Nanoparticle‐enhanced light trapping in thin‐film silicon solar cells

Abstract

A systematic investigation of the nanoparticle-enhanced light trapping in thin-film silicon solar cells is reported. The nanoparticles are fabricated by annealing a thin Ag film on the cell surface. An optimisation roadmap for the plasmonenhanced light-trapping scheme for self-assembled Ag metal nanoparticles is presented, including a comparison of rearlocated and front-located nanoparticles, an optimisation of the precursor Ag film thickness, an investigation on different conditions of the nanoparticle dielectric environment and a combination of nanoparticles with other supplementary backsurface reflectors. Significant photocurrent enhancements have been achieved because of high scattering and coupling efficiency of the Ag nanoparticles into the silicon device. For the optimum light-trapping scheme, a short-circuit current enhancement of 27% due to Ag nanoparticles is achieved, increasing to 44% for a "nanoparticle/magnesium fluoride/ diffuse paint" back-surface reflector structure. This is 6% higher compared with our previously reported plasmonic shortcircuit current enhancement of 38%.

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] .…”

“…The bulk recombination is so high that the surface passivation is unnecessary, and the contact between metal and the active layer only results in benefi cial near-fi eld enhancement, and does not cause noticeable performance degradation. Take one such " low quality " material, the evaporated thin-fi lm polycrystalline Si for example, the light absorption and solar cell effi ciency tend to be signifi cantly improved when the dielectric spacing layer was reduced and fi nally removed, enabling near-fi eld enhancements [24,44] . Periodic metal nanostructures on the surface of a PV device can excite surface plasmon polariton (SPP) modes.…”

“…One popular suggestion is to mix multiple types of nanoparticles, with distinct resonances, over the device surface [24,38,46] . However, there is an obvious limit to this process in that geometrically each nanoparticle can only occupy one place on the surface.…”

“…2 The Ag nanostructure acts as plasmonic BSR, and it also causes uneven active layers of the cells, which also scatters the light. of the metal element and the structure volume can achieve a relatively large scattering cross section and a small absorption cross section, increasing the scattering/absorption ratio of the metal nanostructure [30,41] ; when the metal nanostructures are coated with dielectric materials, the absorption peak can shift away from the scattering peak to insignifi cant wavelengths, leaving the scattering peak at the important wavelengths for maximum light enhancement [42,43] ; rearlocated nanostructures in a PV device do not suffer from the dissipated absorption of the short wavelength light in the metal, as this range of light is absorbed by the solar cell active layer during the its fi rst pass through it [12,16,18,24,[36][37][38]44] ; we recently reported that by using a nanomaterial (such as Al) whose SPR wavelength is shorter than the lower end of the absorption band of the PV device, the metal absorption can be minimized and the forward scattering can still be mostly preserved [45] . For PV devices with heavily damped semiconductors, their active layers are able to compete with unwanted metal absorption.…”

“…In this method a metal thin-fi lm was deposited directly on the solar cell surface, followed by a thermal annealing process at about 200 ° C to transform the metal fi lm into nanoparticles. Reported deposition methods for plasmonic solar cells include thermal evaporation [10,12,16,20,24,34,79,80,81] , electron-beam evaporation [46] and sputtering [16] . With deposited fi lm thickness the same, evaporation and sputtering were found to produce identical nanoparticles [16] .…”