Events

Factors influencing photocurrent generation in organic bulk heterojunction solar cells: interfacial energetics and blend microstructure

April 29, 2009 at 3pm/36-428

Jenny Nelson
Department of Physics Imperial College London

abstract:
The efficiency of photocurrent generation in conjugated polymer:small molecule blend solar is strongly influenced both by the energy level
alignment at the donor-acceptor interface and by the microstructure of the blend films. Photoinduced charge separation requires that the charge
separated state competes successfully with other excited states in the system and that the thermodynamic driving force for charge separation
exceeds some threshold, which may depend upon both the specific chemical structure and the local microstructure. The optimum blend microstructure, in turn, appears to combine a high degree of order in local molecular packing (benefitting charge transport and charge separation), a large interface (for charge separation) and significant phase segregation (to minimise charge recombination). In this work, we will show how a combination of spectroscopic techniques, electrical measurements and studies of phase behaviour can be used to build up a picture of the microstructure in a polymer: fullerene blend film, and so to rationalise the conditions for photocurrent generation. Finally, we demonstrate that the optimum blend composition for photocurrent generation can be related in a rational way to the phase behaviour of the binary system and in particular to the self-organising tendency of the component materials.

bio:
Jenny Nelson is a Professor of Physics at Imperial College London, where she has researched novel types of solar cell since 1989. Her current research focuses on photovoltaic energy conversion using molecular materials, characterization of the charge transport, charge separation and morphology properties of molecular semiconductors, and the modelling of charge transport in organic semiconductors. She has published over 100 papers on photovoltaic materials and devices and a book on the physics of solar cells.