Plasmonic enhancement of amorphous silicon solar photovoltaic cells with hexagonal silver arrays made with nanosphere lithography

Abstract

Nanosphere lithography (NSL) provides an opportunity for a low-cost and scalable method to optically engineer solar photovoltaic (PV) cells. For PV application, NSL is widely used in rear contact scenarios to excite SPP and/or high order diffractions, however, the top contact scenarios using NSL are rare. In this paper a systematic simulation study is conducted to determine the capability of achieving efficiency enhancement in hydrogenated amorphous silicon (a-Si:H) solar cells using NSL as a top contact plasmonic optical enhancer. The study focuses on triangular prism and sphere arrays as they are the most commonly and easily acquired through direct deposition or low-temperature annealing, respectively. For optical enhancement, a characteristic absorption profile is generated and analyzed to determine the effects of size, shape and spacing of plasmonic structures compared to an un-enhanced reference cell. The factors affecting NSLenhanced PV performance include absorption, shielding effects, diffraction, and scattering. In the triangular prism array, parasitic absorption of the silver particles proves to be problematic, and although it can be alleviated by increasing the particle spacing, no useful enhancement was observed in the triangular prism arrays that were simulated. Sphere arrays, on the other hand, have broad scattering cross-sections that create useful scattering fields at several sizes and spacing intervals. For the simulated sphere arrays the highest enhancement found was 7.4%, which was fabricated with a 250nm radius nanosphere and a 50nm silver thickness, followed by annealing in inert gas. These results are promising and provide a path towards the commercialization of plasmonic a-Si:H solar cells using NSL fabrication techniques.

Enhancement of hydrogenated amorphous silicon solar cells with front-surface hexagonal plasmonic arrays from nanoscale lithography

“…In previous work [31] , the simulation is carried out using COMSOL Multiphysics 5.1 commercial software package, which is based on the finite element methods (FEM). Having defined the dielectric functions and geometric parameters for each layer, the method was used to solve the frequency domain form of Maxwell's equations in three dimensions in a constrained range of the solar spectrum where a-Si:H is active (300nm to 750nm).…”

“…Under the given simulation settings, all the major optical processes including but not limited to scattering [13] , diffraction [19] , Fabry-Perot resonances [18] , and waveguide modes [37][38][39] that can play roles in the optical enhancement are automatically considered in the COMSOL simulations since Maxwell's equations accurately describe those processes in three dimensions. The further details of the simulation are described in reference [31] . Optical enhancement for each simulated cell is acquired by integrating the product of absorption rate and AM1.5 irradiance spectrum over the wavelength region of interest.…”

“…Nanosphere lithography (NSL) has progressed significantly and is promising to overcome this cost challenge [30] . NSL in combination with vertical evaporation tools creates a hexagonal array made of curved triangles, the dimension and spacing of the triangle can be controlled continuously by the nanosphere with diameter D used in NSL [31] . To achieve a uniformly patterned nanosphere monolayer with less defects, spin coating and interface coating provide high yield and produce colloidal mask of high mechanical strength [32] .…”

“…In this study the interface coating is used to fabricate the nanosphere monolayer as it is substrate independent with an anion surfactant, sodium dodecyl sulfate (SDS), which releases the surface tension and glue together the nanospheres [32] . In addition, a systematic simulation study has been completed to identify the fabrication parameters that maximize the enhancement using triangle or sphere hexagonal array [31] . The results show that the sphere array yield up to 7.4% optical enhancement using nanosphere radius of 250nm and silver film thickness of 50nm.…”

“…NSL is implemented using polystyrene nanosphere with interface coating as described in detail in Zhang et al [32] . In reference [31] , the simulation results for optical enhancement were presented for different geometric parameters with nanosphere radius ranging from 150nm to 500nm and the silver film thickness ranging from 25nm to 200nm. Considering those parameter sets, two types of nanospheres were selected in this work for the fabrication and testing with radius of 250nm and 500nm that are predicted to provide optical enhancement in [31] .…”