“Being able to understand why something works is important for ensuring that effects are optimized to their full potential”
Polymer solar cells (PSCs) are a particularly good option for sustainability in the future because they are inexpensive to manufacture and may be both flexible and semitransparent. Ternary polymer solar cells have promising power conversion efficiency, although the reasons for this aren’t always evident. Now, these Ternary PSCs are being studied more closely by researchers from the University of Tsukuba and Hiroshima University.
While the PSC was running, the researchers conducted electron spin resonance (ESR) spectroscopy. They were able to observe the behaviour of electrons and holes when the cell was exposed to sunlight and obtain responses on a molecular level as a result of this.
PSCs typically have a p-type semiconductor combined with an n-type semiconductor. When sunlight shines on the cell, this blend provides the appropriate combination of charge carriers—holes and electrons—for a current to flow. These are called “Binary PSCs”. However, it has recently been discovered that adding an additional ingredient to the mix can improve the solar cell’s power conversion efficiency (PCE) and stability. They would be called “Ternary PSCs”. The problem is that no one has looked into it extensively until now.
“It has been reported that the accumulation of charge over time contributes to the performance of cells deteriorating,” explain study author Professor Itaru Osaka and study corresponding author Professor Kazuhiro Marumoto. “We therefore used ESR to look at a system made up of the polymer PTzBT and large molecule PC61BM. It has been found that adding an acceptor molecule, known as ITIC, to this system improves the PCE and the stability of the cell, so we looked closely at cells with and without ITIC to determine why.”
The short-circuit current reduced as a result of the accumulation of electrons in the PC61BM and holes in the PTzBT, according to the ESR spectroscopy experiment. The addition of ITIC to the active layer was found to minimise accumulation by improving the orientation of the chainlike PTzBT polymer molecules.
“By getting a molecular level picture of the effects of ITIC on a very promising PSC system, we believe we have taken a step closer to the commercial reality of polymer solar cells as part of a greener future”, says Professor Marumoto.
Read the entire study here.