“By using a large variety of techniques we reveaed the nanoscale morphology for a specific material combination and show how it relates to performance.”

It is the first comprehensive study that relates the morphology of the active layer of polymer solar cells to their performance. Although the details are probably different for other material combinations, the main insight that morphology and performance are strongly correlated is the accepted conclusion regarding polymer solar cells.

The paper shows that, by combining morphological and optical studies with device testing, it is possible to obtain an insight into the interplay of morphology and performance. This was anticipated by the polymer solar cell community, but the results shown in the paper give conclusive evidence that it is actually true.

In polymer solar cells, one usually employs a blend of two polymer or organic materials with complementary electronic properties in order to be able to create and transport positive and negative charges. The performance of these composite layer solar cells strongly depends on the charge generation at the interface of these two materials and on the percolation paths for charge transport. By using a large variety of techniques, we revealed the nanoscale morphology for a specific material combination and described how it relates to performance.

That is a long story. It dates back to 1993, when I spent a year at the University of California Santa Barbara with the Nobel Laureate Alan Heeger. At UCSB, Alan Heeger and Niyazi Serdar Sariciftci, were the first to explore polymer solar cells based on blends of polymers and fullerenes. At UCSB, I became involved in photophysical studies of this combination material. Serdar Sariciftci, Kees Hummelen, (one of the co-authors of the paper; also at UCSB in the early days) and I, continued our research in this area at the end of ‘90s, with funding provided by the European Commission and the Dutch government.