Photonic crystals with a continuous, Gaussian-type surface profile for near-perfect light trapping

Abstract

We show a unique design of teepee-like photonic crystal (TP-PC) structure that possesses a true gradient, Gaussian-type surface profile for smooth and accurate index matching between air and silicon for near-perfect light trapping. Such funnel-like, inverse-conical topography is capable of achieving near-zero optical reflection and near-unity solar absorption with excellent angular response over the entire visible light wavelength range. The fabrication only requires standard microelectronics reactive-ion etching (RIE) process. We demonstrate how various process parameters, such as RIE gas mixture ratio, RIE power, thickness of silicon dioxide (SiO 2 ) coatings, and lattice constant of the photonic crystal, can impact the details of the "Gaussian" profile and further improve the optical performance of the TP-PC structure at broad-λ, broad-θ, especially in the ultraviolet (UV) wavelength range. Our finite-difference time-domain (FDTD) simulation of the TP-PC structure reveals existence of multiple absorption resonances in the 800-to1100-nm wavelength range. Poynting vector plots show that such strong absorption enhancements at the resonant frequencies are due to long-lifetime photonic modes arising from parallel-to-interface refraction of the incoming sunlight and formation of vortex-like energy flow pattern inside the TP-PC structure. Our design will lead the way for future development of ultrathin, high-efficiency c-Si solar photovoltaics.

Tunable Nanoporous Anodic Alumina Photonic Crystals by Gaussian Pulse Anodization

“…This model can be easily implemented to describe the effective medium of composite photonic crystal systems. In particular, the Looyenga–Landau–Lifshitz model adapted to NAA-GPCs can be expressed by eq − where n eff‑NAA‑GPCs 2/3 is the effective refractive index of NAA-GPCs, n Al 2 O 3 2/3 is the refractive index of alumina, f medium is the volume fraction of the filling medium, n medium 2/3 is the refractive index of the filling medium, and f Al 2 O 3 is the volume fraction of alumina.…”

“…The optical properties of Gaussian NAA-GPCs were modeled by combining an effective medium approximation (EMA) model and the transfer matrix method (TMM). The effective refractive index of each layer within NAA-GPCs’ structure was estimated by the Looyenga–Landau–Lifshitz (3L) EMA model in combination with that reported from Bartzsch , and Kuang …”

Photonic Crystal Structures for Photovoltaic Applications

“…[ 85 ]. Kuang et al [ 81 , 87 ] proposed a unique teepee-like PC on crystalline silicon (c-Si). This structure is characterized by excellent antireflection due to its Gaussian-type gradient index profile.…”