Supriya Pillai

Surface plasmon enhanced silicon solar cells

S. Pillai would like to acknowledge the UNSW Faculty of Engineering Research Scholarship. K.R. Catchpole acknowledges the support of an Australian Research Council fellowship.

Enhanced emission from Si-based light-emitting diodes using surface plasmons

The Centre of Excellence for Advanced Silicon Photovoltaics and Photonics is supported under the Australian Research Council’s Centres of Excellence Scheme.

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.

Absorption enhancement due to scattering by dipoles into silicon waveguides

One of the authors K.R.C. acknowledges the support of an Australian Research Council fellowship. The authors acknowledge the support of the Centre of Excellence for Advanced Silicon Photovoltaics and Photonics, supported by the Australian Research Council.

Realistic Silver Optical Constants for Plasmonics.

Silver remains the preferred conductor for optical and near-infrared plasmonics. Many high-profile studies focus exclusively on performance simulation in such applications. Almost invariably, these use silver optical data either from Palik’s 1985 handbook or, more frequently, an earlier Johnson and Christy (J&C) tabulation. These data are inconsistent, making it difficult to ascertain the reliability of the simulations. The inconsistency stems from challenges in measuring representative properties of pristine silver, due to tarnishing on air exposure. We demonstrate techniques, including use of silicon-nitride membranes, to access the full capabilities of multiple-angle, spectrometric-ellipsometry to generate an improved data set, representative of overlayer-protected, freshly-deposited silver films on silicon-nitride and glass.

Re-evaluation of literature values of silver optical constants

Silver has unique optical properties for topical applications such as plasmonics. The two most widely used silver optical data sets are the Palik handbook compilation and that determined by Johnson and Christy. Unfortunately these are inconsistent making realistic modelling of the likely performance of silver in optical applications difficult, with modelling producing either highly optimistic or very pessimistic results, depending on application. By critical examination and duplication of the original experiments leading to the widely accepted literature values, we show that both data sets have drawbacks and conclude that there is a need for an improved data set for realistic simulation of experimentally obtainable properties.

Can plasmonic Al nanoparticles improve absorption in triple junction solar cells

Plasmonic nanoparticles located on the illuminated surface of a solar cell can perform the function of an antireflection layer, as well as a scattering layer, facilitating light-trapping. Al nanoparticles have recently been proposed to aid photocurrent enhancements in GaAs photodiodes in the wavelength region of 400–900 nm by mitigating any parasitic absorption losses. Because this spectral region corresponds to the top and middle sub-cell of a typical GaInP/GaInAs/Ge triple junction solar cell, in this work, we investigated the potential of similar periodic Al nanoparticles placed on top of a thin SiO2 spacer layer that can also serve as an antireflection coating at larger thicknesses. The particle period, diameter and the thickness of the oxide layers were optimised for the sub-cells using simulations to achieve the lowest reflection and maximum external quantum efficiencies. Our results highlight the importance of proper reference comparison, and unlike previously published results, raise doubts regarding the effectiveness of Al plasmonic nanoparticles as a suitable front-side scattering medium for broadband efficiency enhancements when compared to standard single-layer antireflection coatings. However, by embedding the nanoparticles within the dielectric layer, they have the potential to perform better than an antireflection layer and provide enhanced response from both the sub-cells.

Design of Anodic Aluminum Oxide Rear Surface Plasmonic Heterostructures for Light Trapping in Thin Silicon Solar Cells

A metal-dielectric heterostructure that provides the combined capability of light trapping and surface passivation is reported. The light-trapping layer employs a porous aluminum anodic oxide (AAO) with metal nanoparticles formed in the pores on the rear surface of a thin crystalline silicon solar cell. Numerical finite-difference time domain (FDTD) simulations were performed to determine the pore diameter and spacing that would result in optimal light trapping for this metal-dielectric heterostructure. For a 2.5-μm-thick crystalline silicon device, the optimal pore diameter and spacing were determined to be ~250 and ~450 nm, respectively. These conditions resulted in an enhancement of the simulated photocurrent by ~12.6% compared with a device in which the heterostructure was replaced with a homogenous aluminum oxide layer. Simulations also confirmed that the thickness of an underlying dielectric layer should be minimized to 10-20 nm, with the AAO barrier layer being maintained as thin as possible. Finally, it was shown that replacement of silver by aluminum in the pores resulted in a reduction in the photocurrent of 6.3% and would necessitate much larger pore spacing that is difficult to achieve experimentally and would result in thicker AAO barrier layers, which are undesirable.

Enhanced Broadband Light Trapping in c-Si Solar Cells Using Nanosphere-Embedded Metallic Grating Structure

A hexagonal nanosphere (NS)-embedded back plasmonic grating structure is proposed to improve the light absorption of crystalline silicon (c-Si) solar cells. These structures are simple, can be deposited toward the final stages of device processing, and involve no increase in the surface area of the semiconductor layer. Experimental fabrication of this structure on a 200-μm c-Si wafer has been realized using silver, resulting in broadband absorption enhancement in the near-infrared region. In corresponding to the optical measurement, a maximum potential photocurrent density enhancement of around 2.23 mA/cm2 has been predicted, compared with the reference with a planar metal reflector. Three-dimensional finite-element method numerical simulations were also performed on smooth and irregular surface geometries of the NSs. Our results demonstrate that while both configurations perform better than a planar reflector, the irregular nanofeatures on the gratings can adjust the optical resonance to ensure that the light is more efficiently scattered into the Si, which would significantly improve its optical absorption. These structures have the potential to be used as rear metal contacts, in addition to performing the function of a light-trapping layer without increasing the fraction of the metal component.