The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for improved photovoltaic devices

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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Photoinduced reactivity of titanium dioxide

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

The ability to control the size, shape, and material of a surface has reinvigorated the field of surface-enhanced Raman spectroscopy (SERS). Because excitation of the localized surface plasmon resonance of a nanostructured surface or nanoparticle lies at the heart of SERS, the ability to reliably control the surface characteristics has taken SERS from an interesting surface phenomenon to a rapidly developing analytical tool. This article first explains many fundamental features of SERS and then describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates. In particular, we review metal film over nanosphere surfaces as excellent candidates for several experiments that were once impossible with more primitive SERS substrates (e.g., metal island films). The article also describes progress in applying SERS to the detection of chemical warfare agents and several biological molecules.

Surface-Enhanced Raman Spectroscopy

Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle layers were fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase in optical electrical field inside the photoactive layer, the inclusion of such particle films lead to increased optical absorption and consequently increased photoconversion at solar-conversion relevant wavelengths. The resulting solar energy conversion efficiency for a bulk heterojunction photovoltaic device of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester was found to increase from 1.3%±0.2% to 2.2%±0.1% for devices employing thin plasmon-active layers. Based on six measurements, the improvement factor of 1.7 was demonstrated to be statistically significant.

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

Temporal fluctuations in the Raman spectrum from molecules adsorbed to noble metal colloids (i.e., “blinking”) has been viewed as a single molecule signature. It is demonstrated here that silver colloids exhibit blinking that is independent of the nature of the adsorbate. Blinking was observed on silver colloids in the presence and absence of a SERS probe (e.g., R6G, BPE), sodium chloride, poly-l-lysine, an alkanethiol layer, and a liquid overlayer (e.g., water, methanol). These observations suggest that the mechanism that gives rise to blinking is insensitive to the nature of the adsorbate and is likely to be a property of the nanoparticle. Consistent with this idea, blinking was observed from vapor-deposited silver films and silver powders with no added molecular probe. In addition, two distinct broad luminescence-like (continuum) features also exhibited blinking and spectral diffusion, with no apparent adsorbate dependence. Evidence that SERS and the underlying continuum are associated is provided by a...

Flashy Silver Nanoparticles

Adhesive forces measured with an atomic force microscope under ambient conditions are generally regarded to be dominated by non-surface-specific capillary force. In this study, the nature of the “pull-off” force on a variety of surfaces was investigated as a function of relative humidity. The results indicate that even under the condition where capillary condensation occurs there is chemical specificity in the measured pull-off force. Issues such as tip−surface contact time and surface roughness were ruled out as possible artifacts. A mathematical model of pull-off force as a function of relative humidity is proposed in which the chemical specificity is explained.

Adhesion Forces Measured by Atomic Force Microscopy in Humid Air

Random silver nanohole films were created through colloidal lithography techniques and metal vapor deposition. The transparent electrodes were characterized by uv-visible spectroscopy and incorporated into an organic solar cell. The test cells were evaluated for solar power-conversion efficiency and incident photon-to-current conversion efficiency. The incident photon-to-current conversion efficiency spectra displayed evidence that a nanohole film with 92nm diameter holes induces surface-plasmon-enhanced photoconversion. The nanohole silver films demonstrate a promising route to removing the indium tin oxide transparent electrode that is ubiquitous in organic optoelectronics.

Kathy L. Rowlen

Papers

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

Flashy Silver Nanoparticles

Adhesion Forces Measured by Atomic Force Microscopy in Humid Air

Surface-plasmon enhanced transparent electrodes in organic photovoltaics

An SHG Magic Angle: Dependence of Second Harmonic Generation Orientation Measurements on the Width of the Orientation Distribution