Contact Information

Dr. Bruce Alphenaar
Department of Electrical & Computer Engineering
University of Louisville
Louisville, KY 40292
Phone: 502-852-1554
Email: brucea@louisville.edu

Photocurrent Spectroscopy of Exciton Formation and Dissociation in Organic Solar Cells

In organic solar cells, photovoltage is generated as excitons dissociate across the interface between a light absorbing material and a charge accepting contact. This requires that the dissociation process favors injection of a particular charge type (either positive or negative), and that dissociation occurs more readily than recombination across the interface. The interface properties are clearly very important in determining the solar cell efficiency. However, it is difficult to study the efficiency of charge formation and separation across a single interface, independent of the entire charge transfer process involved in generating the photovoltage.

Here we propose a new photocurrent spectroscopy technique entitled Displacement Photocurrent Spectroscopy (DPS) for measuring charge formation and separation across a single interface. Pulsed laser light is directed at the contact interface of an organic solar cell deposited on a insulating quartz substrate. Charge separation across the interface produces an ac displacement current, which can be measured with a lock-in amplifier, synched to the laser repetition rate. Varying the repetition rate of the laser and electric field across the interface will allow us to isolate the charge transfer mechanism, and identify the influence of different contact materials to the solar cell operation. By using a spin filtering material at the interface, we will also be able to probe exciton triplet states, and study their influence on the solar cell efficiency.