Several research institutions in South Korea are actively conducting research and development on next-generation solar cells, heightening expectations for commercialization. The research team led by Prof. Yoon Soon-gil of Chungnam National University has developed a new graphene electrode to produce perovskite solar cells at a low temperature. In addition, the team led by Prof. Choi Kyoung-jin of the School of Materials Science and Engineering at UNIST has developed a new concept tandem solar cell using transparent conductive adhesives (TCA).

The graphene electrode developed by Professor Yoon's team can help create a perovskite solar cell at a low temperature and can raise both safety and economic efficiency.

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.

A joint research team including scientists from the Chinese Academy of Scinces (CAS), Shijiazhuang Tiedao University in China and Chiao Tung University in Taiwan has developed a novel type of highly flexible and stable perovskite-based solar cell that could be used in wearable electronics.

The team stated that current PSCs are mainly made of a polymer substrate, which has been proven fragile, unstable and not adequately waterproof. The team built a new type of PSC based on an inorganic mica substrate, which could reduce the strain in the device even under large bending deformation. Mica is a mineral that separates easily into small flat transparent pieces of rock.

Researchers at Solliance, in collaboration with MiaSole Hi-Tech Corp., have designed a flexible solar cell with an impressive power conversion efficiency of 21.5%. The solar cell combines two thin-film solar cell technologies into a 4 terminal tandem solar cell stack: a top flexible semi-transparent perovskite solar cell with a bottom flexible copper indium gallium selenide (CIGS) cell.

A tandem solar cell, which combines a perovskite and a Cu(In,Ga)Se2 (CIGS) cell, has the potential for high conversion efficiency exceeding single junction solar cell performance thanks to tunable and complementary bandgaps of these individual thin film solar cells. CIGS technology has a proven track record as a high efficiency and stable solar technology, and has entered high volume manufacturing in multi-GW scale around the world. CIGS technology has been successfully used to produce high efficiency flexible and lightweight cells and modules, which address markets where heavy and rigid panels cannot be used. Perovskite solar cells, promise low cost solar technology based on abundant materials. Combining both technologies in a flexible and lightweight package expands the horizon of high performance, flexible, and customizable solar technology.

Researchers from the Ulsan National Institute of Science and Technology (UNIST) have developed perovskite LEDs (PeLED) which are flexible enough to be folded. A transparent material was used in the electrode of the device as a replacement for metal to ensure translucency.

Flexible translucent PeLED maintains performance even when bending curvature is small

According to the team, PeLED is a kind of light emitting diode (LED) that emits light by injecting current into a compound. This device uses a perovskite material as an active layer that emits light by receiving electricity, and its advantages include high electron mobility, good color purity, and easy color control. However, conventional PeLEDs are low in flexibility and opaque due to limitations of metal electrodes.

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 The University of Tokyo's Institute of Industrial Science (IIS) have made advancements in the design of transparent solar materials. These could be suitable for roof-mounted solar panels or ones that are placed on windows. Instead of silicon, the cell is based on a perovskite material. A thin perovskite layer absorbs sunlight to generate an electric charge, which is transmitted to an electrode layer sandwiched between perovskite and a glass backing.

A major challenge in the field of solar panels is to create a material that absorbs enough light to produce power, yet still manages to remain transparent. To achieve this, the IIS researchers exploited the properties of the human eye. They took account of the fact that, for visual purposes, not all colors are equal. In fact, the eye is much more sensitive to green light, in the middle of the spectrum, than red or blue. According to the rules of "human luminosity," a good supply of green light is the main priority for visibility. Their new material was therefore designed to mostly absorb red and blue light, while letting green through.

A research team at the Korea Advanced Institute of Science and Technology (KAIST) and Sungkyunkwan University developed a perovskite-based solar cell that is semi-transparent, highly efficient and functions very effectively as a thermal-mirror.

The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells.

Researchers at Pennsylvania State University have developed a transparent and electrically conductive material that could make large screen displays, smart windows, touch screens and solar cells more affordable and efficient. The material has the potential to replace indium tin oxide (ITO), the transparent conductor that is currently used for more than 90% of the display market but is expensive, scarce and brittle.

Along with display technologies, the researchers will investigate the new materials with a type of solar cell that uses organic perovskite materials. The team has reported a design strategy using 10 nm-thick films of an unusual class of materials called correlated metals. In most conventional metals, such as copper, gold, aluminum or silver, electrons flow like a gas. In correlated metals, such as strontium vanadate (a perovskite material) and calcium vanadate, they move more like a liquid. The electron flow produces high optical transparency along with high metal-like conductivity, the researchers said.

Researchers involved in the €10.6 million European research project called GRAFOL have reportedly demonstrated a cost-effective roll-to-roll production tool capable of making large sheets of graphene on an industrial scale, which could greatly contribute to flexible thin-film solar cells with transparent electrodes like perovskite PVs.