Pushing organic solar cell efficiency past 18%

A joint research team from National Taiwan University, National Yang Ming Chiao Tung University, and National Tsing Hua University has discovered a precise molecular engineering strategy. By adjusting the side chains of organic materials, the team has achieved a power conversion efficiency of 18.13%.

Solar power is essential for a sustainable future. Scientists are working hard to improve organic photovoltaics (OPVs) because they are lightweight and flexible. These carbon-based solar cells can be printed on thin films. However, making them efficient enough for real-world use remains a challenge. A collaborative study published in Advanced Functional Materials has now provided a clear road map to higher efficiency.

Collaboration and molecular design approach

The breakthrough comes from a partnership between three universities in Taiwan. The team includes researchers from National Taiwan University (NTU), National Yang Ming Chiao Tung University (NYCU), and National Tsing Hua University (NTHU). Each university brought a unique piece of the puzzle to solve a complex problem regarding molecular fit.

The researchers focused on a specific type of material called a non-fullerene acceptor. These materials accept electrons to create an electric current. The team created a series of “C-shaped” molecules named the CB series. Their goal was to see how the length of the flexible side chains attached to these molecules changed their performance.

Think of these molecules as puzzle pieces that need to lock together perfectly. They also need to mix well with a donor polymer called PM6. The side chains act like the arms of the molecule. They determine how close the molecules can sit next to each other.

Testing different molecular structures

The chemistry experts at NYCU synthesized four versions of these molecules with different arm lengths. They named them CB8, CB12, CB16, and CB20. This allowed the alliance to determine the optimal length.

If the arms are too short, the molecules clump together too tightly. This traps the electricity. If the arms are too long, the molecules are pushed too far apart. This breaks the pathway for the current.

The team found that the CB16 molecule was the perfect balance. It reduced clumping while keeping the molecules connected enough to transport power efficiently.

Advanced analysis and validation

Validating this “Goldilocks” molecular design required advanced physics and structural analysis from the partner universities.

The team at NTU provided critical insight into how fast the electricity moves. They used a technique called ultrafast transient absorption spectroscopy. This acts like a high-speed camera that can track electrons in mere picoseconds. Their data prove that the CB16 device allowed electrical charges to transfer faster than the other versions. This speed is a major reason for the high efficiency.

Simultaneously, the researchers from NTHU used powerful X-ray scattering at the National Synchrotron Radiation Research Center of Taiwan. This allowed them to look deep inside the material structure. They confirmed that the CB16 molecule formed a smooth and interconnected network with the donor polymer.

Results and future implications

The result of this three-way collaboration is a solar cell with an impressive efficiency of 18.13%. This is one of the highest values reported for this type of device. The device also showed great durability and kept its performance even after being heated for a long time.

This study proves that combining synthesis, physical analysis, and structural science is the key to better energy technology.

“This comprehensive study demonstrates that precise control over molecular architecture is the key to unlocking the next generation of high-efficiency solar energy,” says co-corresponding author Dr. Pi-Tai Chou, professor of chemistry at National Taiwan University.