Fiona Beck

Tunable light trapping for solar cells using localized surface plasmons

Effective light management is imperative in maintaining high efficiencies as photovoltaic devices become thinner. We demonstrate a simple and effective method of enhancing light trapping in solar cells with thin absorber layers by tuning localized surface plasmons in arrays of Ag nanoparticles. By redshifting the surface plasmon resonances by up to 200 nm, through the modification of the local dielectric environment of the particles, we can increase the optical absorption in an underlying Si wafer fivefold at a wavelength of 1100 nm and enhance the external quantum efficiency of thin Si solar cells by a factor of 2.3 at this wavelength where transmission losses are prevalent. Additionally, by locating the nanoparticles on the rear of the solar cells, we can avoid absorption losses below the resonance wavelength due to interference effects, while still allowing long wavelength light to be coupled into the cell. Results from numerical simulations support the experimental findings and show that the fraction ...

Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells

The authors acknowledge the A. R. C. and NOW for research conducted at the FOM as a part of the Joint Solar Programme for financial support.

Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells

We show experimentally that there is asymmetry in photocurrent enhancement by Ag nanoparticle arrays located on the front or on the rear of solar cells. The scattering cross-section calculated for front- and rear-located nanoparticles can differ by up to a factor of 3.7, but the coupling efficiency remains the same. We attribute this to differences in the electric field strength and show that the normalized scattering cross-section of a front-located nanoparticle varies from two to eight depending on the intensity of the driving field. In addition, the scattering cross-section of rear-located particles can be increased fourfold using ultrathin spacer layers.

Effective light trapping in polycrystalline silicon thin-film solar cells by means of rear localized surface plasmons

Significant photocurrent enhancement has been achieved for evaporated solid-phase-crystallized polycrystalline silicon thin-film solar cells on glass, due to light trapping provided by Ag nanoparticles located on the rear silicon surface of the cells. This configuration takes advantage of the high scattering cross-section and coupling efficiency of rear-located particles formed directly on the optically dense silicon layer. We report short-circuit current enhancement of 29% due to Ag nanoparticles, increasing to 38% when combined with a detached back surface reflector. Compared to conventional light trapping schemes for these cells, this method achieves 1/3 higher short-circuit current.

The effect of dielectric spacer thickness on surface plasmon enhanced solar cells for front and rear side depositions

K.R.C. acknowledges the support of an Australian Research Council fellowship and the EU FP7 PRIMA project.

Resonant SPP modes supported by discrete metal nanoparticles on high-index substrates

We provide a new physical interpretation of scattering from plasmonic nanoparticles on high-index substrates. We demonstrate the excitation of different types of resonant modes on disk-shaped, Ag nanoparticles. At short wavelengths, the resonances are localised at the top of the particle, while at longer wavelengths they are localised at the Ag/substrate interface. We attribute the long wavelength resonances to geometric resonances of surface plasmon polaritons (SPPs) at the Ag/substrate interface. We show that particles that support resonant SPP modes have enhanced scattering cross-sections when placed directly on a high-index substrate; up to 7.5 times larger than that of a dipole scatterer with an equivalent free-space resonance. This has implications for designing scattering nanostructures for light trapping solar cells.

Light trapping with plasmonic particles: beyond the dipole model

Disk-shaped metal nanoparticles on high-index substrates can support resonant surface plasmon polariton (SPP) modes at the interface between the particle and the substrate. We demonstrate that this new conceptual model of nanoparticle scattering allows clear predictive abilities, beyond the dipole model. As would be expected from the nature of the mode, the SPP resonance is very sensitive to the area in contact with the substrate, and insensitive to particle height. We can employ this new understanding to minimise mode out-coupling and Ohmic losses in the particles. Taking into account optical losses due to parasitic absorption and outcoupling of scattered light, we estimate that an optimal array of nanoparticles on a 2 μm Si substrate can provide up to 71% of the enhancement in absorption achievable with an ideal Lambertian rear-reflector. This result compares to an estimate of 67% for conventional pyramid-type light trapping schemes.

Resonant nano-antennas for light trapping in plasmonic solar cells

We investigate the influence of nanoparticle height on light trapping in thin-film solar cells covered with metal nanoparticles. We show that in taller nanoparticles the scattering cross-section is enhanced by resonant excitation of plasmonic standing waves. Tall nanoparticles have higher coupling efficiency when placed on the illuminated surface of the cell than on the rear of the cell due to their forward scattering nature. One of the major factors affecting the coupling efficiency of these particles is the phase shift of surface plasmon polaritons propagating along the nanoparticle due to reflection from the Ag/Si or Ag/air interface. The high scattering cross-sections of tall nanoparticles on the illuminated surface of the cell could be exploited for efficient light trapping by modifying the coupling efficiency of nanoparticles by engineering this phase shift. We demonstrate that the path length enhancement (with a nanoparticle of height 500 nm) at an incident wavelength of 700 nm can be increased from ~6 to ~16 by modifying the phase shift at the Ag/air interface by coating the surface of the nanoparticle with a layer of Si.

Plasmonic light trapping leads to responsivity increase in colloidal quantum dot photodetectors

We report broadband responsivity enhancement in PbScolloidalquantum dot (CQDs) photoconductive photodetectors due to absorption increase offered by a plasmonicscattering layer of Ag metal nanoparticles. Responsivity enhancements are observed in the near infrared with a maximum 2.4-fold increase near the absorption band edge of ∼1 μm for ∼400 nm thick devices. Additionally, we study the effect of the mode structure on the efficiency of light trapping provided by random nanoparticlescattering in CQD films and provide insights for plasmonicscattering enhancement in CQD thin films.

Combined plasmonic and dielectric rear reflectors for enhanced photocurrent in solar cells

To reduce the use of fossil fuels and to fulfill the increasing energy demand for the fast growing population of our planet, renewable energies need to be more efficient and cheaper. A way of reducing the silicon solar cell cost for today’s technology is by using thinner layers and therefore less of the silicon material that accounts for about 50% of the photovoltaic module cost. However, due to weak absorption of infrared light in crystalline Si (c-Si), a significant fraction of solar energy is not converted into electricity in thin-film devices. Proper light management can potentially lead to ultra-efficient thin solar cells. 1 One method of achieving absorption enhancement in thin-film solar cells is through the excitation of localized surface plasmons in metal nanoparticles. These can be used as subwavelength scattering elements to couple a large fraction of incident light into trapped modes within a nearby semiconductor layer. 2‐10