Ultrafast spectroscopy of polaron pairs in polymer solar cells

We use a femtosecond two step photocurrent technique to study the role of bound polaron pairs during charge carrier generation in two different conjugated polymer/fullerene blend systems. In pure MeLPPP and in pure MDMO-PPV polaron pairs are formed and can be dissociated via reexciting with a second laser pulse tuned to the respective polaron absorption band. When blended with a fullerene, however, bound polaron pairs are only formed in MeLPPP/PCBM while they do not play a role in the PPV sample.