. The expensive quantum dot layer would also be made of perovskite.

The NREL team explains that colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties. That first quantum dot solar cell had a conversion efficiency of just 2.9% and was based on a lead sulfide formula. Things moved along quickly after that, and NREL noted a record of 12% for lead sulfide achieved by the University of Toronto just last year.

Researchers affiliated with UNIST, the Korea Institute of Chemical Technology (KRICT) and Hanyang University have designed a cost-efficient method to produce inorganic-organic hybrid perovskite solar cells (PSCs), with outstanding efficiency performance of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

A key feature of this technology is its ability to tackle the dominating defect in perovskite-halides, which is known to decrease the photoelectric efficiency. The team's results demonstrate that careful control of the growth conditions of perovskite layers with management of deficient halide anions is essential for realizing high-efficiency thin-film PSCs based on lead-halide-perovskite absorbers.

Researchers at the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) developed a new perovskite ink with a long processing window that allows the scalable production of perovskite solar cells.

To create a perovskite film, a coating of chemicals is deposited on a substrate and heated to fully crystalize the material. The various steps involved often overlap with each other and complicate the process. One extremely critical stage requires the addition of an antisolvent that extracts the precursor chemicals, and thus create crystals of good quality. The window for this step opens and closes within seconds, which is detrimental for manufacturing due to the precision required to make this time window. NREL researchers were able to keep that window open as long as 8 minutes.

Researchers from the Energy Department's National Renewable Energy Laboratory (NREL) have found that surface recombination limits the performance of polycrystalline perovskite solar cells. In such cells, the sunlight creates mobile electrons whose movement generates power, but upon encountering defects can slip into a non-productive process. Known as a recombination, this process reduces the efficiency of a solar cell.

The NREL team examined the surface recombination in lead iodide perovskites, and determined that recombination in other parts of a methylammonium perovskite film is less important than processes that are happening on the surface, both the top and bottom. The team explained that multiple sources of recombination exist, and that surfaces are often overlooked when paying attention to recombination in favor of grain boundaries and bulk defects.

Researchers from the US National Renewable Energy Laboratory (NREL) have achieved 10.77% conversion efficiency with perovskite solar cells made from quantum dots with no organic components.

Solutions of all-inorganic perovskite quantum dots, showing intense photoluminescence when illuminated with UV light

The result was achieved with a thin film made of nanocrystals of cesium lead iodide (CsPbI3). The team discovered a method to keep the crystal structure in the all-inorganic perovskite material stable at room temperature, something that was previously possible only at temperatures exceeding 600 degrees Fahrenheit. The use of methyl acetate as an anti-solvent to remove excess unreacted precursors proved a crucial step in increasing the nanocrystals' stability.

Researchers at the Energy Department's National Renewable Energy Laboratory (NREL) discovered a use for perovskites that could push forward the development of quantum computing.

The discovery, made quite accidentally, occurred while the researchers were investigating excitons in perovskites. The sample was illuminated with a short laser pulse whose wavelength was specifically tuned to avoid being absorbed by the sample. Instead, the exposure triggered a strong interaction of light with the perovskite, producing a shifted transition energy known as the optical Stark effect. The effect occurs in semiconductors, but typically can only be observed at extremely low temperatures in very high-quality, high-cost materials. NREL's scientists were able to observe the effect quite readily at room temperature in materials grown using solution processing.

Scientists at the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL), in collaboration with researchers at Shanghai Jiao Tong University (SJTU), have reportedly devised a method to improve perovskite-based solar cells, making them more efficient and reliable with higher reproducibility.

The research was funded by the DOE's SunShot Initiative. It involved hybrid halide perovskite solar cells and revealed treating them with a specific solution of methyl ammonium bromide (MABr) would repair defects, improving efficiency. The scientists converted a low-quality perovskite film with pinholes and small grains into a high-quality film without pinholes and with large grains. This apparently boosted the efficiency of the perovskite film in converting sunlight to 19%, according to NREL.