Researchers from the RIKEN Center for Emergent Matter Science found that change in structure and orientation of organic polymers greatly improves the efficiency of solar cells.
Within a polymer solar cell, the incoming energy of light is absorbed by the polymer causing electrons to become more excited and turning them into high-energy electrons. These electrons move through the polymer to the electrodes and produce an electrical current. The speed with which the electrons move determines how much of the energy is converted and how much of it is lost.
In their attempt to improve the efficiency of the conversion process, Itaru Osaka and his team decided to focus on a specific type of polymer, known as copolymer. It contains a very low soluble structure called PNNT-DT with repeating naphthodithiophene–naphthobisthiadiazole layers.
By attaching an additional alkyl side chains to the polymer, the team expected to improve its solubility. What came as a surprise to them was to find that this modification also improved the power conversion efficiency of solar cells that contain the polymer.
The improvement in efficiency of almost 3%, the team explained by the different arrangement of the polymer within the solar cells. As opposed to the perpendicular alignment of the typical polymers, the new alkylated polymers were arranged in a way that the polymer chains are flat and in stacks on the surface of the thin film.
The next step for the team is to find other polymers that will increase the efficiency of the polymer solar cells to a point that it is compatible with this of typical inorganic solar cells. Their aim now is to explore the reasons to why this change in orientation occurs, so that they can implement the technology to other polymers, with greater abilities to absorb light.
