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CeNS Colloquium

Place: Adolf-von-Baeyer-Hörsaal, Butenandtstr. 5-13
Date: 28.1.11, Time: 15:30 h

Polymer Solar Cells: Status and Challenges

Prof. René Janssen
Molecular Materials and Nanosystems, Eindhoven University of Technology

 

Polymer solar cells offer an opportunity for low-cost, large area renewable energy production. Their power conversion efficiency depends on the quantum and energy efficiency by which photons from the sun are converted into current. To be efficient, absorption of light, charge generation, transport and collection all have to occur with high quantum efficiency and with minimal losses in energy. Presently, the best polymer solar cells reach power conversion efficiencies over 8% in solar light.

After a general introduction outlining the basic principles, design strategies for new conjugated polymers for efficient solar cells will be discussed. New materials will be presented that have extended optical absorption and feature high, balanced mobilities for charges. The new materials can be processed into efficient solar cells, depending on molecular weight and processing conditions.

Tandem solar cells form a promising strategy to further increase the power conversion efficiency of organic photovoltaics beyond the limits of single junctions. By combining the characteristics of representative single junction cells the optimal device layout can be accurately designed. Solution processed polymer tandem cells with an efficiency of higher than that of the corresponding single junctions have been obtained.

An important aspect of polymer solar cells is the nanoscale morphology of the active layer. High resolution three-dimensional electron tomography provides unprecedented insights into the actual heterojunctions present in hybrid polymer: metal oxide solar cells. The nanoscale morphology can be related to the device performance via exciton diffusion and exciton quenching, and the presence of suitable continuous percolation pathways for photogenerated charge carriers to reach the respective electrodes in both phases. The data provide a unique new insight in the operation of bulk heterojunction devices.