Researchers use wood materials to create reliable organic solar cells

One of nature’s most common organic materials, lignin, can be used to create stable and environmentally friendly organic solar cells. Researchers from Linköping University and the Royal Institute of Technology (KTH) have shown that raw kraft lignin can be used to make even more environmentally friendly and reliable solar cells. The study has been published In the diary Advanced materials.

Sunlight currently appears to be one of the main sustainable energy sources. Traditional solar cells made of silicon are efficient, but they have a complicated and energy-intensive manufacturing process that can lead to dangerous chemical spills. Therefore, organic solar cells have become a hot research area thanks to their low production cost, light weight and flexibility and therefore have many applications such as indoor use or attached to clothing to power personal electronic devices.

But one problem is that organic solar cells are made of plastic or petroleum-derived polymers. So even though they are organic, they are not as environmentally friendly as they could be.

Researchers from Linköping University and KTH have developed an organic solar cell in which part of the electron transport layer connected to the cathode of the solar cell is made of what is known as kraft lignin, obtained directly from wood pulp. . Although currently only a small part of the solar cell is made of lignin, the long-term goal is to build a solar cell made almost entirely of wood materials.

“We want to build efficient, reliable, economical and environmentally friendly solar cells. This study allows us to demonstrate that this is possible and is a first step towards replacing current petroleum-derived materials with wood-based alternatives,” he says. Mats Fahlman, professor at the Laboratory of Organic Electronics (LOE) at Linköping University.

In previous studies, chemically modified wood-based materials have been used to increase reliability or stability in both organic solar cells and solar cells made of perovskite crystalline material. In their recently published study, the Linköping researchers used a “raw” version of lignin, called kraft lignin, extracted directly from wood in the papermaking process. Together with KTH, they analyzed which molecular composition of lignin is most suitable for this purpose.

“We created a material, or composite, from kraft lignin that will make up the cathodic interface layer. It turned out that this made the solar cell more stable. The advantage of kraft lignin is that it has the ability to create many bonds of hydrogen, which helps stabilize the solar cell,” says Qilun Zhang, principal research engineer at LOE.

Organic solar cells are already used, mainly for indoor applications. They can also replace batteries in sensors and similar low-power devices. According to Fahlman, this is the first step towards the organic solar cell market. This technology can then be scaled up for broader applications, such as pure power delivery. And building them with wood materials would make the entire solar cell more environmentally friendly.

“Organic solar cells will never be the most efficient. But their advantage is that they are non-toxic, sustainable and cheap. If they are 15% to 20% efficient, that is more than enough for most applications” says Fahlman.