How Can We Improve Solar Energy Harvesting?

Solar energy is essential for a sustainable future, but traditional silicon-based solar panels have limitations, such as high cost and difficulty mounting on curved surfaces.

Although solar energy can be harnessed by solar panels mounted on residential and commercial properties alike (source: Electron Green) there are limitations and there are specific options and considerations.

Researchers are exploring alternative materials to overcome these drawbacks.

One promising option is “organic” semiconductors, which are carbon-based, abundant, affordable, and environmentally friendly.

What Are the Advantages of Organic Semiconductors?

Organic semiconductors can be applied to various surfaces using solution-based methods, similar to painting a wall.

“These materials can potentially reduce production costs for solar panels and can be customised to absorb light at specific wavelengths, making them ideal for transparent or coloured solar panels,” said Wai-Lun Chan, a physics and astronomy professor at the University of Kansas. These characteristics make organic solar panels suitable for next-generation green buildings.

Lauren Davies of VoIP company bOnline comments: “As the technology we use to harness energy moves forward and advances at a remarkable pace, all industries will be affected, mainly positively by these changes. For example, energy intensive businesses, such as those with data centres may turn to cheaper and more efficient methods of energy production and storage.”

What Makes Non-Fullerene Acceptors Special?

Organic semiconductors have been used in display panels for consumer electronics but not widely in commercial solar panels due to their low efficiency. However, the introduction of non-fullerene acceptors (NFAs) has changed this.

NFAs have pushed the efficiency of organic solar cells closer to 20%, compared to the 12% efficiency of traditional organic cells and 25% for single crystalline silicon cells.

Breakthrough in Understanding

Despite their performance, the scientific community was unclear why NFAs outperformed other organic semiconductors. A study led by Chan and his team, including graduate students Kushal Rijal and Neno Fuller, revealed a microscopic mechanism behind the efficiency of NFAs.

Using time-resolved two-photon photoemission spectroscopy (TR-TPPE), they tracked the energy of excited electrons with sub-picosecond resolution. They discovered that some excited electrons in NFAs gain energy from their environment rather than losing it, which is counterintuitive to typical behaviour.

Can Entropy Boost Solar Efficiency?

The team’s findings suggest that the quantum behaviour of electrons allows an excited electron to exist on several molecules simultaneously.

This, coupled with the Second Law of Thermodynamics, which states that all physical processes increase total entropy, results in an unusual energy gain process.

“In most cases, heat transfers from hot to cold objects to increase entropy. However, we found that in specific nanoscale structures, this process reverses, allowing neutral excitons to gain heat and separate into positive and negative charges, producing electrical current,” Rijal explained.

Future Implications

The entropy-driven charge separation mechanism discovered could enable organic solar cells with NFAs to achieve higher efficiency.

Understanding this mechanism could help researchers design new nanostructures to harness entropy for directing energy flow on the nanoscale. Additionally, this discovery might lead to more efficient photocatalysts for solar-fuel production, converting sunlight and carbon dioxide into organic fuels.

In short, the study demonstrates how harnessing entropy and quantum behaviour in organic semiconductors can significantly improve solar energy harvesting, paving the way for more efficient and sustainable energy solutions.