Nanoparticle-based plasmonic organic photovoltaic devices

Surface plasmons excited by light in metal structures provide a means for manipulating optical energy at the nanoscale Plasmons are associated with the collective oscillations of conduction electrons in metals and play a role intermediate between photonics and electronics As such, plasmonic devices have been created that mimic photonic waveguides as well as electrical circuits operating at optical frequencies We review the plasmon technologies and circuits proposed, modeled, and demonstrated over the past decade that have potential applications in optical computing and optical information processing

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Plasmonic circuits for manipulating optical information

We present the numerical and experimental demonstration of plasmonic Bragg filters and resonators inside metal-insulator-metal (MIM) waveguides. The presented filters and resonators are fabricated using standard top down lithography methods. The optical bandgap of the integrated Bragg filters is experimentally observed and its optical properties are investigated as a function of the grating pitch and the number of grating periods. Transmission filters based on a nanocavity resonance were measured, obtaining Q-factors above 30. Tuning of the cavity wavelength was experimentally achieved by varying the cavity length.

Plasmon filters and resonators in metal-insulator-metal waveguides

A near-infrared plasmonic refractive index (RI) sensor with figure of merit (FOM) as high as 124.6 is proposed and investigated numerically. The RI sensing is realized by employing the linear relation between resonant wavelength and RI of the material under detecting. Based on the fillet cavity coupled with two metal-insulator-metal waveguides, transmission efficiency (T) and optical resolution (FWHM) of the RI sensor are both improved to a great extent with T = 95% and FWHM = 12nm, keeping acceptable wavelength sensitivity of 1496nm/RIU within the near-infrared region. In addition, a sensitivity as high as 3476nm/RIU is obtained by optimizing the shape and size of fillet cavity. In general, the high FOM, transmittance and sensitivity achieved by our design may get further applications in biomedical science and nanophotonic circuits.

Numerical analysis of a near-infrared plasmonic refractive index sensor with high figure of merit based on a fillet cavity.

https://orbit.dtu.dk/files/10189552/81FF1d01.pdf

Plasmonic modulator optimized by patterning of active layer and tuning permittivity

We present a new metal-insulator-metal (MIM)-based plasmonic Bragg reflector (PBR) design that solves the technical problems of conventional step profile MIM PBRs through the use of sawtooth profiles. Our numerical study revealed that the sawtooth PBRs exhibit lower insertion loss, narrower bandgap, and reduced rippling in the transmission spectrum when compared with the step PBRs. The defect mode of the sawtooth PBR also exhibits a higher transmission, narrower linewidth, and higher Q-factor.

Characteristics of plasmonic Bragg reflectors with insulator width modulated in sawtooth profiles

As a solution to enhance the coupling between the surface plasmon-polariton (SPP) and optical waves propagating along dielectric waveguides, we present the finite thickness metal-insulator-metal (f-MIM) structure. Achieving such opto-plasmonic coupling has been difficult due to the inherent difference in the two waves’ dispersion characteristics. The f-MIM provides an effective way to tune the dispersion characteristics of its SPP mode to match those of the waveguide modes. The resultant enhancement in mode coupling enables waveguide-based excitation of SPPs, which, in turn, leads to the realization of integrated optic surface plasmon resonance (SPR) sensors. Our simulations showed that the effective index of the f-MIM's SPP mode can be increased to match those of typical dielectric waveguide modes even when the f-MIM itself was surrounded by low-index material such as water ( n  = 1.33). Moreover, the SPP's mode profile can also be controlled simultaneously to exhibit its peak at the interface with the analyte. All these characteristics render the f-MIM an ideal element for waveguide-based SPR sensing in aqueous environment. By integrating the f-MIM with a polymer waveguide, we obtained SPR sensing resolutions of 1.53 × 10 −5 in RIU and 0.016 nm in thickness in refractometric and affinity sensing modes, respectively.

Numerical investigation of finite thickness metal-insulator-metal structure for waveguide-based surface plasmon resonance biosensing

We present a new nanoscale modulation scheme based on the formation of a plasmonic Young interference pattern and its collection by an excitation field pattern-sensitive metal–insulator–metal (MIM) waveguide. Our numerical investigations reveal that such a scheme can generate sensitive and quasi-linear changes in the output power level in response to the relative phase difference between the waves in the two Young interferometer branches. Thanks to the asymmetric positioning of the collector waveguide, the response becomes most sensitive and linear when the relative phase difference is close to zero. Such a response characteristic can benefit future plasmonic systems by eliminating the need for phase prebiasing. The strong interactions between the surface plasmon polaritons inside the MIM structures are also utilized for realizing functionalities beyond modulation, such as on/off modulation contrast enhancement and all-plasmonic and logic operation.

Plasmonic modulation and switching via combined utilization of Young interference and metal–insulator–metal waveguide coupling

We report the design and experimental realization of an organic photovoltaic device structure that can trap incident light in all polarization states without relying on two-dimensional, short-pitch ( 1000 nm) gratings and achieved the polarization diversity through balanced allocation of the plasmonic and guided mode-based light trapping routes to different polarization states. The experimental results showed strong enhancements in light absorption in all polarization states that would translate into a 15%–25% increase in the power conversion efficiency.

Polarization-diverse light absorption enhancement in organic photovoltaic structures with one-dimensional, long-pitch metallic gratings: Design and experiment

We numerically investigated the impact of long-pitch (>800 nm) metallic gratings on the absorption enhancement in thin-film photovoltaic devices. We found that gratings with such a long pitch can simultaneously enhance the absorption of TM- and TE-polarized sunlight by inducing lateral Fabry–Perot resonances of surface plasmon-polaritons and guided modes at the same time. The grating duty cycle turned out to be the most important factor in realizing the two enhancement effects in the same spectral regime. Especially for the TM light, the combined effect of long grating pitch and duty-cycle adjustment led to the formation of three plasmonic resonances that simultaneously cover the ridge and groove surfaces. All of these produced a polarization-diverse absorption enhancement corresponding to a factor of 1.17–1.18 increase in the photocurrent over a wide range of the grating pitch.

Yifen Liu

Papers

Characteristics of plasmonic Bragg reflectors with insulator width modulated in sawtooth profiles

Numerical investigation of finite thickness metal-insulator-metal structure for waveguide-based surface plasmon resonance biosensing

Plasmonic modulation and switching via combined utilization of Young interference and metal–insulator–metal waveguide coupling

Polarization-diverse light absorption enhancement in organic photovoltaic structures with one-dimensional, long-pitch metallic gratings: Design and experiment

Polarization-diverse broadband absorption enhancement in thin-film photovoltaic devices using long-pitch metallic gratings