gil shalev
Ben-Gurion University of the Negev
Dr. Gil Shalev is a senior lecturer at the department of electrical engineering, Ben-Gurion University of the Negev, Israel. He received his bachelor and master degrees in physics at the Tel-Aviv University, and his Ph.D. in physical electronics in Tel- Aviv University. He held a postdoctoral fellowship at the Max Planck Institute for the Science of Light (Erlangen, Germany).Research interests are: Light trapping in arrays of subwavelength light concentrators Label-free and specific biosensing based on novel field-effect silicon devices Research methodologies include: Optoelectronic numerical simulations Device fabrication and electronic characterizationFar-field optical spectroscopy and near-field optical imaging Photovoltaic characterization
Introduction
Light trapping is about capturing photons from an incident electromagnetic wave in order to generate heat or electric current. Surface decoration with arrays of subwavelength structures was demonstrated to provide increase in light trapping (exceeding the Yablonovitch limit) and, hence, light absorption enhancement. We recently introduced the light-funnel (LF) array as an absorption enhancement technique for photovoltaic applications that is bio-inspired by the properties of the fovea centralis1. The fovea centralis is a closely-packed vertical array of inverted-cone photoreceptor cells located in the retina that is responsible for high acuity binocular vision under well-lit conditions. In this manner the functionality of the fovea centralis resembles that of a photovoltaic cell: both trap light efficiently under bright light conditions.
Methods
Fabrication of light-funnel arrays. Silicon wafers were patterned using nano-sphere lithography with Langmuir-Blodgett technique.
Numerical calculations. The optical and the electrical simulations were performed with Synopsys TCAD Sentaurus, Mountain View, CA, USA. The optical response of the system was calculated using finite-difference time-domain simulations. The Poisson and the Continuity equations were solved for each mesh vertex in conjunction with the respective carrier generation file. The modeling accounted for doping dependent Shockley-Read-Hall (SRH) recombination, Auger recombination, surface recombination, bandgap renormalization for degenerately doped silicon and doping dependent mobility.
Results and discussion
Figure 2 presents a numerical evaluation of LF-based solar cells with an underlying substrate. The enhancement of the relative absorption of LF-arrays compared with undecorated thin film and an optimized nanopillar array is evident. LF-based solar cell exhibits a power conversion efficiency that is 45% higher than that of an optimized nanopillar-based cell. We suggest that the enhanced light absorption of the LF-arrays is due to the coupled effect of light trapping inside the arrays combined with light concentration of each one of the LFs in the array (a single LF is actually a light-cone, a known non-imaging light concentrator). Fabrication of silicon light-funnel arrays using low-cost processing techniques is also demonstrated.
References
1. Shalev, G., Schmitt, S. W., Embrechts, H., Brönstrup, G. & Christiansen, S. Enhanced photovoltaics inspired by the fovea centralis. Sci. Rep. 5, 8570 (2015).
Photovoltaics and solar cells at nanoscale , Nanotechnology for environment and energy
