A review paper by Khalifa University and a team of international scientists advances understanding of the latest developments underway to improve the performance and cost of flexible, polymer solar cells

On the roadmap of the world’s transition to clean energy, solar power leads the way. Every day, the sun releases more energy than humanity needs to power everything on Earth, but tapping into that power remains the challenge. Photovoltaics are electronic devices that convert sunlight into electricity, and while their cost has plummeted recently due to intense interest, challenges remain.

Researchers from Khalifa University have collaborated with a team of international researchers to conduct a review of cathode buffer layers used in organic solar cells. Their review paper, which was published in, explains the advances researchers have made in recent years in materials science to improve the overall efficiency and lifetime of this type of photovoltaic.

Dr. Vinay Gupta and Dr. Shashikant Patole, both Assistant Professors in the Khalifa University Department of Physics, undertook their review in collaboration with researchers from the CSIR-National Physical Laboratory, India, Swansea University, United Kingdom, and the University of Jammu, India.

An organic solar cell is a type of photovoltaic that uses conductive organic polymers to absorb light and produce electricity from sunshine. Most organic photovoltaic cells are polymer solar cells.

Compared to silicon-based devices, polymer solar cells are lightweight, flexible, customizable on the molecular level and inexpensive to fabricate. But these advantages are balanced by their disadvantages: they offer about one third of the efficiency of other materials and experience substantial photochemical degradation.

“The high costs involved in inorganic photovoltaic materials have prevented these technologies from having a significant impact on global energy production,” Dr. Gupta said. “Organic photovoltaics like pervoskite solar cells (PSCs) and dye-sensitized solar cells (DSSCs) are being studied as potential alternatives, but they suffer from drawbacks including low power conversion efficiency and a short lifespan with real sensitivity to the environment.”

For their work, the research team focused on the cathode buffer layer (CBL), investigating architecture, materials and mechanisms of action to provide detailed insight into the opportunities for CBL improvement.

“The primary role of a CBL is to facilitate the collection of electrons at an electrode,” Dr. Patole said. “But it also performs several other tasks in making a solar cell function smoothly, including forming an electron selective and transport interlayer, blocking reverse charge carriers, and protecting the active layer from the hot metal atoms during thermal deposition of the cathode. For efficient organic solar cells, selecting an appropriate and high quality CBL is crucial.”

Per the researchers’ findings, an ideal CBL should be good at electron extraction and transport; have a suitable energy level that facilitates electron transport with high transparency and stability; and offer compactness for use in lightweight, flexible organic solar cells. One such material used is titanium oxide, a semiconducting metal oxide favored for its unique optical properties. Research has also found that adding cesium into the titanium oxide mix further improved device performance, while zinc oxide and zirconium oxide have also been studied.

“A diverse variety of organic materials, including conjugated polymers and small molecules, have also been explored as CBL in organic solar cells,” Dr. Gupta said.

“Small molecule-based layers offer advantages thanks to their well-defined molecular weight and the easy purification process. Quantum dots have also been explored because of their tunable optical and electrical properties, however, their commercial application is hindered by their sensitivity to the environment. Still, they remain interesting as an emerging class of nanomaterials with unique properties.”

The research team found that oxides and carbonates are popular as CBLs in organic solar cells, with zinc oxide one of the most widely used CBLs in high efficiency solar cells thanks to its chemical and thermal stability, favorable electronic and optical properties, and its low-cost fabrication. Metal and alkali fluorides, including calcium, barium, and lithium, are also popular as they improve performance in extracting electrons.

Additionally, organic solar cells can only harness sunlight from a narrow range of the electromagnetic spectrum, as ultraviolet and infrared photons can degrade the photoactive layer.

While CBLs can be used to resolve these issues and increase the lifetime of the devices, a CBL would need to perform dual functions, performing its duties at the cathode level and also in protecting the photoactive layer.

It is clear from the review paper that further improvements in performance are needed to allow polymer solar cells to compete with silicon cells, but efforts are being made to improve their viability in the photovoltaic market. The research offered by the team in their review paper will help researchers around the world develop these high efficiency cathode buffer layers for improved organic solar cell devices.��

Jade Sterling
Science Writer
31 March 2022

The post Engineered Cathode Buffer Layers for Highly Efficient Organic Solar Cells appeared first on Khalifa University.

For the third time in a decade, solar energy prices are tumbling in the Arabian Gulf. As demand for solar installations picks up dramatically, so falls the cost of solar energy, particularly in the Middle East.

Read Arabic story��.

When it comes to the cost of energy from new power plants, onshore wind and utility-scale solar are now the cheapest sources, costing less than gas, geothermal, coal or nuclear. Ten years ago, solar was the most expensive option for building a new power plant.

In a paper published in, KU researchers Dr. Harry Apostoleris, Post-Doctoral Fellow, Dr. Amal Al Ghaferi, Associate Professor, and Prof. Matteo Chiesa, Professor, show how local conditions and global macroeconomic factors have conspired to bring solar energy into a new realm of extreme affordability in the Middle East.

They argue that the Gulf market, especially the United Arab Emirates and Saudi Arabia, represents the leading edge of the global learning curve and offers a window into the likely near future of large-scale photovoltaics around the world.

As with most technologies, the more people invested in solar power, the cheaper it became. The Middle East has emerged as a global leader in photovoltaic deployment and pricing, with large utility-scale projects launched across the region.

In a previous study, the KU research team found that rapidly declining hardware prices, local business conditions, and access to generous financing packages were the major factors contributing to the low prices, with the market validating that assessment. Global average prices in comparable climates around the world have declined to nearly match the prices observed in the Gulf region, but now, countries in the GCC are seeing a new drop in prices. It is at this point that the researchers believe solar energy has solidified itself as the economically favorable energy source, continuing impressive price drops that began in 2016.

“If pricing at this level spreads around the world, simple business sense would suggest a rapid decarbonization of electricity generation, where coal and gas plants are retired as quickly as possible and replaced with photovoltaics, simply to save money,” explained Dr. Apostoleris. “The target of deep decarbonization by 2030 being held up by many climate scientists and advocates would suddenly enter the realm of feasibility with far less disruptive interventions than were previously believed necessary.”

Global learning curves are part of the cause of these price drops. The more that solar panels were produced, the more the technologies improved and economies of scale came into play. Fossil fuels in comparison can’t compete with this pace. Additionally, sunshine is free and in the Middle East, practically guaranteed every day. The costs of tapping into this solar power was bound to decline sharply as technology improved and the industry grew.

“The UAE leadership also deserves credit for recognizing the potential of solar energy and investing in it when many countries and entities were still sceptical,” said Dr. Apostoleris. “This is one of the main reasons why the UAE is ahead of the global curve in solar energy adoption.”

Often, the low prices are also secured as part of tenders for projects only implemented a couple years later, which further drives down prices for the projects to come after.

“Auction bids have been characterized by forward-looking cost projections—developers will tend to bid not based on the market price of hardware at the time of bidding, but on the prices they expect to pay a year or more in the future when the hardware is actually being ordered,” explained Dr. Apostoleris. “As strong downward pricing trends continue, this pattern of aggressive forward-bidding can be expected to hold.”

Additionally, the prominence of major international players in the Gulf’s solar development is helping to realize below-market costs. Large firms with an established presence in the region have�� relatively lower costs of doing business and are able to set their prices for large orders of hardware to a significant degree, and even factor in reputational elements—the ‘bragging rights’—of landing a large contract and gaining market share. Coupled with generous financing packages and a consistent solar resource, the low cost of solar energy in the Gulf begins to make sense.

“It is possible that developers accept lower margins in exchange for a benefit that larger projects provide for their overall business model,” explained Dr. Apostoleris. “The developer has its own learning curve, and building larger projects allows it to move faster down this learning curve and reduce its costs for future projects.”

For the KU researchers, the solar energy economics in the Gulf follow the same general patterns as global trends, but at a substantially advanced pace. They regard this as evidence that trends in the Gulf are best viewed not as an aberration but as an indicator of the how the global market is likely to evolve in the future.

“As the future increasingly appears to be one of previously unimaginably cheap energy, the future trajectory of this industry is exceptionally promising,” said Dr. Apostoleris. “This would herald a revolution in not only solar energy but in the energy sector generally, with a new age of ultra-cheap electricity transforming our lives, economies and environment. With such dramatic change on the horizon, it makes sense to consider the next steps to take full advantage of the coming energy transformation.”

In any energy revolution, there will be opportunities as well as challenges. Renewable energies are notoriously inconsistent throughout the day and the year, although less so in regions blessed with almost constant sunshine, such as the Middle East. The existing power grids don’t have the ability to distribute power from renewables over long distances, and storing power for use during the nights when power generation from solar is impossible is another major concern. These challenges of intermittency and geography are not insurmountable, but they do require investment to develop and build the necessary infrastructure.

“There are myriad ways to modify our energy systems to enhance the value of this low-cost solar electricity,” said Dr. Apostoleris. “This is before considering the potential of demand-side management strategies that aim to shift the energy demand curve to match the solar generation curve, minimizing the need for storage. However, this is a challenge that must be met not only from a technical perspective but also from that of society more broadly.”

It is clear that the Gulf solar market can offer a window into the likely future trajectory of photovoltaics globally. While the KU researchers point to a future of immense benefit, they also point out the challenges the market will face along the way. Thankfully, the region’s solar energy pioneers are rising to the challenge.

“Interestingly, in recent months, solar panel prices have actually risen for the first time in a decade,” added Dr. Apostoleris. “This seems to be caused by a bottleneck in the supply of polysilicon, the raw material for solar cells, as global demand increases. This might be an opportunity for the UAE to move into polysilicon production, leveraging cheap clean energy and the country’s central location to become a supplier, not just a consumer, of the solar industry.”

Researchers at Khalifa University are supporting the UAE in its advancement of regional knowledge and leadership in renewable energy, as the country announces ambitious and defined renewable energy targets. Innovative research taking place at Khalifa University is driving down costs and increasing the efficiency of solar cells, investigating the effects of climate change on renewable energy production, and even demonstrating the ability to provide solar energy 24/7.��

Jade Sterling
Science Writer
24 May 2021

The post What is Going on With Middle Eastern Solar Prices and What Does It Mean for the Rest of Us? appeared first on Khalifa University.