Researchers use wood materials to create reliable organic solar cells

One of the most common organic materials in nature, 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 untreated kraft lignin can be used to make solar cells even more environmentally friendly and more reliable. The study was published in the journal Advanced materials.

Sunlight currently appears to be one of the main sources of sustainable energy. Traditional solar cells made from silicon are efficient, but their manufacturing process is complex and energy-intensive, which can lead to hazardous chemical spills. Organic solar cells have therefore become a hot area of ​​research 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 the problem is that organic solar cells are made of plastic or polymers derived from petroleum. So although 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 consists of so-called kraft lignin, coming directly from wood pulp. Although only a small part of the solar cell is currently 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, cheap and environmentally friendly solar cells. This study allows us to show that this is possible and constitutes a first step towards replacing current petroleum-based materials with oil-based alternatives. of wood,” says Mats Fahlman, professor at the Laboratory for Organic Electronics (LOE) at Linköping University.

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

“We created a material, or composite, from kraft lignin that is to make up the cathode 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 hydrogen bonds, which helps stabilize the solar cell,” explains Qilun Zhang, senior research engineer at LOE.

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

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