Bright future for polymer-based solar cells

SOLAR energy and solar photovoltaic (PV) in particular has got many advantages. Solar energy is completely pollution- and noise-free and produces no waste such as carbon dioxide, chemical pollutants, or even nuclear waste. Moreover, this type of energy source doesn’t require water that it has minimal impact on the environment. It is size independent; unlike conventional power plants (coal, gas, nuclear,) or even CSP (concentrated solar power) it can be used in 1kW domestic applications or street lights, as well as in multi-hundred megawatt utility scale applications. This allows solar PV to be the most versatile source of energy that can be installed with the right capacity in the shortest possible time anywhere, where energy is needed. Solar energy generators also require much less maintenance compared to conventional generators.

Solar PV is a very established technology. Some manufacturers – like SOLON – have got production and installation experience for close to 20 years. Mr. Sascha Gaede, Director Global Sales at Solon International FZE said that United Arab Emirates as of now is using negligible percentage of energy  through solar but this is going to change with the latest announcement by Dubai Electricity and Water Authority (DEWA) which is setting up a 100MWp PV plant 30kms south of Dubai.

SOLON is a manufacturer of high performance PV Solar cells and innovative solar modules, having produced 1.4 gigawatt (GW) of solar systems, including supply of more than 450 megawatt peak (MWp) small and large scale turnkey power plants on roof, as well as greenfield worldwide. SOLON is represented with facilities in Europe, America and Asia with its group's largest manufacturing capacities in Fujairah, UAE.

Mr. Gaeda said that solar energy is produced majorly in two plants in the UAE as of now; one 10MWp plant owned and operated by Masdar in Abu Dhabi and one 13MWp plant owned and operated by DEWA in Dubai. Both plants combined would be producing 2.5 million units (kWhs) per month (estimates and not actual data). He added that there are further discussions about allowing private solar-systems to be grid-connected and the governments to promote industrial rooftop programs. The capital of Abu Dhabi announced its plan to produce 7% of its energy through solar by 2020 and Dubai announced to produce 5% of its energy requirement by 2030. In the wider region, many projects are slated for implementing renewable energies, as well.

Mr. Sascha Gaeda, Director Global Sales, Solon International FZE

Cost consideration

Today, the focus remains on the cost of the solar panels and the materials and technology deployed. Amongst all the different technologies, polymer solar cells offer better services and opportunities. These cells generally contain benign and environmental friendly materials which can be made flexible and lightweight. The challenge remains improvising their power conversion efficiency. A recent study by Professor Tobin J. Marks of Northwestern University reports the design and synthesis of new semi-conductors and fill-factors of 80%, close to that of silicon solar cells. The fill factor achieved is more than 10% greater than previously achieved by the polymer solar cell community, and, in the present study, although the polymer semiconductors have non-optimal light absorption characteristics, near-record power-conversion efficiency as high as 8.7% is still obtained.

"Our results indicate that the power-conversion efficiency achievable with polymer solar cells may be far beyond the current levels, heralding a bright future for this technology," Prof. Marks said. "With our high fill factors, polymers with very good but not champion light absorption are still able to achieve very good efficiency."

Polymer-based solar cells have two domains, consisting of an electron acceptor and an electron donor material. Excitons are the energy particles created by solar cells when light is absorbed. In order to be harnessed effectively as an energy source, excitons must be able to travel quickly to the interface of the donor and acceptor domains and retain as much of the light’s energy as possible.

Researchers have suggested that one way to  increase polymer solar cell efficiency is to adjust the difference between the highest occupied molecular orbit (HOMO) of the acceptor and lowest unoccupied molecular orbit (LUMO) levels of the polymer so that the exciton can be harvested with minimal loss. One of the most common ways to accomplish this is by adding a fluorine atom to the polymer’s molecular backbone, a difficult, multi-step process that can increase the solar cell’s performance, but has considerable material fabrication costs.

 

The many advantages of polymer solar cells

Polymer solar cells generally hold multiple advantages such as they are lightweight, possibly disposable, flexible, customizable on the molecular level and inexpensive to fabricate not to mention that they have lower negative environmental impact.

It is imperative to remember that whilst discussing solar cell efficiency, it is best to compare solar cells that are similar in design as there are a lot of different types of solar cells that vary greatly in cost, complexity, mechanical properties and other parameters. Factors like price per kilowatt or purpose applicability should be a primary consideration. Secondly, research and commercial solar cells are different as research cells may be quite efficient but difficult or virtually impossible to produce on a commercial basis.

Mr. Gaeda confirmed that in the commercial manufacture of modules, there is no high-performance plastics used as such, but Solon uses a variety of polymer based solutions for creating the insulation sheets that are on the back of the modules. Plastics, nonetheless, are used by Solon in the construction of a substructure for an innovative product line called SOLfixx, based on the principle of non-grouted mounting for flat roofs. Materials such as PVF (polyvinyl fluoride) and PET are amongst the polymer solutions used in the company’s solar panels.

Generally, it is seen that most commercial solar cells are made from a refined purified silicon crystal crystal, similar to materials used for the manufacture of integrated circults and computer chips.

Since a lot of research & development activities are currently focusing on new applications, plastics could play an important role in supplying light and climate resistant substructures for roofs or facades. Last year, Masdar Institute of Science and Technology, an independent, research-driven graduate-level university focused on advanced energy and sustainable technologies in the capital of Abu Dhabi, announced its researchers fabricated the very first bulk-hetero-junction solar cell in the UAE, marking a technological breakthrough for the country in clean energy.

This renders the potential limitless. Gaeda confirmed that done centrally, meaning with big solar farms, a few 100 sqkm patches in each of the emirates within the UAE, will be able to generate the entire daytime electricity requirement for the given emirate even if it is as big as Dubai as each 100 sqkm patch can practically produce 5GW worth of energy. If de-centralised, on private or industrial rooftops, a similar coverage could be used.

Mr. Gaeda also listed challenges for solar energy and its growth to progress such as political and regulatory issues and right political frameworks that allow PV solar systems to be installed and systems to be connected to the grid. Grid-connection allows surplus solar-energy to be fed into the grid during the day, and to be taken out again during the night (Net-Metering). The grid would function as a virtual battery, allowing Solar PV to play a much bigger role in the everyday supply of electricity. sneakers