To address the growing energy needs concerning renewable, clean, and sustainable solar energy, organic solar cells (OSCs) have garnered considerable scientific attention. This is due to their distinct advantages in the development of flexible and portable devices, including affordability, lightweight design, and the feasibility of large-scale, printable fabrication.

Research in this regard has now led to the development of reliable organic solar cells that use wood materials. A collaborative effort by a team of scientists from Linköping University and the Royal Institute of Technology (KTH), Sweden, have demonstrated the potential of utilising untreated kraft lignin derived from wood pulp to enhance solar cells' environmental sustainability and reliability. 

The details regarding the team's study were published in the journal Advanced Materials. 

Sustainable solution

Researchers utilised one of the most prevalent organic materials found in nature, lignin, which proves to be a viable means of developing organic solar cells that are both stable and environmentally friendly.

At present, sunlight stands out as a primary source of sustainable energy. While traditional silicon-based solar cells are effective, their manufacturing involves a complex and energy-intensive process that poses the risk of potentially hazardous chemical spills, according to researchers. 

Organic solar cells are a rising research field due to their cost-effectiveness, lightweight, flexibility, and versatile applications, including indoor usage or integration into clothing for powering personal electronic devices. However, the sustainability quotient of such methods was questionable as organic solar cells are made of plastic or polymers derived from oil, which makes them organic but not environmentally friendly.  

"We want to build efficient, reliable, cheap, and environmentally friendly solar cells. This study enables us to show that this is possible and a first step towards replacing today's oil-based materials with wood-based alternatives," said Mats Fahlman, professor at the Laboratory of Organic Electronics (LOE) at Linköping University, in a statement. 

Kraft lignin

As a solution, scientists developed an organic solar cell in which a section of the electron transport layer, linking to the cathode, is crafted from kraft lignin directly extracted from wood pulp. While lignin currently constitutes a minor portion of the solar cell, the ultimate objective is to develop a solar cell predominantly composed of wood-derived materials, according to the team. 

Prior research has employed chemically modified wood-based materials to enhance the reliability and stability of organic and perovskite solar cells. In a recent study, Linköping researchers utilised unaltered kraft lignin directly extracted from wood during paper manufacturing. Collaborating with KTH, they examined the optimal molecular composition of lignin for this purpose.

"We have created a material, or composite, from kraft lignin which is to constitute the cathode interface layer. It turned out that this made the solar cell more stable. The advantage of kraft lignin is that it can create many hydrogen bonds, which helps to stabilise the solar cell," said Qilun Zhang, principal research engineer at LOE, in a statement.  

Organic solar cells are currently employed indoors and can replace batteries in low-energy devices and sensors. This marks the initial foray of organic solar cells into the market, with potential scalability for broader applications like large-scale energy supply.

Researchers say that constructing these cells from wood materials enhances their environmental friendliness. While organic solar cells may not achieve peak efficiency, their non-toxic, sustainable, and cost-effective nature, coupled with an efficiency range of 15% to 20%, proves ample for various applications.