Organic solar cells are devices that convert sunlight into electricity using carbon-based materials rather than silicon, as in conventional panels. They are flexible, cheaper to manufacture and suitable for large-scale production. However, the weak point is contacts based on self-assembled monolayers on the surface of indium tin oxide. Such contacts are easily degraded by light and heat, which hinders commercial use.
A group led by Ge Ziyi of the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences has developed a molecular lock strategy. They deposited a thin layer of an indium-chlorine compound in vacuum between the electrode and the hole-transporting layer. This layer triggers ligand exchange, a chemical reaction that produces a robust network of indium-oxygen-phosphorus bonds. It anchors the monolayer tightly and uniformly.
The work was published on October 21 in the journal Joule. Small cells made with this interlayer showed a power conversion efficiency of 20.4 percent. This coefficient is the share of sunlight that the device converts into electricity.
We scaled the method up to large modules with an area of 15.6 square centimeters and achieved a record active-area efficiency of 18.8 percent, the press release quotes Liu Quan, one of the authors, as saying.
The devices also demonstrated promising stability. After 2,000 hours of operation at maximum power and continuous illumination at 25 degrees Celsius, they retained more than 85 percent of their initial efficiency. Maximum power point tracking is a method in which operating conditions are continuously adjusted to draw the greatest possible power.
The authors believe the approach provides a universal platform for creating efficient, stable and scalable organic photovoltaic modules. In their view, it helps overcome the long-standing trade-off between efficiency, stability and scalability. At the same time, these are laboratory samples, not finished commercial products.