Researchers at the University of Kansas say that carbon-based materials could make solar panels work better and be easier to install.
Solar energy is vital for a sustainable future, but traditional silicon solar panels, commonly used due to their semiconductor properties, are costly and challenging to mount on curved surfaces. To overcome these issues, researchers at the University of Kansas have developed alternative materials for harvesting solar energy. Their focus on “organic” semiconductors, which are carbon-based and plentiful on Earth, offers a promising, cost-effective, and environmentally friendly solution.
In organic semiconductors, electrons typically bind to their positive counterparts known as “holes,” forming electrically neutral quasiparticles called “excitons” when light is absorbed. However, introducing a new class of organic semiconductors, non-fullerene acceptors (NFAs), has shifted this dynamic. Organic solar cells incorporating NFAs have approached efficiencies near the 20% mark, a significant improvement over traditional figures.
Despite their enhanced performance, the scientific community had been unclear about why NFAs substantially outperform other organic semiconductors. The team uncovered a microscopic mechanism that partly explains the superior performance of NFAs.
The breakthrough came through measurements using a technique called “time-resolved two-photon photoemission spectroscopy” (TR-TPPE). This method enabled the researchers to observe the energy of excited electrons with extremely high temporal resolution, less than a trillionth of a second, shedding light on the dynamic processes within NFAs that contribute to their high efficiency.
The team attributes this unique process to the quantum behaviour of electrons on a microscopic scale, which enables an excited electron to be present on multiple molecules simultaneously. This quantum phenomenon works alongside the Second Law of Thermodynamics, which dictates that every physical process increases the total entropy, or “disorder,” resulting in an unusual energy gain process.
From their experimental results, the team suggests that this entropy-driven charge separation mechanism significantly enhances the efficiency of organic solar cells made with NFAs. Moreover, the researchers believe that this mechanism could be applied to develop more efficient solar cells and to design better photocatalysts for solar-fuel production. This involves using sunlight to convert carbon dioxide into organic fuels, leveraging the photochemical process enhanced by the newly discovered mechanism.
Reference: Kushal Rijal et al, Endothermic Charge Separation Occurs Spontaneously in Non‐Fullerene Acceptor/Polymer Bulk Heterojunction, Advanced Materials (2024). DOI: 10.1002/adma.202400578
