May 2019

A collaborative research team from Los Alamos National Laboratory, Rice University, Purdue University, Northwestern University, Institut FOTON CNRS UMR 6082 (France) and Argonne National Laboratory has created a number of hybrid perovskite solar cells with a FA_0.7MA_0.25Cs_0.05PBI₃ composition and measured them using a variety of techniques including grazing-incidence wide-angle x-ray scattering (GIWAXS) maps at the X-ray Science Division 8-ID-E x-ray beamline of the APS (an Office of Science user facility at Argonne).

The experimental setup (top left) and the corresponding light-induced lattice expansion effect, which leads to curing defects and relieving of lattice strain (bottom left) and as a result an increase in the open circuit voltage of a solar cell

In most of the cells, the researchers noted a substantial improvement in PCE from 18.5% to 20.5% under continuous light soaking with a 1-sun (100 mW/cm²) source as the lattice structure of the hybrid cells uniformly expanded. This expansion relieved local strains in the bulk material and better aligned the crystal planes, as evidenced by narrowing and uniform shifting of the Bragg peaks toward lower scattering values as seen by GIWAXS. The researchers explain that constant illumination generates electron-hole pairs in the perovskite material, decreasing the distortions of some bonds while elongating others, resulting in a generalized lattice expansion and relaxation. A similar phenomenon was seen with pure MAPbI₃ thin films, suggesting that such lattice expansion under light is common for hybrid perovskite materials.

Researchers at the University of Toronto have designed a method of growing a more stable electron selective layer for perovskite solar cells and tandem solar cells combining crystalline silicon with perovskite.

Perovskite raw materials can be mixed into a liquid in a kind of 'solar ink.' This solar ink could be printed onto glass, plastic or other materials with a relatively simple inkjet printing process. However, in order to generate electricity, electrons excited by solar energy from perovskite cells must be extracted from a layer of quantum dots that is held together by a passivation layer. Some types of quantum dots are known to change their 3D structure even at room temperature, making them transparent and ineffective. This passivation layer is also known to break down at temperatures above 100°C. The team's breakthrough made both quantum dots and perovskites more stable when combined than they are separated and the solar cell combining of Perovskite material and quantum dots achieved 20.1% efficiency.

Researchers at the Hefei Institutes of Physical Science obtained excellent performance of perovskite solar cells (or PSCs) by excimer laser.

Several problem hinder the progress of PSCs. For example, surface defects decrease their performance, and the preparation process of the common ETL of PSCs requires annealing and crystallization at 400 ' 500 °C, which exceeds the temperature that the common flexible substrates can withstand, and restricts the development of flexible PSCs. To address the above problems, scientists introduced excimer laser into the research of perovskite solar cells (PSCs).

Parasitic absorption in transparent electrodes is one of the main roadblocks to enabling power conversion efficiencies (PCEs) for perovskite'based tandem solar cells beyond 30%. To reduce such losses and maximize light coupling, the broadband transparency of such electrodes should be improved, especially at the front of the device.

Erkan Aydin and coworkers from KAUST Photovoltaics Laboratory have recently shown the excellent properties of Zr'doped indium oxide (IZRO) transparent electrodes for such applications, with improved near'infrared (NIR) response compared to conventional tin'doped indium oxide (ITO) electrodes. Optimized IZRO films feature very high electron mobility (up to '77 cm² V'1 s'1), enabling highly infrared transparent films with a very low sheet resistance ('18 Ω ^'1 for annealed 100 nm films). For devices, this translates to a parasitic absorption of only '5% for IZRO within the solar spectrum (250'2500 nm range), to be compared with '10% for commercial ITO.

For the purpose of decarbonizing the energy-mix, which is becoming a priority challenge for European countries among others, European universities, research institutes and industries involved in the development of perovskite technologies have agreed on the creation of a collaborative platform: the EPKI.

This initiative is dedicated to gathering all significant parties working in this field and is pursuing the following objectives:

• Raise the awareness on perovskite based photovoltaics by conveying a common vision through the editing of a common European perovskite whitepaper,
• Support and initiate next generation PV industrial initiatives,
• Facilitate joint-research programs and synergies among universities, institutes and companies.

Researchers from the University of Toledo have reported progress that may push the performance of tandem perovskite solar cells to new levels. Working in collaboration with the U.S. Department of Energy's National Renewable Energy Lab and the University of Colorado, Dr. Yanfa Yan, UToledo professor of physics, envisions that the new high efficiency tandem perovskite solar cell will be ready to debut in full-sized solar panels in the consumer market in the near future.

"We are producing higher-efficiency, lower-cost solar cells that show great promise to help solve the world energy crisis," Yan said. "The meaningful work will help protect our planet for our children and future generations. We have a problem consuming most of the fossil energies right now, and our collaborative team is focused on refining our innovative way to clean up the mess."

Researchers at the Eindhoven University of Technology in the Netherlands have found a way to address the issue of stability in perovskite solar cells by adding a small amount of fluoride during the production process, which was found to increase the stability of such cells.

Fluoride stablizes perovskite solar cells by encouraging the formation of strong hydrogen bonds and ionic bonds on the surface of the perovskite material.

The scientists found the fluoride ions form a protective layer around perovskite crystals, preventing the ill effects of light, heat and moisture. "Our work has improved the stability of perovskite solar cells considerably," said Shuxia Tao, assistant professor at Eindhoven University of Technology's Center for Computational Energy Research. "Our cells maintain 90% of their efficiency after 1,000 hours under extreme light and heat conditions. This is many times as long as traditional perovskite compounds. We achieve an efficiency of 21.3%, which is a very good starting point for further efficiency gains."

Researchers at the University of Bath have applied a waterproof graphite-based coating to a perovskite cell intended to power the production of hydrogen underwater. The cell reportedly worked underwater longer than expected, and may open the door to a cheap and sustainable way of making hydrogen fuel from water using sunlight.

'The coated cells worked underwater for 30 hours ' ten hours longer than the previous record,' the scientists wrote, adding the glue sandwiching the coat to the cells began to fail after 30 hours. They believe stronger glue could help the cell stabilize for longer. 'We achieve a record stability of 30h in aqueous electrolyte under constant simulated solar illumination, with currents above 2'mA'cm'2 (milliamperes per cm'2) at 1.23'VRHE,' they added.

In December 2018, Greatcell Solar declared bankruptcy, a sad ending to a once promising perovskite venture. However, prior to this bankruptcy (in September 2018), the Production Division of Greatcell Solar was sold off, in a new business called Greatcell Solar Materials (GSM).

GSM manufactures and supplies its products like perovskite precursors, silver inks, various dopants and more to the scientific community. The company's general manager, Dr. Yanek Hebting, kindly agreed to answer some of our questions regarding GSM's business and technology.

Researchers at the National Tsing Hua University in Taiwan, led by Professor Hao-Wu Lin, have demonstrated that high-performance filter-less artificial human photoreceptors can be realized by integrating a novel optical metal/dielectric/metal microcavity structure with vacuum-deposited perovskite photoresponse devices.

Sensory substitution with flexible electronics is one of the intriguing fields of research. Scientists already fabricate electronic devices that can replicate, to a certain degree degree, some of the human senses ' touch (electronic skin ' e-skin), smell (e-nose), and taste (e-tongue). E-versions of the eye's photoreceptors (e-retinas) could potentially be used in a wide range of applications from robotic humanoid vision to artificial retina implantation for vision restoration or even vision extension into a wider range of wavelength.