Mixed donor-acceptor molecular heterojunctions for photovoltaic applications. II. Device performance

We demonstrate efficient organic photovoltaic cells employing a photoactive region composed of a mixed donor-acceptor molecular layer, the properties of which were introduced in the preceding paper (Part I) [Rand et al., J. Appl. Phys. 98, 124902 (2005)]. The hybrid planar-mixed heterojunction (PM-HJ) device architecture consists of a film mixture of donor and acceptor molecules inserted between layers of pure donor and acceptor composition. Using the donor, copper phthalocyanine, and the acceptor, ${\mathrm{C}}_{60}$ , we demonstrate a hybrid PM-HJ cell with a maximum power conversion efficiency of $(5.0\pm 0.3)\%$ under $1–4\mathrm{suns}$ simulated AM1.5 solar illumination. The current-voltage characteristics of the PM-HJ cell are described using a model based on the field-dependent charge collection length.