Efficiency - Page 57

EPFL researchers have shown that Incorporating guanidinium into perovskite solar cells stabilizes their efficiency at 19% for 1000 hours under full-sunlight testing conditions.

A major challenge in the PSCs field is stability; Unlike silicon cells, perovskites are soft crystalline materials and prone to problems due to decomposition over time. In a commercial context, this tends to inflate the costs of perovskite-based solar cells compared with conventional silicon cells. There have therefore been many efforts in synthesizing perovskite materials that can maintain high efficiency over time. This is done by introducing different cations (positively charged ions) into the crystal structure of the perovskite. Although success has been reported in several studies, these solutions can often be difficult and expensive to implement.

A team at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have developed a novel perovskites and CNTs-based demonstration device that responds to sunlight by transforming from transparent to tinted while converting sunlight into electricity.

A switchable photovoltaic window

The thermochromic windows technology responds to heat, as was said, by transforming from transparent to tinted. As the window darkens, it generates electricity. The color change is driven by molecules (methylamine) that are reversibly absorbed into the device. When solar energy heats up the device, the molecules are driven out, and the device is darkened. When the sun is not shining, the device is cooled back down, and the molecules re-absorb into the window device, which again appears transparent.

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 team of researchers, that includes researchers from the AMOLF Institute in the Netherlands and Argonne National Laboratory and is led by the University of California San Diego, has observed nanoscale changes in hybrid perovskite crystals that could offer new insights into developing low-cost, high-efficiency solar cells.

Using X-ray beams and lasers, the researchers studied how hybrid perovskites behave at the nanoscale level during operation. Their experiments revealed that when voltage is applied, ions migrate within the material, creating regions that are no longer as efficient at converting light to electricity. "Ion migration hurts the performance of the light absorbing material. Limiting it could be a key to improving the quality of these solar cells," said a member of the Sustainable Power and Energy Center at UC San Diego.

Solliance has achieved a new world record for Perovskite Solar Cell technology demonstrated on industrially applicable Roll-to-Roll (R2R) processes of 13.5% conversion efficiency at cell level. The group stressed that the records were achieved in a factory setting, using an industrially scalable process.

Solliance has achieved the conversion efficiency of 13.5% and module-level aperture area conversion efficiency of 12.2% for perovskite-based photovoltaics using industrially-applicable, roll-to-roll production processes. By further optimizing and re-validating processes that were earlier developed buy Solliance, the performance at both the cell and module level have been improved.

A research team from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw and the Ecole Polytechnique Federale de Lausanne (EPFL) in Lausanne (Switzerland), co-operating within the GOTSolar project, has demonstrated a perovskite solar cell with a significantly smaller number of structural defects. The unexpected improvement of the photovoltaic performance was observed when perovskites produced by mechanochemistry were used for the construction of a typical photovoltaic cell.

The group from IPC PAS (Warsaw University of Technology) was the first to demonstrate that polycrystalline halide perovskites (CH3NH3)PbI3 can be produced in mechanochemical reactions. Recently, the group presented the mechanochemical production of mixed perovskites, those in which several different types of ions alternate in position A. This is an important achievement, because by carefully altering the chemical composition of the perovskite materials, they can be adapted to specific applications in photovoltaics, catalysis and other fields of science and technology.

Researchers at the National Renewable Energy Laboratory (NREL) and the University of Washington have designed an interesting strategy for driving down the cost of solar cells while ramping up efficiency: the team developed a high cost, high efficiency quantum dot solar cell for space applications, and provided the expensive solar cell up with a cheaper perovskite layer. The combined solar cell would be aimed at terrestrial applications with a more moderate price point. Note that in the proposed lower cost solar cell, the cheap layer is not the only role for perovskite. The expensive quantum dot layer would also be made of perovskite.

The NREL team explains that colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties. That first quantum dot solar cell had a conversion efficiency of just 2.9% and was based on a lead sulfide formula. Things moved along quickly after that, and NREL noted a record of 12% for lead sulfide achieved by the University of Toronto just last year.

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.

Researchers from Lomonosov Moscow State University in Russia explained how changing the ratio of components forming the light-absorbing layer of a perovskite solar cell influences the structure of created films and battery efficiency.

Perovskites can be used to create perovskite solar batteries, which are a relatively new area of R&D, but are showing promise in terms of efficiency and function. In their previous work, the researchers found out that filiform (wire-like) hybrids of perovskites have acquired their shape because of the structure of intermediate compounds, which are formed during the process of perovskite crystallization. The team has discovered a whole group of these compounds, every one of which is a crystalline solvate. The crystalline solvates are crystalline compounds with the molecules of the precursor components' solvent built into their structure. The dissolved components precipitate from the solution and form a crystalline film of perovskite.

A team of researchers from The Hebrew University of Jerusalem in Israel, led by Prof. Lioz Etgar, investigated the optical and physical properties of bromide quasi 2D perovskites synthesized using different barrier molecules. The team reports on the high power conversion efficiency (PCE) and high open circuit voltage (V_oc) of bromide-based quasi 2D perovskite solar cells.

The various bromide quasi 2D perovskites were introduced into two PV cell configurations (with and without HTM). The use of the quasi 2D perovskite as an absorbing layer in PSCs reportedly yields improved efficiencies and open circuit voltage as compared to 3D PSCs. Different barriers in the quasi 2D structures have been shown to affect the photovoltaic performance; the cells' performance is reduced when increasing barrier length. However, the perovskite's hydrophilic character is suppressed with an increase in the chain length of the barrier molecule.