| Abstract Scope |
Photovoltaic technology based on thin silicon films is attractive as it reduces the bulk material costs of manufacture. Unfortunately, photon absorption in the near-infrared spectrum is very weak in silicon, thereby resulting in significant loss of potential photocurrent. Much research is therefore focused on advanced methods for trapping light in thin silicon films as an avenue for recovering this unused power. In our recent work, we explored a concept for optical absorption enhancement using embedded dielectric nanoparticles inside an infinite silicon half-space. The absorbed power in the top 1.0um of the silicon was increased by 6% based solely on excess path length of the first optical pass. In this work, we explore the effects of embedded nanoparticles in finite structures capable of waveguiding and non-trivial path-length enhancement. We first consider the influences of varying the geometric parameters relating to SiO2 nano-spheres embedded in a 1.0um layer of crystalline silicon sandwiched between a 75nm Si3N4 anti-reflective coating and an Al back contact. The layout for an embedded nanosphere is defined by a characteristic diameter D, depth z, and pitch p. Using numerical simulations based on the finite-difference time-domain method (FDTD), we explore the effects of varying each parameter by calculating the net absorption gain in incident solar photons within the active semiconductor layer. Under ideal conditions, absorption gains due to embedded spheres of SiO2 can reach as high as 23% relative to an identical geometry without the embedded nanoparticles. We also infer a series of design principles from our results that include trade-offs between light-trapping, displacement of active semiconductor material, out-coupling through the top surface, and silicon absorption at long wavelengths. Absorption gain may be further increased beyond 30% by embedding coated metallic spheres, which possess a stronger scattering efficiency in silicon than pure dielectrics. Using a tandem design based on crystalline and amorphous silicon, we also simulate the effects of surface texturing and embedded particles both in isolation and in combination. We then infer another series design principles based on advanced, hybrid approaches that attempt to maximize light-trapping in tandem cells. |