Solar energy gets a boost this week as RIKEN researchers have now discovered that adding fluorine atoms to light harvesting polymers improves their efficiency. This is a breakthrough for companies manufacturing photovoltaic cells and products as performance in flexible solar cells can now be enhanced even more.

Typically, a polymer solar cell absorbs light through the use of a semiconducting polymer, which changes the electrons within the molecules from ground state to an excited state.  The chosen material then directs the electrons to an electrode where an electrical current is generated. These semiconducting polymers are great because they are lightweight and flexible as well as being semi-transparent. For this reason, they would be perfect for use in low-cost PV panels.  But currently, even the best polymer solar cells only convert around 10 percent of light, which is pretty weak.

However, Itaru Osaka and colleagues at the RIKEN Center for Emergent Matter Science have now demonstrated that fluorine atoms offer potential improvements in this area.  They formed two polymers: PNTz4TF2 and PNTz4TF4. From their research, they found that adding fluorine lowered the energy level in the polymer which resulted in higher output voltage and less energy loss throughout the system. In particular, in the PNTz4TF2 the polymer strands were more rigid which allowed a faster movement of electrical charge flowing through.

Each polymer was then mixed with an electron acceptor (PC71BM) to see how it would react. With the PNTz4TF2 the team managed to achieve an efficiency of around 10.5 percent, which is only slightly better than a fluorine-free polymer, but an increase nonetheless.  The researchers are also feeling confident this can be improved further with a little more time and research and we may even see efficiency reach to as high as 15 percent.

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