Simulations of solar cell absorption enhancement using resonant modes of a nanosphere array

We propose an approach for enhancing the absorption of thin-film amorphous silicon solar cells using periodic arrangements of resonant dielectric nanospheres deposited as a continuous film on top of a thin planar cell. We numerically demonstrate this enhancement using 3D full field finite difference time domain simulations and 3D finite element device physics simulations of a nanosphere array above a thin-film amorphous silicon solar cell structure featuring back reflector and anti-reflection coating. In addition, we use the full field finite difference time domain results as input to finite element device physics simulations to demonstrate that the enhanced absorption contributes to the current extracted from the device. We study the influence of a multi-sized array of spheres, compare spheres and domes and propose an analytical model based on the temporal coupled mode theory

Effects of bulk and grain boundary recombination on the efficiency of columnar-grained crystalline silicon film solar cells

Columnar-grained polycrystalline silicon films deposited at low temperatures are promising materials for use in thin-film photovoltaics. We study the effects of recombination at grain boundaries, bulk intragranular recombination, grain size, and doping in such structures with two-dimensional device physics simulations, explicitly modeling the full statistics and electrostatics of traps at the grain boundary. We characterize the transition from grain-boundary-limited to bulk-lifetime-limited performance as a function of intergranular defect density and find that higher bulk lifetimes amplify grain boundary recombination effects in the intermediate regime of this transition. However, longer bulk lifetimes ultimately yield higher efficiencies. Additionally, heavier base doping is found to make performance less sensitive to grain boundary defect density

Design of Nanostructured Solar Cells Using Coupled Optical and Electrical Modeling

Nanostructured light trapping has emerged as a promising route toward improved efficiency in solar cells. We use coupled optical and electrical modeling to guide optimization of such nanostructures. We study thin-film n-i-p a-Si:H devices and demonstrate that nanostructures can be tailored to minimize absorption in the doped a-Si:H, improving carrier collection efficiency. This suggests a method for device optimization in which optical design not only maximizes absorption, but also ensures resulting carriers are efficiently collected

Solar cell efficiency enhancement via light trapping in printable resonant dielectric nanosphere arrays

Resonant dielectric structures are a promising platform for addressing the key challenge of light trapping in thin-film solar cells. We experimentally and theoretically demonstrate efficiency enhancements in solar cells from dielectric nanosphere arrays. Two distinct amorphous silicon photovoltaic architectures were improved using this versatile light-trapping platform. In one structure, the colloidal monolayer couples light into the absorber in the near-field acting as a photonic crystal light-trapping element. In the other, it acts in the far-field as a graded index antireflection coating to further improve a cell which already included a state-of-the-art random light-trapping texture to achieve a conversion efficiency over 11%. For the near-field flat cell architecture, we directly fabricated the colloidal monolayer on the device through Langmuir–Blodgett deposition in a scalable process that does not degrade the active material. In addition, we present a novel transfer printing method, which utilizes chemical crosslinking of an optically thin adhesion layer to tether sphere arrays to the device surface. The minimally invasive processing conditions of this transfer method enable the application to a wide range of solar cells and other optoelectronic devices. False-color SEM image of an amorphous silicon solar cell with resonant spheres on top

Effect of defect-rich epitaxy on crystalline silicon / amorphous silicon heterojunction solar cells and the use of low-mobility layers to improve performance

We present two-dimensional device physics simulations of amorphous silicon / crystalline silicon heterojunction solar cells to explain the effects of full and localized epitaxial layers, sometimes observed in the early stages of amorphous Si deposition, on cell performance. Minimizing the defect density, thickness, and wafer area fraction covered by the epitaxial region are shown to be important factors for maximizing cell open circuit voltage. We find that localized defect-rich epitaxial patches covering small percentages of the wafer surface (~5%) can cause significant reduction in open circuit voltage, which is explained by considering lateral carrier flow in the device. We also show that a thin layer of low-mobility material, such as microcrystalline silicon, included between the wafer and amorphous regions can impede lateral carrier flow and improve conversion efficiencies in cases where isolated defective pinholes limit device performance

Effect of defect-rich epitaxy on crystalline silicon / amorphous silicon heterojunction solar cells and the use of low-mobility layers to improve performance

We present two-dimensional device physics simulations of amorphous silicon / crystalline silicon heterojunction solar cells to explain the effects of full and localized epitaxial layers, sometimes observed in the early stages of amorphous Si deposition, on cell performance. Minimizing the defect density, thickness, and wafer area fraction covered by the epitaxial region are shown to be important factors for maximizing cell open circuit voltage. We find that localized defect-rich epitaxial patches covering small percentages of the wafer surface (~5%) can cause significant reduction in open circuit voltage, which is explained by considering lateral carrier flow in the device. We also show that a thin layer of low-mobility material, such as microcrystalline silicon, included between the wafer and amorphous regions can impede lateral carrier flow and improve conversion efficiencies in cases where isolated defective pinholes limit device performance