Technical / research - Page 11

Researchers at Rice University, along with researchers from several institutions in the U.S. and abroad, including Lawrence Berkeley National Laboratory; University of California, San Diego; University of Lille, National Center for Scientific Research (CNRS), Centrale Lille Institut; University of Artois; Northwestern University; Purdue University; University of Rennes, INSA Rennes, CNRS, Institut FOTON; Brookhaven National Laboratory; University of Washington; and Northwestern University, have described a way to synthesize formamidinium lead iodide (FAPbI₃) ⎯ the type of crystal currently used to make the highest-efficiency perovskite solar cells ⎯ into ultrastable, high-quality photovoltaic films. The overall efficiency of the resulting FAPbI₃ solar cells decreased by less than 3% over more than 1,000 hours of operation at temperatures of 85 degrees Celsius (185 Fahrenheit).

“Right now, we think that this is state of the art in terms of stability,” said Rice engineer Aditya Mohite, whose lab has achieved various improvements in perovskites’ durability and performance over the past several years. “Perovskite solar cells have the potential to revolutionize energy production, but achieving long-duration stability has been a significant challenge.”

Researchers at China's Shanghai University, Southern University of Science and Technology, The University of Hong Kong, Yunnan University, Beijing Institute of Technology and Japan's Yamagata University have developed a stable, efficient and high-color purity hybrid light-emitting diodes (LEDs) with a tandem structure, by combining perovskite LED and commercial organic LED technologies. 

Device structure. Image credit: Light: Science & Applications

Perovskite-based LED technology can have tunable emission wavelength in visible light range as well as narrow linewidth, which makes it a promising contender among current light-emitting display technologies. However, it still suffers from severe instability driven by electric field. The research team in this work set out to tackle this challenge, by developing a method to create efficient and stable hybrid perovskite-organic light-emitting diodes.

Researchers in China, led by Nanjing University, have designed a tandem perovskite-silicon solar cell with a top perovskite device based on an absorber treated with n-butanol (nBA), which reportedly reduces the detrimental effects of moisture in manufacturing processes carried out in air environment. The resulting PV device is said to have improved charge collection.

The nBA used by the team is a clear, colorless alcohol used as a cleaning agent in many industries, including electronics manufacturing. The team explained that it offers low polarity and saturation vapor pressure and ensures that the typical detrimental effects of moisture in perovskite cell fabrication in an ambient environment can be significantly reduced.

MIT researchers have developed a new computer vision technique that significantly speeds up the characterization of newly synthesized electronic materials. The technique automatically analyzes images of printed semiconducting samples and quickly estimates two key electronic properties for each sample: band gap and stability.

Overview of the synthesis and characterization pipeline for perovskite semiconductors. Image credit: Nature Communications

The new technique reportedly characterizes electronic materials 85 times faster compared to the standard benchmark approach. The researchers intend to use the technique to speed up the search for promising solar cell materials. They also plan to incorporate the technique into a fully automated materials screening system.

Researchers from Australia's Monash University and CSIRO Manufacturing have reported a lamination technique, known as cold isostatic pressing (CIP), to build a perovskite solar cell based on a flexible bilayer electrode made of carbon and silver. The resulting electrode can reportedly compete with gold-carbon electrode based counterparts in terms of efficiency and stability.

The back side of a C-PSC with a custom-designed electrode after CIP processing. Image credit: Communications Materials

The researchers, led by CSIRO Manufacturing, which is part of Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO), explained that while perovskite solar cells (PSCs) with evaporated gold (Au) electrodes have shown promising efficiencies, the maturity of the technology still demands low-cost and scalable alternatives to progress towards commercialization. Carbon electrode-based PSCs (C-PSCs) represent a promising alternative, however, optimizing the interface between the hole transport layer (HTL) and the carbon electrode without damaging the underlying functional layers is a persistent challenge, which the team set out to address.

Researchers from the University of North Carolina at Chapel Hill, Colorado School of Mines, National Renewable Energy Laboratory (NREL), University of Toledo and University of California San Diego have pointed out that the light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would encounter in actual outdoor use. 

The scientists reported degradation mechanisms of p-i-n–structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) reportedly dominate the accelerated A-site cation migration, rather than direct degradation of HTMs.

Researchers from the Ningbo Institute of Materials Technology and Engineering at the Chinese Academy of Sciences recently reported a novel perovskite/silicon tandem solar cell based on flexible ultrathin silicon, with a thickness of about 30 µm.

Despite major progress in the efficiency of rigid perovskite/silicon tandem solar cells, flexible perovskite/silicon tandem solar cells have remained elusive. The team explains that this is due to the challenge of enhancing light absorption in ultrathin silicon bottom cells while maintaining their mechanical flexibility.

Researchers at China's Hangzhou Dianzi University have modified the absorber of a conventional perovskite solar cell with potassium trifluoromethanesulfonate (KTFS) and found that the additive improved the device's performance and stability. The cell’s perovskite film reportedly showed less lead defects and lower J-V hysteresis.

“The KTFS molecule is a typical kind of potassium salt including the cationic potassium (K⁺) and anionic trifluoromethanesulfonate (SO3CF3−), indicating a bifunctional interaction between KTFS and perovskite,” the team explained. “The sulfonyl group can passivate the undercoordinated lead of the deep-level defect and thus inhibit the non-radiative recombination.”

Researchers from Purdue University and ShanghaiTech University have developed a patent-pending method to synthesize high-quality, layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions.

The novel method creates layered perovskite nanowires with exceptionally well-defined and flexible cavities that exhibit a wide range of unusual optical properties beyond conventional perovskites.

Researchers at City University of Hong Kong (CityU) have presented a novel material design strategy and simple device-manufacturing process for skin-conformable perovskite-based alternating-current electroluminescent (PeACEL) devices. 

Working mechanism of the PeACEL device. Image credit: Nature Photonics

These devices exhibit a narrow emission bandwidth (full-width at half-maximum, <37 nm), continuously tunable emission wavelength (468–694 nm), high stretchability (400%) and adequate luminance (>200 cd m−2).