Efficiency - Page 56

An international team of researchers led by the University of Cambridge found that a simple potassium solution could boost the efficiency of perovskite-based solar cells, by enabling them to convert more sunlight into electricity. The addition of potassium iodide seems to have a 'healing' effect on the defects and immobilized ion movement, which to date have limited the efficiency of perovskite solar cells.

Tiny defects in the crystalline structure of perovskites, called traps, can cause electrons to get 'stuck' before their energy can be harnessed. The easier it is for electrons to move around in a solar cell material, the more efficient that material will be at converting photons into electricity. Another issue is that ions can move around in the solar cell when illuminated, which can cause a change in the bandgap ' the color of light the material absorbs.

The recent Silicon PV/nPV conference in Lausanne, Switzerland, saw Solliance's announcement on the achievement of a major milestone in perovskite technology for application in future industrial high efficiency tandem photovoltaic cells and modules. Solliance announced realizing a perovskite cell that combines good cell efficiency with a very high near infrared transparency of 93%.

Also at the conference, ECN shows that when this perovskite cell is mechanically stacked on a 6 inch² silicon bottom cell with its proprietary MWT-SHJ (metal-wrap-through silicon heterojunction) design, 26.3% efficiency is achieved, an increase of 3.6% points over the efficiency of the directly illuminated silicon cell laminate.

Researchers at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have gained new understanding of the happenings inside a hybrid perovskite material in the first few trillionths of a second after it's hit with simulated sunlight.

The blue and green spheres are atoms. When light hits, electrons start to separate from positively charged 'holes,' the first step in creating an electrical current (yellow streaks). Meanwhile, atoms begin to vibrate within the perovskite's structure.

The research, conducted at the atomic scale, could help explain how electric charges move efficiently through hybrid perovskites following the absorption of light, the crucial first step in generating an electric current. The study used laser pulses that match the intensity of solar radiation, and thus mimic natural sunlight. The authors say their discovery could lead to improvements in the performance of perovskite solar cells and a new way to probe their functionality.

In a work supported by the Department of Energy (DOE) and Office of Science, Basic Energy Sciences (BES), researchers from Stanford, University Pennsylvania, SLAC National Accelerator Lab, Columbia University, Carnegie Institute for Science in Washington and Weizmann Institute of Science in Israel, have shown how atoms in perovskites respond to light and could explain the high efficiency of these perovskite-based solar cells.

The team explains that sunlight causes large changes to the underlying network of atoms that make up perovskites. Before being hit with light, six iodine atoms rest around a lead atom. Within 10 trillionths of a second after being hit with light, the iodine atoms whirl around each lead atom. These first atomic steps distort the structure and result in significant changes. Furthermore, the atoms' motions alters the way electricity flows and may help explain the efficiency of perovskites in solar cells.

New research by teams at Inha University and Chonnam National University in South Korea reveals how to improve the lifetime of perovskite-based solar cells. The team has developed a method known as co-precipitation to make a thin film comprising nanoporous nickel oxide as the hole transporting layer (HTL) for a perovskite solar cell that uses the unique composition of FAPbI3 and or MAPbBr3 as the perovskite layer. In addition, they used an organic air-stable inorganic zinc oxide nanoparticles compound as the ETL (electron transporting layer) in order to protect the perovskite layer from air.

"We successfully optimized the metal oxide based HTL and ETL protecting layers for highly efficient perovskite absorber by a simple method which can make air-stable photovoltaics," explains co-author of the study. "Our main goal is to solve the problem of the tedious process of making conventional additive-doped, highly expensive, unstable HTLs by replacing low-cost, inorganic air-stable p and n-type metal oxides," he added.

CHEOPS, a European research project with a focus on upscaling perovskite photovoltaic cells, has released a new research that shows a way to reduce the 'dead area' of photovoltaic cells by applying an enhanced laser patterning process. This new development means that more of the area of a cell can be used for energy conversion, making it more efficient.

For upscaling efforts to achieve suitable currents, photovoltaic cells are usually split into a series of interconnected segments. It is these breaks in the material that need to be made as small as possible to be able to optimize the cell for energy conversion. This so-called 'dead area' has been reduced to a width of 400μm by using a new laser patterning process.

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.

Researchers from Germany's research center Helmholtz Zentrum Berlin (HZB) have found the reason why holes in perovskite films produced through a spin coating technique and used in solar cells do not cause a reduction in the cells' performance.

The team said that these holes, which are commonly responsible for leading to short circuits in the solar cell by the adjacent layers of the solar cell coming into contact, if produced through a spin coating technique, do not lead to significant short circuits between the front and back contact of the cell, and so do not negatively impact the cell's performance.

Researchers at the University of Groningen are working on a special type of solar cell that is made of organic-inorganic hybrid perovskites. The team has been focusing on a material in which hot electrons retain their high energy levels for much longer, which might make it possible to use more of their energy to obtain a higher voltage.

Most hybrid-perovskite solar cells contain lead, which is toxic. The research group recently published a paper describing 9% efficiency in a hybrid-perovskite solar cell containing tin instead of lead. "When we studied this material further, we observed something strange", the team said. The results showed that the hot electrons produced in the tin-based solar cells took about a thousand times longer than usual to dissipate their excess energy.