Tunable light trapping for solar cells using localized surface plasmons

Abstract

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 of light backscattered into the cell by nanoparticles located on the rear is comparable to the forward scattering effects of particles on the front. Using nanoparticle self-assembly methods and dielectrics commonly used in photovoltaic fabrication this technology is relevant for application to large-scale photovoltaic devices.

Nanoplasmonics: a frontier of photovoltaic solar cells

“…This disadvantage generally exists for any sub-wavelength light trapping mechanism and it has to be overcome [7,32] . Based on these design principles, numerous computational and experimental studies have been reported on tuning the metal material, the shape, size and packing density, the dielectric environment and the position of the plasmonic nanostructures in PV devices to achieve enhanced light absorption for various types of solar cells [10,13,15,24,[31][32][33][34][35][36][37][38] .…”

Plasmas meet plasmonics

“…By using relatively large Ag islands (around 50 nm) the scattering of light into the PV cell is enhanced, the plasmon resonance of these particles can be tuned so it is around the desired wavelength by modifying the surrounding local dielectric environment [179]. Note that the enhancement may be optimised by varying the shape, size, material and surface coverage of the nanostructure [178][179][180][181][182][183][184]. Figure 6a shows that higher aspect nanostructures (i.e., cylinders rather than spheres) maximises the fraction of incident light scattered into the photoactive layer and hence enhances the solar cell efficiency [180].…”

“…Recall Section 3, in particular equations (16) and (17) which showed that scattering dominates in larger particles whereas absorbance is more important for smaller particles. By using relatively large Ag islands (around 50 nm) the scattering of light into the PV cell is enhanced, the plasmon resonance of these particles can be tuned so it is around the desired wavelength by modifying the surrounding local dielectric environment [179]. Note that the enhancement may be optimised by varying the shape, size, material and surface coverage of the nanostructure [178][179][180][181][182][183][184].…”

“…Methods to construct nanostructure arrays suitable for this purpose include fragmentation after thermal evaporation [179], as well as plasma-assisted nanosphere lithography [127] and plasma-assisted deposition through nanopore arrays [125,126] discussed in Section 4.2. The benefit there is that the size of the nanoparticles in template-based methods is more controllable than in stress-induced fragmentation [186] which results in a very broad island size distribution.…”

Improved efficiency of thin film a-Si:H solar cells with Au nanoparticles

“…More recently, nanotechnology has been used with plasmonic light trapping of metal nanoparticles (NP) like gold (Au) or silver (Ag) [3][4][5]. For incorporating metal NPs into solar cells, different methods have been established that includes island annealing and colloidal metal particles [6][7]. Also, some numerical models have been developed to understand the plasmonic effect [8].…”