Optics Communications 459 (2020) 125059 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom High absorption enhancement of invert funnel and conical nanowire solar cells with forward scattering Zoheir Kordrostami ∗ , Ali Yadollahi Department of Electrical and Electronic Engineering, Shiraz University of Technology, Shiraz, Iran ARTICLE INFO Keywords: Solar cell Nanowire Absorption enhancement Forward scattering ABSTRACT Silicon nanowire solar cells with enhanced absorptions have been designed. Engineering of the nanowire shapes have been used to increase the light trapping. The absorption enhancement of the cylindrical, conical, invert conical, funnel and invert funnel shaped nanowires have been studied and compared. Simulation results revealed that the invert funnel shaped nanowires has the best light trapping capability. Forward (Mie) scatterers have been added to the solar cells in the ITO top contact. The ITO scatterers appear like hemispheres which protrude from the top contact. Each nanowire is equipped with one hemispherical Mie scatterer on its top. The absorptions, percentages of the absorption enhancement, short circuit currents and power conversion efficiencies for all the proposed nanowire arrays before and after adding ITO scatterers have been computed and compared. The sizes of the Mie hemispheres have been chosen so that the short circuit current would be maximum. A significant enhancement in the absorption of all the solar cells with different nanowire shapes were realized due to the forward scattering. Among all the studied structures, some nanowire designs could reach short circuit currents of more than of 32 mA/cm 2 more than 52% absorption enhancements with respect to the simple cylindrical nanowires and more than 18% power conversion efficiencies. The simulation findings give the experimental researchers guidance on how to optimize the nanostructures to further improve the solar cell performance. 1. Introduction It seems that nanotechnology might be the only recourse that can reduce both cost and size and increase the efficiency in photovoltaics. During recent years, semiconductor nanostructures have been investi- gated as the structure blocks for next-generation optoelectronic devices. One of the most interesting strategies for improving the collection of the solar radiation and increasing the light trapping ability of solar cells is to use nanostructures [1]. Nanostructuring the solar cells by using surface-grown nanoparticles [2,3], nanorods [4–6], nanowires [7,8], other nanostructures [9,10] and nanoholes [11] have recently been studied with the goal of achieving more absorptions in a wider fre- quency range [12]. The studies on nanowires started by some important works which would shine light on the underlying optics of nanowires optical response [13–15]. The most important benefit of the semicon- ductor nanowires which results in significant enhancement in carrier collection efficiency is their ability in light trapping which is to collect the photo-generated carriers in a short length. In a traditional solar cell, the active layer must be thick enough to have adequate light absorption and at the same time must provide long diffusion lengths to collect the exited carriers. All the nanoscale arrays behave as ideal light absorbers which can optimize the optical path length of incident ∗ Corresponding author. E-mail address: kordrostami@sutech.ac.ir (Z. Kordrostami). light and minimize the escape from the surface. Silicon nanowire design can satisfy both criteria. Nanowires provide long path for light absorption and a perpendicular short pathway for carrier collection. Other key advantages of nanowires lie in the reduced cost of the solar cell due to less silicon volume fraction and the possibility of growth on different materials such as low-cost or flexible substrates without severe requirements of lattice matching. In large scale processing, free lattice matching provides much cheaper and better substrates for growth of silicon nanowires. It has been previously proved that the light absorption of nanowires is more than a thin-film with identical amount of material [7]. It is predicted that by emerging new designs for nanostructured solar cells, their relatively small efficiencies will shortly surpass the values for the conventional solar cells [16]. The geometry dependent absorption characteristics of the nanowires have been studied previously and a large number of studies focus on managing the shape of the silicon nanowires such as cylinder, conic, etc. [12,17]. Today, many methods are being used to enhance the absorption of the solar cells like utilizing nanowires with different shapes [18], combination of grating and nanorods [19], core–shell structures [20,21], hybrid approaches [22,23], quantum dots [24– 26], plasmonic effects [27,28], surface texturing [29,30] and tandem https://doi.org/10.1016/j.optcom.2019.125059 Received 30 May 2019; Received in revised form 31 October 2019; Accepted 2 December 2019 Available online 4 December 2019 0030-4018/© 2019 Elsevier B.V. All rights reserved.