Impact of donor, acceptor, and blocking layer thickness on power conversion efficiency for small-molecular organic solar cells

We investigated the dependency of the power conversion efficiency on the thickness of donor (copper phthalocyanine; CuPc), acceptor (fullerene; C-60), and hole/exciton blocking (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline: BCP) layers in the OPV devices fabricated with double small-molecular layers. The power conversion efficiency peaked at a specific layer thickness, similar to 12.7 nm for the donor layer, similar to 17.5 nm for the acceptor layer, and similar to 8.0 nm for the hole/exciton blocking layer. This trend of power conversion efficiency was determined by short-circuit-current rather than open-circuit-voltage after light absorption. In addition, the donor layer thickness was more sensitive than the thickness of the acceptor or hole/exciton blocking layers in improving power conversion efficiency; i.e., similar to 330% for the donor layer, similar to 118% for the acceptor layer, and similar to 112% for the hole/exciton blocking layers. (C) 2009 Elsevier B.V. All rights reserved.