Carsten Borek

Molecular and Morphological Influences on the Open Circuit Voltages of Organic Photovoltaic Devices

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.

Photophysics of Pt-porphyrin electrophosphorescent devices emitting in the near infrared

The triplet annihilation dynamics of near infrared organic light-emitting devices are studied with peak electrophosphorescence at a wavelength of 772nm using a platinum-porphyrin derivative Pt(II)-tetraphenyltetrabenzoporphyrin as dopant. Both the photoluminescent decay transients of the thin films and the quantum efficiency versus current density characteristics of devices using tris(8-hydroxyquinoline) aluminum or 4,4′-bis(N-carbazolyl)biphenyl (CBP) as hosts are fitted by a model based on triplet-triplet annihilation. When the phosphor is codoped with Ir(III) bis(2-phenyl quinolyl-N,C2′) acetylacetonate in CBP, the quantum efficiency is enhanced, and the observed decrease of efficiency at high current densities is explained by field-induced charge pair dissociation. The external quantum efficiency has a maximum of (8.5±0.3)%, decreasing to (5.0±0.3)% at 1mA∕cm2.

Near-Infrared Phosphorescent Polymeric Nanomicelles: Efficient Optical Probes for Tumor Imaging and Detection

We report a formulation of near-infrared (near-IR) phosphorescent polymeric nanomicelles and their use for in vivo high-contrast optical imaging, targeting, and detection of tumors in small animals. Near-IR phosphorescent molecules of Pt(II)-tetraphenyltetranaphthoporphyrin (Pt(TPNP)) were found to maintain their near-IR phosphorescence properties when encapsulated into phospholipid nanomicelles. The prepared phosphorescent micelles are of approximately 100 nm size and are highly stable in aqueous suspensions. A large spectral separation between the Pt(TPNP) absorption, with a peak at approximately 700 nm, and its phosphorescence emission, with a peak at approximately 900 nm, allows a dramatic decrease in the level of background autofluorescence and scattered excitation light in the near-IR spectral range, where the signal from the phosphorescent probe is observed. In vivo animal imaging with subcutaneously xenografted tumor-bearing mice has resulted in high contrast optical images, indicating highly specific accumulation of the phosphorescent micelles into tumors. Using optical imaging with near-IR phosphorescent nanomicelles, detection of smaller, visually undetectable tumors has also been demonstrated.

P‐204: Distinguished Poster Paper: A Near Infrared OLED for Day/Night Display

Recently there has been a growing interest in OLEDs that emit in the near infrared region (700–1250nm) for covert night vision applications. Here we report our results on a highly efficiency phosphorescent metalloporphyrin OLED device with a λmax= 765 nm. We will demonstrate a bi-color day/ covert night active matrix display fabricated on flexible metal using this material for the IR pixel.

Organic Materials for Solar Photovoltaics

Metalloporphyrins and subphthalocyanines make excellent donor/acceptor materials in OPVs, some with high open circuit voltages (Voc). The properties of these devices and model for understanding the origin of Voc for OPVs will be presented.

Taking a Visible Step Forward into the Non-Visible (Infrared) Region

This presentation focuses on our most recent work in the area of red to near-IR emitting OLEDs. The discussion will include descriptions of emitter design, device structures, external efficiencies and lifetimes of these devices.