To probe the influence of molecular dipole on the open circuit voltage (VOC) of molecular heterojunction organic solar cells, we study axially fluorinated boron subphthalocyanine/fullerene (SubPc-F/C60) junctions. These exhibit an open-circuit voltage VOC=1.00V, a value closer to the HOMO–LUMO offset at the donor–acceptor interface=1.69eV than the VOC=1.06V measured for junctions between the archetypal chlorinated SubPc and C60, with corresponding HOMO–LUMO offset=1.84eV. Aside from the axial halogen substitution, the two compounds exhibit similar molecular structure and optical absorption. The energy levels and structure of the heteromolecular polaron pair are calculated, and the ideal organic diode model for SubPc-Cl is modified accordingly, successfully reproducing the experimental SubPc-F device characteristics. The reproducible difference in VOC is attributed to the different electric dipole strength between SubPc-F and SubPc-Cl and its influence on polaron pair dynamics at the heterojunction.

•We explore the Jsc/Voc tradeoff between conventional and inverted OPVs.•A Schottky junction forms between ITO and C60, increasing inverted OPV current.•The molybdenum trioxide – donor interface can be made to reflect excitons.•We demonstrate a 3.50% efficienct inverted organic photovoltaic.

In organic photovoltaic (OPV) cells, photocurrent generation relies on exciton diffusion to the donor/acceptor heterojunction. Excitons that fail to reach the heterojunction are lost to recombination via quenching at the electrodes or relaxation in the bulk. Bulk recombination has been mitigated largely through the use of bulk heterojunctions, while quenching at the metal cathode has been previously circumvented through the introduction of exciton blocking layers that “reflect” excitons. Here, we investigate an alternative concept of a transparent exciton dissociation layer (EDL), a single layer that prevents exciton quenching at the electrode while also providing an additional interface for exciton dissociation. The additional heterojunction reduces the distance excitons must travel to dissociate, recovering the electricity-generating potential of excitons otherwise lost to heat. We model and experimentally demonstrate this concept in an archetypal subphthalocyanine/fullerene planar heterojunction OPV, generating an extra 66% of photocurrent in the donor layer (resulting in a 27% increase in short-circuit current density from 3.94 to 4.90 mA/cm2). Because the EDL relaxes the trade-off between exciton diffusion and optical absorption efficiencies in the active layers, it has broad implications for the design of OPV architectures and offers additional benefits over the previously demonstrated exciton blocking layer for photocurrent generation.

We propose the use of high strength, metal-coated Kevlar yarns to weave flexible, conformal, and load-bearing antennas for an emerging class of applications emphasizing multiple functionality. In particular, here we present a unified, quantitative analysis of multiple properties of conductors as load-bearing materials in stress-, weight-, and shape-critical applications (e.g., in aerial vehicles), suggesting advantageous electrical conductor configurations to be metal-coated, multi-filament, high strength fibers. We then describe the fabrication of highly conductive metal coated Kevlar yarns, their mechanical and electrical properties, and the weaving of a flexible, stretchable, volumetric spiral antenna. The high frequency response of the antenna is found to match that of a traditionally made antenna comprised of electroplated copper on a rigid ceramic (Rogers TMM4) substrate. At low frequencies, the relatively lower conductivity of the metal-coated kevlar yarn leads to higher resistive losses compared to the traditional electroplated copper. We discuss strategies for mitigating such losses, and other means of improvement. More broadly, the results described here suggest a novel direction for multi-functional antenna design and applications, enabled by the superior mechanical characteristics of the composite conducting fibers, and the flexible, conformable, woven antenna architectures they help achieve.

The increasing sophistication of optoelectronic devices requires molecular-level dimensional control in the fabrication of multilayered structures with specifically engineered interfaces. However, the effectiveness of growth and doping strategies devised to achieve the desired device structures often remains unverified due to the lack of adequate characterization techniques. This is particularly true for devices based on conjugated organic compounds, which find increasing use in energy applications (e.g. organic light emitting diodes and organic photovoltaic cells, etc.). The buried interfaces are simply inaccessible or suffer damage when using conventional characterization techniques. In a current project, we address this challenge by advancing the development of low-energy (LE) SIMS for the analysis of organic-based optoelectronic materials systems.In the present study, multilayered organic thin films have been analyzed, varying experimental conditions such as the impact energies for Cs+ bombardment in the MCsx+ and M- mode on a Cameca Sc-Ultra instrument to investigate the ionization mechanisms as well as the atomic mixing at the interfaces between layers, and the degradation of the organic information. Low-energy dynamic SIMS proved to be a reliable tool for the characterization of organic multilayered optoelectronic devices: MCsx+ secondary ions provide information about the distribution of elements within the samples, while negative fragments that are characteristic for the different molecules give information about the structure. Copyright (C) 2010 John Wiley & Sons, Ltd.

Up to now, the analysis of organic or biological samples was mainly investigated using static SIMS, while dynamic SIMS was generally limited to the analysis of inorganic samples. The increasing sophistication of organic optoelectronic devices (e.g. organic light emitting diodes and organic photovoltaic cells, etc.) requires molecular‐level dimensional control in the fabrication of multilayered structures with specifically engineered interfaces. However, analytical tools for monitoring such fabrication precision are scarce. In a current project, we address this challenge by advancing the development of low‐energy Secondary Ion Mass Spectrometry (LE‐SIMS) for the analysis of organic‐based optoelectronic materials systems.