We explore the dependence of the dark current of C(60)-based organic photovoltaic (OPV) cells on molecular composition and the degree of intermolecular interaction of several molecular donor materials. The saturation dark current density, J(S), is an important factor in determining the open circuit voltage, V(oc). The V(oc) values of OPVs show a strong inverse correlation with J(S). Donor materials that show evidence for aggregation in their thin-film absorption spectra and polycrystallinity in thin film X-ray diffraction result in a high dark current, and thus a low V(oc). In contrast, donor materials with structures that hinder intermolecular pi-interaction give amorphous thin films and reduced values of J(S), relative to donors with strong intermolecular pi-interactions, leading to a high V(oc). This work provides guidance for the design of materials and device architectures that maximize OPV cell power conversion efficiency.

Highly porous (V(mesopore) = 25-50%) and ordered mesoporous titania thin films (MTTF) were prepared on ITO (indium tin oxide)-covered glass by a fast two-step method. The effects of substrate surface modification and thermal treatment on pore order, accessibility and crystallinity of the MTTF were systematically studied for MTTF deposited onto bare and titania-modified ITO. MTTF exposed briefly to 550 °C resulted in highly ordered films with grid-like structures, enlarged pore size, and increased accessible pore volume when prepared onto the modified ITO substrate. Mesostructure collapse and no significant change in pore volume were observed for MTTF deposited on bare ITO substrates. Highly crystalline anatase was obtained for MTTF prepared on the modified-ITO treated at high temperatures, establishing the relationship between grid-like structures and titania crystallization. Photocatalytic activity was maximized for samples with increased crystallization and high accessible pore volume. In this manner, a simple way of designing materials with optimized characteristics for optoelectronic applications was achieved through the modification of the ITO surface and a controlled thermal treatment.

2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) is used as a donor material in vapor deposited organic heterojunction photovoltaic cells. Devices with the structure indium tin oxide/SQ (x)∕C60 (400Å)/bathocuproine (100Å)∕Al (1000Å), where x=65, 110, 150, and 200Å were compared. Devices with x=65Å exhibited a power conversion efficiency of 3.1% under 1sun, AM1.5G simulated solar irradiation, giving an open circuit voltage of 0.76±0.01V, a short circuit current of 7.01±0.05mA∕cm2, and a fill factor of 0.56±0.05. Thicker SQ films lead to lower short circuit currents and fill factors, giving conversion efficiencies in the range of 2.6% to 3.2%. The demonstration of sublimable SQ as a donor material opens up a family of compounds for use in small molecule based heterojunction photovoltaics.

Small‐molecule solar cells are demonstrated using Pt and Pd tetraphenylbenzoporphyrin as donor materials. High efficiencies are achieved, and the effects of triplet excited state diffusion are studied. The solubility of these molecules allows for the fabrication of solution processed solar cells with relatively high performance.