Perovskites and graphene
Perovskites are materials that share a crystal structure similar to the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3).
Depending on which atoms/molecules are used in the structure, perovskites can possess an impressive array of interesting properties including superconductivity, ferroelectricity, charge ordering, spin dependent transport and much more. Perovskites therefore hold exciting opportunities for physicists, chemists and material scientists.
Graphene is a one-atom-thick layer of carbon atoms arranged in a hexagonal lattice. It is the building-block of Graphite (which is used, among others things, in pencil tips), but graphene is a remarkable substance on its own - with a multitude of astonishing properties which repeatedly earn it the title “wonder material”. Graphene is the thinnest material known to man at one atom thick, and also incredibly strong - about 200 times stronger than steel. On top of that, graphene is an excellent conductor of heat and electricity and has interesting light absorption abilities. These varied properties make it a promising and highly researched material, with hopes of incorporating it in many applications: from inks and composite materials, through sensors, solar cells and water filters, to batteries and supercapacitors.
Due to their unique properties, carbon-based nanomaterials have been the center of extensive research efforts in various fields, one of which is the field of photovoltaic energy conversion. In recent years, hybrid metalorganic halide perovskites have become one of the most promising materials for third generation solar cells, with efficiencies that are constantly on the rise.
The incorporation of graphene into perovskite-based solar cells was naturally proposed, and significant work is taking place on this matter. Graphene-based perovskite solar cells are studied in many ways, including hole and electron transport media (HTM and ETM), electrodes, and various approaches aiming at improving the stability of the device. Tandem architectures based on graphene interlayers are also of great interest.
In addition to solar cells, other areas of graphene and perovskite integration include sensors and photodetectors, QDs, nanocatalysts and more.
Novel graphene-based encapsulation opens door to robust perovskite solar cells
Researchers at Pusan National University, Gwangju Institute of Science and Technology and the Korea Institute of Machinery & Materials (KIMM) in South Korea have tackled perovskite solar cells' stability issues by designing a graphene-based encapsulation technique.
The team introduced a highly flexible and stable graphene encapsulant by adopting the dry transfer method based on a roll-based process.
Graphene boosts perovskite single crystal photodetector performance
The performance of photodetectors based on perovskite polycrystalline thin films is still considered to be at a distance from expected values. One reason is that the carrier transport at the interface is easily affected by grain boundaries and grain defects. Many research groups have tried to combine perovskite polycrystalline thin films with high-mobility, two-dimensional materials to improve device performance, and have achieved promising results, but the negative effects of perovskite polycrystalline grain boundaries still remain.
To solve this problem, a team led by Assoc. Prof. Yu Weili from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, and Prof. GUO Chunlei from the University of Rochester synthesized a low-surface-defect-density CH3NH3PbBr3 microplate through the inverse temperature crystallization strategy. They prepared an effective vertical structure photodetector combining a high-quality perovskite single crystal with monolayer graphene with high carrier mobility.
Graphene "shield" improves the stability of perovskite solar cells
A UNIST research team has developed an electrode that can significantly improve the stability of perovskite solar cells. UNIST announced that its research team developed 'flexible and transparent metal electrode-based perovskite solar cells with a graphene interlayer'.
The team suppressed interdiffusion and degradation using a graphene material with high impermeability, the team said. Team leader professor Hyesung Park commented that the research will greatly help not only solar cells but other perovskite-based flexible photoelectric devices such as LEDs and smart sensors.
Perovskite/graphene nanosensor detects nitrogen dioxide with 300% improved sensitivity
A research team led by Juan Casanova and Eduard Llobet from the Departamento de IngenierÃa Electrónica, Eléctrica y Automática at the Universitat Politècnica de València (URV), used graphene and perovskites to create a nanosensor that detects nitrogen dioxide with 300% improved sensitivity.
The team used graphene that is hydrophobic (water and moisture-resistant) and sensitive in gas detection, but with some limitations: it is not very selective and its sensitivity declines over time. In addition, the researchers used perovskites, a crystalline-structure material commonly used in the field of solar cells. However, they quickly deteriorate when they are exposed to the atmosphere. That's the reason why the team decided to combine perovskites with a hydrophobic material able to repel water molecules - in order to prove they can prevent or slow down their deterioration.
Italian research team develops graphene-enhanced tandem perovskite cell with 26.3% efficiency
Italian researchers from two Italian institutions claim to have developed a two-terminal tandem perovskite-silicon solar cell with a conversion efficiency 26.3%.
The researchers added graphene to the titanium dioxide electron selective layer used in a perovskite solar cell to increase chemical stability. The two-terminal cell was made by stacking two sub-cells which were fabricated and optimized separately. The new device blends the advantages of thin-film perovskite and silicon-based heterojunction cells, according to its developers.
Researchers use perovskite QDs to design a device that mimics brain cells used for human vision
University of Central Florida researchers are helping to close the gap separating human and machine minds, using a technology based on perovskite quantum dots. In a recent study, a UCF research team showed that by combining two promising nanomaterials into a new superstructure, they could create a nanoscale device that mimics the neural pathways of brain cells used for human vision.
"This is a baby step toward developing neuromorphic computers, which are computer processors that can simultaneously process and memorize information," said Jayan Thomas, an associate professor in UCF's NanoScience Technology Center and Department of Materials Science and Engineering. "This can reduce the processing time as well as the energy required for processing. At some time in the future, this invention may help to make robots that can think like humans."
Korean scientists develop graphene electrode to enable next-gen perovskite solar cells
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.
Researchers improved the stability of PSCs using hybrids of graphene and molybdenum disulphide quantum dots
Researchers from the Graphene Flagship have managed to increase the stability of perovskite solar cells (PSCs) using hybrids of graphene and molybdenum disulphide quantum dots.
The team used molybdenum disulphide quantum dot/graphene hybrids to address PSCs' instability issue. The collaboration between research institutions and industrial partners enabled by Graphene Flagship, yielded an ink based on graphene and related materials (GRMs). Layering this over the PSCs caused them to drastically increase in stability.
Emberion team design perovskite-QDs that combine with graphene to create unique photodetectors
Emberion researchers have shown that colloidal quantum dots (QDs) combined with a graphene charge transducer can provide a photoconducting platform with high quantum efficiency and large intrinsic gain, yet compatible with cost-efficient polymer substrates. The team demonstrated methods to couple large QDs (>6 nm in diameter) with organometal halide perovskites, enabling hybrid graphene photo-transistor arrays on plastic foils.
The resulting arrays simultaneously exhibited a specific detectivity of 5 Ã 1012 Jones and high video-frame-rate performance. PbI2 and CH3NH3I co-mediated ligand exchange in PbS QDs improved surface passivation and facilitated electronic transport, yielding faster charge recovery, whereas PbS QDs embedded into a CH3NH3PbI3 matrix produce spatially separated photocarriers leading to large gain.
Graphene to increase efficiency of perovskite solar cells
Researchers from Italy's University of Florence have found that graphene could significantly improve the efficiency of perovskite solar cells. The researchers have shown how the introduction of graphene and graphene oxide doped with lithium atoms (GO-Li) into a perovskite-based cell may increase its conversion efficiency, as both the carrier recombination dynamics and the defect density of the perovskite are considerably improved.
The scientists used graphene doped mesoporous TiO2 (G+mTiO2) with the addition of a lithium-neutralized graphene oxide (GO-Li) interlayer as ETL. They found that the carrier collection efficiency is increased by about a factor two with respect to standard mTiO2.
