L. Jay Guo

Plasmonic nanoresonators for high-resolution colour filtering and spectral imaging

Colour and spectral imaging systems typically use filters and glass prisms to disperse light of different wavelengths. With the miniaturization of integrated devices, current research on imaging sensors focuses on novel designs aiming at high efficiency, low power consumption and slim dimension, which poses great challenges to the traditional colourant-based filtering and prism-based spectral splitting techniques. In this context, surface plasmon-based nanostructures are attractive due to their small dimensions and the ability to efficiently manipulate light. In this article we use selective conversion between free-space waves and spatially confined modes in plasmonic nanoresonators formed by subwavelength metal-insulator-metal stack arrays to show that the transmission spectra through such arrays can be well controlled by using simple design rules, and high-efficiency colour filters capable of transmitting arbitrary colours can be achieved. These artificial nanostructures provide an approach for high spatial resolution colour filtering and spectral imaging with extremely compact device architectures.

Efficiency Enhancement of Organic Solar Cells Using Transparent Plasmonic Ag Nanowire Electrodes

Surface plasmon enhanced photo-current and power conversion efficiency of organic solar cells using periodic Ag nanowires as transparent electrodes are reported, as compared to the device with conventional ITO electrodes. External quantum efficiencies are enhanced about 2.5 fold around the peak solar spectrum wavelength of 560 nm, resulting in 35% overall increase in power conversion efficiency than the ITO control device under normal unpolarized light.

Flexible conjugated polymer photovoltaic cells with controlled heterojunctions fabricated using nanoimprint lithography

The authors describe conjugated polymer-based photovoltaic devices in which the shape and area of the interface between the electron donor and acceptor layers were controllably varied using nanoimprint lithography. The short circuit current is shown to increase with the interfacial area of the heterojunction, without affecting the open circuit voltage. The fill factor and power conversion efficiency are also shown to increase with donor-acceptor interfacial area.

Angle-Insensitive Structural Colours based on Metallic Nanocavities and Coloured Pixels beyond the Diffraction Limit

To move beyond colorant-based pigmentation display technologies, a variety of photonic and plasmonic crystal based structures have been designed and applied as colour filters. Nanostructure based colour filtering offers increased efficiencies, low power consumption, slim dimensions, and enhanced resolution. However, incident angle tolerance still needs to be improved. In this work, we propose a new scheme through localized resonance in metallic nanoslits by light funneling. Angle insensitive colour filters up to ±80 degrees have been achieved, capable of wide colour tunability across the entire visible band with pixel size beyond the diffraction limit (~λ/2). This work opens the door to angle insensitive manipulation of light with structural filtering.

Enhancement of Photovoltaic Response in Multilayer MoS2 Induced by Plasma Doping

Layered transition-metal dichalcogenides hold promise for making ultrathin-film photovoltaic devices with a combination of excellent photovoltaic performance, superior flexibility, long lifetime, and low manufacturing cost. Engineering the proper band structures of such layered materials is essential to realize such potential. Here, we present a plasma-assisted doping approach for significantly improving the photovoltaic response in multilayer MoS2. In this work, we fabricated and characterized photovoltaic devices with a vertically stacked indium tin oxide electrode/multilayer MoS2/metal electrode structure. Utilizing a plasma-induced p-doping approach, we are able to form p-n junctions in MoS2 layers that facilitate the collection of photogenerated carriers, enhance the photovoltages, and decrease reverse dark currents. Using plasma-assisted doping processes, we have demonstrated MoS2-based photovoltaic devices exhibiting very high short-circuit photocurrent density values up to 20.9 mA/cm(2) and reasonably good power-conversion efficiencies up to 2.8% under AM1.5G illumination, as well as high external quantum efficiencies. We believe that this work provides important scientific insights for leveraging the optoelectronic properties of emerging atomically layered two-dimensional materials for photovoltaic and other optoelectronic applications.

A Facile Route to Polymer Solar Cells with Optimum Morphology Readily Applicable to a Roll‐to‐Roll Process without Sacrificing High Device Performances

A new fabrication method for polymer solar cells that can produce optimized vertical distribution of components is reported. The favorable donor–acceptor morphology showing a well-organized photo-induced charge transporting pathway with fine nanodomains and high crystallinity is achieved. This process is also readily scalable to a large-area and high-speed roll-to-roll process without sacrificing high device performances, even without a PEDOT:PSS layer.

Photonic color filters integrated with organic solar cells for energy harvesting

Color filters are indispensable in most color display applications. In most cases, they are chemical pigment-based filters, which produce a particular color by absorbing its complementary color, and the absorbed energy is totally wasted. If the absorbed and wasted energy can be utilized, e.g., to generate electricity, innovative energy-efficient electronic media could be envisioned. Here we show photonic nanostructures incorporated with photovoltaics capable of producing desirable colors in the visible band and utilize the absorbed light to simultaneously generate electrical powers. In contrast to the traditional colorant-based filters, these devices offer great advantages for electro-optic applications.

Structural Colors: From Plasmonic to Carbon Nanostructures

In addition to colorant-based pigmentation, structure is a major contributor to a materials color. In nature, structural color is often caused by the interaction of light with dielectric structures whose dimensions are on the order of visible-light wavelengths. Different optical interactions including multilayer interference, light scattering, the photonic crystal effect, and combinations thereof give rise to selective transmission or reflection of particular light wavelengths, which leads to the generation of structural color. Recent developments in nanofabrication of plasmonic and carbon nanostructures have opened another efficient way to control light properties at the subwavelength scale, including visible-light wavelength selection, which can produce structural color. In this Concept, the most relevant and representative achievements demonstrated over the last several years are presented and analyzed. These plasmonic and carbon nanostructures are believed to offer great potential for high-resolution color displays and spectral filtering applications.

Fabrication and characterization of high Q polymer micro-ring resonator and its application as a sensitive ultrasonic detector.

Smooth sidewall silicon micro-ring molds have been fabricated using resist reflow and thermal oxidation method. High Q factor polymer micro-ring resonators have been fabricated using these molds. Quality factors as high as 105 have been measured at telecommunication wavelength range. By carefully examining the different loss mechanisms in polymer micro-ring, we find that the surface scattering loss can be as low as 0.23 dB/cm, much smaller than the absorption loss of the polystyrene polymer used in our devices. When used as an ultrasound detector such a high Q polymer micro-ring device can achieve an acoustic sensitivity around 36.3 mV/kPa with 240 μW operating power. A noise equivalent pressure (NEP) is around 88 Pa over a bandwidth range of 1–75 MHz. We have improved the NEP by a factor of 3 compared to our previous best result.

Bilayer metal wire-grid polarizer fabricated by roll-to-roll nanoimprint lithography on flexible plastic substrate

The bilayer metal wire-grid polarizer has several advantages over single-layer wire-grid polarizer and conventional polarizer since it provides higher polarization efficiency and can be easily fabricated. In this work, the authors demonstrate the fabrication of bilayer metal wire-grid polarizer on flexible plastic substrate by a continuous roll-to-roll nanoimprint lithography (R2RNIL) process and evaluate its performance. To fabricate wire-grid polarizer, subwavelength grating structure in epoxysilicone material is first created on a flexible PET substrate by UV R2RNIL followed by aluminum deposition. In initial measurement, extinction ratio exceeding 1000 has been achieved.