Charge Generation in Donor Acceptor Blends

In order to uncover the photophysical processes and the loss mechanism in polymeric solar cells, two main approaches can be distinguished electrical measurements and time-resolved optical spectroscopy. Electrical measurements have the fundamental disadvantage that they lack time and spatial resolution to probe the processes that occur directly after exciton ionization. To investigate these dynamics, time-resolved spectroscopy is a much more promising approach, because ultrafast laser systems allow observing these proeesses directly with subpicosecond time resolution. 

The work on PCBMipolythiophene blends underlines that, in order to increase the efficiency of organic solar cells, the kinetics of the charge-transfer state are a key factor. To improve device efficiency the rate of charge-transfer state recombination should be reduced and the rate of separation of charges from the charge-transfer state should be increased. In order to modify these rates the mechanisms by which the processes occur must be understood in greater detail. 

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