Transparency - Page 4

Researchers at the Massachusetts Institute of Technology (MIT) have improved a transparent and conductive coating material by increasing its electrical conductivity by 10 times. When this coating material was integrated into a perovskite solar cell, it boosted the stability and efficiency of the solar cell.

'The goal is to find a material that is electrically conductive as well as transparent,' explained the team, which would be ‘'useful in a range of applications, including touch screens and solar cells.'

A research group led by Prof. Liu Shengzhong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) and Prof. Yang Dong at Shaanxi Normal University have developed high efficiency semi-transparent perovskite solar cells by using MoO₃ sandwiched gold nanomesh (MoO₃/Au/MoO₃) multilayer as the transparent electrode. Combined with a superior heterojunction silicon solar cell, a high efficiency four-terminal perovskite/silicon tandem solar cell was obtained.

Tandem/multijunction structure has been proven to be an effective way to break the Shockley-Queisser limit. To obtain a high efficiency tandem solar cell, the key is to fabricate transparent electrode with high conductivity as well as high transparency through a mild method.

Researchers from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia and University of Twente in the Netherlands have developed transparent conductive films that let through a broader range of the solar spectrum, which are set to increase the power conversion efficiency of perovskite-based multijunction solar cells beyond 30%.

A comparison of the used device test structures with different silicon bottom cells. Image taken from Advanced Functional Materials

Performance of perovskite-based tandem solar cells rests on the ability of the top cell to harvest the blue portion of the solar spectrum while letting through the near-infrared light. Conversely, the bottom cell only needs to absorb near-infrared light. "The semitransparency of the top cell depends on the optical bandgap and thickness of the perovskite thin film as well as the characteristics of the transparent electrodes, especially their sun-exposed side," explains study lead Stefaan De Wolf from theKAUST Solar Center.

MIT researchers have designed perovskite photovoltaic-powered sensors that could potentially transmit data for years before they need to be replaced. To this end, the team mounted thin-film perovskite cells as energy-harvesters on inexpensive radio-frequency identification (RFID) tags.

The cells could power the sensors in both bright sunlight and dimmer indoor conditions. Moreover, the team found the solar power actually gives the sensors a major power boost that enables greater data-transmission distances and the ability to integrate multiple sensors onto a single RFID tag.

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.