Highly Efficient Charge Collection in Bulk-Heterojunction Organic Solar Cells by Anomalous Hole Transfer and Improved Interfacial Contact.

The dilute donor-fullerene bulk heterojunction (BHJ) has been proven to be an efficient architecture of organic solar cells. However, the hole-extraction pathway and the origin of the high open-circuit voltage ( VOC) in this peculiar architecture remains elusive. Direct evidence is provided here that the photogenerated holes can be extracted via the acceptor phase even under the operating conditions. Meanwhile VOC is found to be closely correlated with the surface composition at the MoO3/BHJ interface. Extending these findings into device optimization, more than 37% enhancement is achieved in a prototype BHJ device. These results evoke renewed insight into the underlying physics in organic solar cells.