Enhanced performance of single and double junction plastic solar cells

PhD ceremony: Mr. D.J.D. Moet, 13.15 uur, Doopsgezinde kerk, Oude Boteringestraat 33, Groningen

Dissertation: Enhanced performance of single and double junction plastic solar cells

Promotor(s): prof. P.W.M. Blom

Faculty: Mathematics and Natural Sciences

In the most efficient plastic solar cells to date, sunlight is absorbed in an ultrathin layer of a semiconducting polymer mixed with an n-type organic material. Collected photons are directly converted into electricity via the complex processes of generation, dissociation, transport and extraction of electric charges. The power conversion efficiency of plastic solar cells strongly depends on the optical and electronic properties of the utilized polymer. In many cases, the performance is limited due to impediments in one or more of the processes mentioned above.

This work studies the device physical origin of such performance limitations for various polymer-based photovoltaic systems and discusses how these can be minimized. Based on experimental characterization and device modeling, it is shown how molecular weight, choice of processing solvent and chemical side-reactions during fabrication can affect the operation of single-layer plastic solar cells.

Moreover, we show that in specific cases optical and electronic losses can be reduced simultaneously by using a device structure with two photoactive layers. Careful design of the required middle electrode enables such double junction cells to show enhanced performance compared to optimized single layer devices. These results and the outcome of extensive optoelectronic modeling path the way towards efficient solution-processed tandem polymer solar cells that contain two complementary absorbing photoactive layers.