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‘Deforming’ solar cells could be clue to improved efficiency

‘Deforming’ solar cells could be clue to improved efficiency

  • Deformations and defects in structures of photoelectric technologies shown to improve their efficiency
  • University of Warwick physicists demonstrate that strain gradient can prevent recombination of photo-excited carriers in solar energy conversion
  • Increasingly important as devices become miniaturised

Solar panelsSolar cells and light-sensing technologies could be made more efficient by taking advantage of an unusual property due to deformations and defects in their structures.

Researchers from the University of Warwick’s Department of Physics have found that the strain gradient (i.e. inhomogeneous strain) in the solar cells, through physical force or induced during the fabrication process, can prevent photo-excited carriers from recombining, leading to an enhanced solar energy conversion efficiency. The results of their experiments have been published in Nature Communications.

The team of scientists used an epitaxial thin film of BiFeO3 grown on LaAlO3 substrate to determine the impact of inhomogenous deformation on the film’s ability to convert light into electricity by examining how its strain gradient affects its ability to separate photo-excited carriers.

Most commercial solar cells are formed of two layers creating at their boundary a junction between two kinds of semiconductors, p-type with positive charge carriers (electron vacancies) and n-type with negative charge carriers (electrons). When light is absorbed, the junction of the two semiconductors sustains an internal field splitting the photo-excited carriers in opposite directions, generating a current and voltage across the junction. Without such junctions the energy cannot be harvested and the photo-excited carriers will simply quickly recombine eliminating any electrical charge.

They found that the strain gradient can help prevent recombination by separating the light-excited electron-holes, enhancing the conversion efficiency of the solar cells. The BiFeO3/LaAlO3 film also exhibited some interesting photoelectric effects, such as persistent photoconductivity (improved electrical conductivity). It has potential applications in UV light sensors, actuators and transducers.

Dr Mingmin Yang from the University of Warwick said: “This work demonstrated the critical role of the strain gradient in mediating local photoelectric properties, which is largely overlooked previously. By engineering photoelectric technologies to take advantage of strain gradient, we may potentially increase the conversion efficiency of solar cells and enhance the sensitivity of light sensors.

“Another factor to consider is the grain boundaries in polycrystalline solar cells. Generally, defects accumulate at the grain boundaries, which would induce photo-carrier recombination, limiting efficiency. However, in some polycrystalline solar cells, such as CdTe solar cells, the grain boundaries would promote the collection of photo-carriers, where the giant strain gradient might play an important role. Therefore, we need to pay attention to the local strain gradient when we study the structure-properties relations in solar cells and light sensor materials.”

Previously, the effect of this strain on efficiency was thought to be negligible. With the increasing miniaturisation of technologies, the effect of strain gradient becomes magnified at smaller sizes. So in reducing the size of a device using one of these films, the magnitude of strain gradient increases dramatically.

Dr Yang adds: “The strain gradient induced effect, such as flexo-photovoltaic effect, ionic migration, etc, would be increasingly important at low dimensions.”

Materials provided by University of Warwick

solar panels array

Scientists develop new material for improving efficiency of solar panels

Clean energy acts as an intersection which acts as a suitable substitution for fossil fuels. It is noticed that solar power plants have to boost their planning in a better way to compete with the electrical output of the non-renewable energy sources. The design highly depends upon the renovation and growth of newly made products such that they ingest and interchange the heat at the higher temperatures.

 The solar panels which are found on the hybrid cars or the residential rooftops are found lesser compared to the ones found in the solar power plants. Since the solar panels found in the power plants are huge and countless in number so the heat they absorb is more so they absorb more thermal energy from the sun as much as they can and then they create a passage so that the heat can pass through and that heat is converted into fluid-filled converter is known as heat exchanger.

A liquid version of carbon dioxide which is known as supercritical CO2 acts as an agency in converting the energy and the hotter the fluid gets the more the electricity can be produced. Researchers from the University of Toledo have discovered a newer technology based on the supercritical CO2 as a channel which helps in converting into energy and here this fluid minimizes the manufacturing costs and also minimizes the electricity level and commits to working in a good manner with accuracy and it can benefit to the future power plants too. This report was published in Nature journal

An assistant professor in the mechanical engineering department at Texas A&M University Dorrin Jarrahbashi said that the metal material which is used to make the solar panel heat exchangers using supercritical CO2 energy cycles are only firm up to 550 degrees Celsius and he also added that if the heat rises then break down occurs which leads to the replacement of the components and becomes less effective.

To solve this problem the researchers developed a new complex material which had a combination of ceramic and tungsten which is refractory metal which can take the heat of over 750 degrees Celsius. The tendency to tolerate heat can lead to more effectiveness in generating electricity in united solar and supercritical CO2 power plants by 20%. Compared to the fossil fuels the output and the longevity of the mixture and the lower cost in production will help in cutting down the price of construction and maintenance of powerplants.

It is said that with the help of the unique chemical, mechanical and thermal properties there is numerous approach for the compound. It started from improving its nuclear power plants to building rocket nozzles the results of this revolution has made a vast impact in the future of research and industry.

Mohave Generating Station

Scientists demonstrate generation of electricity from coldness of universe

Conventional resources of energy have been providing and powering our needs since electricity was made in the late 1800s. The conventional resources of energy are polluting as well as a temporary solution for providing electricity. They are going to get over in the next couple of years after which we humans have to look out and seek other alternative resources, in the recent decade we have seen a good rise in the dependency on renewable sources of energy as we found out ways to develop electricity from water, wind, thermal and pressure differences.

Solar panels are currently the sector in boom however there are disadvantages to it. The drawbacks are that it cannot produce electricity in the absence of sunlight. Many regions of the Earth have a frigid zone where the chilling outflow can be harvested using thermal differences using the same kind of physics we use for solar panels. Scientists have demonstrated a way to generate a measurable amount of electricity, directly from the coldness of the universe. The semiconductor device faces the infrared rays of the sun and uses temperature difference of the Earth and the space to produce electricity.

In optoelectronic physics, there is a vast symmetry between incoming and outgoing radiations. In comparison to the leveraging energy (incoming), the negative illumination effect allows electricity to be harvested as the heat is transferred. The technology today is unable to capture the negative temperature difference very efficiently. The temperature in space is absolute zero and thus devices can be used to generate electricity.

The group found that negative illumination diode has the ability to generate 64 nanowatts of electricity per square meter,  this is very less than the theoretical standard. However Dr.Mashashi Ono, the author on this paper published in Applied Physics Letters, said that through increasing the optoelectronic efficiency and the material used, the power generated per square meter can be increased hugely. But when calculations are made and when atmospheric factors are taken into consideration we see that it has the ability to generate a power of 4 watts per square feet theoretically, which is enough to run power machinery during night time.

A typical solar panel can, however, produce close to 100-200 watts per square feet. Shanhui Fan, an author of a similar paper said that same principle could be used to recover waste heat from machines. From now onwards, however, he and his group are focusing on increasing the efficiency of the panels which if succeeds will be a breakthrough for mankind in its thirst to develop non-conventional resources of energy. Fan also comments that the vastness of the universe is a thermodynamic resource.