Reducing recombination losses in planar organic photovoltaic cells using multiple step charge separation

We enhance the efficiency of heterojunction organic solar cells by introducing a thin interfacial layer between the acceptor and donor layers. The interfacial layer energy levels are chosen to provide a gradient for charges crossing the interface, approximating a conventional p-n junction with three organic semiconductors. Devices with interfacial layers exhibit increased open circuit voltage (V(OC)) and increased short circuit current (J(SC)). The increase in V(OC) is due to a reduction in dark current and charge recombination. The increase in J(SC) is correlated with an increase in the conversion efficiency of excitons originating in the donor or acceptor layers. The interfacial layer destabilizes charge transfer states at the donor-acceptor interface, yielding reduced exciton recombination. The introduction of thin interfacial layers may prove to be an important probe of the physics of exciton separation in organic photovoltaic cells. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3585863]