Yiying Zhao

Enhanced optical field intensity distribution in organic photovoltaic devices using external coatings

An external dielectric coating is shown to enhance energy conversion in an organic photovoltaic cell with metal anode and cathode by increasing the optical field intensity in the organic layers. Improved light incoupling in the device is modeled using transfer matrix simulations and is confirmed by in situ measurement of the photocurrent during growth of the coating. The optical field intensity in optimized cell geometries is predicted to exceed that in analogous devices using indium tin oxide, both cell types having equivalent anode sheet resistance, suggesting a broader range of compatible substrates (e.g., metal foils) and device processing techniques.

Scanning optical probe microscopy with submicrometer resolution using an organic photodetector

A high-resolution scanning optical microscopy technique is demonstrated, in which an organic photodetector on a silicon-based scanning probe cantilever scans a sample, simultaneously recording optical and topographic data with submicrometer resolution, while showing no measurable degradation during the scan. Potential applications of the probe include characterization of optoelectronic materials and devices, as well as simultaneous topographic and fluorescence microscopy of biological samples. Extension to these applications is aided by the fact that the probe is compatible with conventional atomic force microscopy systems and does not suffer some of the practical difficulties of existing near-field scanning optical microscopy systems.

Organic light-emitting device on a scanning probe cantilever

Organic light-emitting devices (OLEDs) were fabricated on scanning probe cantilevers using a combination of thermally evaporated molecular organic compounds and metallic electrodes. Ion beam milling was used to define the emissive region in the shape of a ring having a diameter of less than 5μm and a narrow width. Stable light emission was observed from the device at forward bias, with a current-voltage response similar to that of archetypal OLEDs. Based on this device, a novel electrically pumped scanning optical microscopy tool is suggested.

OLEDs on fibers and AFM cantilevers

This talk will discuss recent work on novel device architectures that include ITO-free OLEDs deposited on fibers, on highly corrugated surfaces and sharp tips for for solid-state lighting and microscopy applications.

Scanning probe optical microscopy using an integrated submicron organic photodetector

A high-resolution scanning optical microscopy technique is developed by using focused ion beam milling and vacuum thermal evaporation to fabricate an organic photodetector with sub-micron size on a scanning probe cantilever. Optical and topographic data are recorded simultaneously and demonstrate sub-micron resolution. Potential applications of the probe include materials characterization, biology, and nanophotonics, and are aided by the fact that the probe is compatible with conventional atomic force microscopy (AFM) systems and does not suffer some of the practical difficulties of existing near-field scanning optical microscopy (NSOM) systems.

Cantilevers with integrated organic LEDs for scanning probe microscopy

Organic thin films which are based on Van der Waals-bonded molecular organic compounds can be deposited onto a variety of substrates including scanning probe cantilevers without the lattice-matching constraints of conventional covalently-bonded semiconductors. Here we demonstrate organic light-emitting devices (OLEDs) fabricated on scanning probe cantilevers using thermal evaporation of molecular organic compounds and metallic electrodes. Ion beam lithography was used to define the emissive region in the shape of a ring having a diameter of 5 micrometers. The width of the ring emission was less than a micron as measured in the far field. Stable light emission was observed from the device at forward bias, with a current-voltage response similar to that of archetypal OLEDs. Such a probe can enable a new form of electrically-pumped SNOM compatible with existing atomic force microscopy tools and techniques. The emission wavelength can be tuned across the entire visible spectrum, including white light emission, by altering the composition of the emissive layer with a wide range of luminescent dyes. Should the ring-shaped light emission be used for imaging, the sample image can be deconvolved using a ring filter to achieve high resolution. The OLED probe can also be used to transfer excitons through the cathode to a sample via plasmon-assisted energy transfer; such a probe would be valuable for studying exciton dynamics in organic or organic/inorganic hybrid photovoltaic devices. By demonstrating the first active organic device on a scanning probe cantilever, this work opens the door to a wide range of new scanning probe techniques based on this class of materials for areas such as biological imaging.