Efficiency - Page 44

Research by scientists at the Eindhoven University of Technology and universities in China and the US sheds new light on the causes of the degradation perovskites undergo when exposed to sunlight and paves the way for designing new perovskite compositions for the ultimate stable solar cells.

The new research focuses on perovskite solar cells made from formamidinium-caesium lead iodide, a halide compound that has become increasingly popular as it combines high efficiency and reasonable heat resistance with low manufacturing costs.

A team of researchers at the Nanyang Technological University, Singapore (NTU Singapore) has created a perovskite solar mini module that has reportedly recorded the highest power conversion efficiency of any perovskite-based device larger than 10 cm².

The NTU researchers report that they have adopted a common industrial coating technique called 'thermal co-evaporation' and found that it can fabricate solar cell modules of 21 cm² size with record power conversion efficiencies of 18.1%.

A recent study reported the highest efficiency ever recorded for full roll-to-roll printed perovskite solar cells (PSCs), marking a significant step on the way to cheaper and more efficient ways of generating solar energy.

The team at Swansea University's SPECIFIC Innovation and Knowledge Center, led by Trystan Watson, reported using a roll-to-roll fabrication method for four layers of slot-die coated PSCs. The PSCs gave the stable power output of 12.2 percent - the highest efficiency recorded for four layers of roll-to-roll printed PSCs to date.

Researchers at Cambridge's Department of Materials Science and Metallurgy, working with Imperial College London and the Solar Energy Research Institute of Singapore, have developed a method to print ultrathin coatings on perovskite-based solar cells, allowing them to work in tandem with silicon solar cells to boost efficiencies.

Solar cells work by absorbing sunlight to produce clean electricity. But photovoltaics can absorb only a fraction of the solar spectrum, which limits their efficiencies. The typical efficiency of a solar panel is only 18-20%.

An international research team, led by Stefan Weber from the Max Planck Institute for Polymer Research in Mainz, has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell.

Clever alignment of these electron highways could make perovskite solar cells more efficient. When solar cells convert sunlight into electricity, the electrons of the material inside the cell absorb the energy of the light. The electrons excited by the sunlight are collected by special contacts on the top and bottom of the cell. However, if the electrons remain in the material for too long, they can lose their energy again. To minimize losses, they should therefore reach the contacts as quickly as possible. Microscopically small structures in the perovskites - so-called ferroelastic twin domains - could be helpful in this respect: They can influence how fast the electrons move.

A team of researchers led by Nanchang University in China tested a polymer-based hole transport layer for flexible perovskite solar cells, using a glue to attach it to the active perovskite. The team was able to assemble the cells into a small flexible module suitable for wearable solar applications, and says its design was inspired by the structure and movements of human vertebrae.

Bio-inspired vertebral design for scalable and flexible perovskite solar cells. Image from Nature Communications

The team reported that the solar cell measured 1.01cm² and achieved a stabilized efficiency of 19.87%. The cell was tested for 3000 hours under one-sun illumination at room temperature and was shown to retain 85% of its initial efficiency.

Researchers in Japan's Kyushu University have modified the tin(IV) oxide layer of a perovskite device with a fullerene-derivative-based self-assembled monolayer to produce a cell they claim offers stability and a reduction in the hysteresis effect which makes predicting power output so tricky.

The Kyushu University team has developed a surface treatment method for perovskite cell production they say reduces hysteresis ' an effect which afflicts perovskite devices because their output depends on a variety of previous inputs rather than just their immediate condition, rendering performance less predictable. In perovskite cells, hysteresis is strictly dependent on the composition of the material. Ion migration and non-radiative recombination near interfaces are generally considered responsible for the effect.

Researchers from Nigeria's African University of Science and Technology (AUST), working with scientists from Worcester Polytechnic Institute in the U.S., have suggested a novel fabrication method for perovskite solar cells.

Inspired by previous work on other organic thin-film solar cell materials, the group investigated the effects of pressure on perovskite cell production by using computational analysis and practical experimentation. A previous study at Brown University showed how the correct application of stress could heal cracks in perovskite solar cells but little information is available about how pressure could be applied to production processes.

An international collaboration led by Antonio Abate, HZB, and Zhao-Kui Wang, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, China, has achieved a breakthrough that opens up a path to non-toxic perovskite-based solar cells that provides stable performance over a long period.

They use tin instead of lead but have created a two-dimensional structure by inserting organic groups within the material, which leads to so-called 2D Ruddlesden-Popper phases.

Iowa State University engineers, in a project partially supported by the National Science Foundation, have found a way to take advantage of perovskite's useful properties while stabilizing the cells at high temperatures.

Vikram Dalal, an Iowa State University Professor in Engineering and corresponding author of the paper, said there are two key developments in the new solar cell technology: First, he said the engineers made some tweaks to the makeup of the perovskite material. They got rid of the organic components in the material ' particularly cations, materials with extra protons and a positive charge ' and substituted inorganic materials such as cesium. That made the material stable at higher temperatures.