Co-evaporant induced crystallization of zinc phthalocyanine: C60 blends for solar cells

Donor-acceptor small molecule blends are a key component of efficient organic solar cells. Their efficient function in terms of exciton transport, exciton separation, and carrier transport is critically dependent on morphology, which is especially difficult to control when the layers are prepared by vacuum evaporation. We investigate co-evaporant induced crystallization for a blend of zinc phthalocyanine (ZnPc) and C60 in single layers and organic solar cells. Polydimethylsiloxane (PDMS) is chosen as an additive and simultaneously evaporated during the deposition of the blend layer on a heated substrate. Grazing incidence X-ray diffraction measurements prove a strong increase in crystallinity upon co-evaporation. Laser desorption/ionization time-of-flight mass spectrometry measurements identify remainders of PDMS in the co-evaporated layers, demonstrating that PDMS is incorporated into the film. Nevertheless, co-evaporated ZnPc:C60 solar cells show improved short circuit current densities, fill factors, and power conversion efficiencies.