Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Front dielectric and back plasmonic wire grating for efcient light trapping in perovskite solar cells Omar A.M. Abdelraouf a,b , Ahmed Shaker b , Nageh K. Allam a,∗ a Energy Materials Laboratory (EML), Department of Physics, School of Sciences and Engineering, The American University in Cairo, New Cairo, 11835, Egypt b Department of Engineering Physics and Mathematics, Faculty of Engineering, Ain Shams University, Cairo, 11517, Egypt ARTICLEINFO Keywords: Plasmonic Dielectric Grating Nanostructures Light trapping Perovskite solar cells (PSCs) ABSTRACT Thin flm perovskite solar cells (PSCs) based on (CH 3 NH 3 PbI 3 ) have been emerged as good alternatives to conventional silicon solar cells due to their low cost, low fabrication temperature, high carrier collection ef- ciency, and high-power conversion efciency (PCE). However, the small thickness of thin flm solar cells limits lightabsorptioncomparedtothicksolarcells.Inthiswork,weproposedatheoreticaldesignforenhancinglight absorptiontoachievemaximumtheoreticalphotocurrentusingfrontdielectricandbackplasmonicwiregrating. Using fnite element method (FEM) three-dimensional optical model, the optimum size and periodicity of the studied wire grating nanostructures were identifed. Additionally, the electrical model revealed a satisfactory enhancement in PCE over that of the planar structure counterpart. The simulation results showed an average enhancement of 22.4% in total generation rate for the entire simulated wavelength, and more than 85% en- hancement in narrow-band wavelength compared to the planar structure counterpart. 1. Introduction Thirdgenerationthinflmsolarcells(TFSCs)haveemergedasgood alternatives for conventional solar cells. TFSCs have many advantages such as higher collection efciency, low cost of materials and fabrica- tion[1].Recently,manyresearchgroupsfocusonenhancingperovskite solar cells (PSCs), due to their very low cost of fabrication using solu- tion proceed spin coating and very high efciency over the second generation TFSCs [2]. However, TFSCs have limitation in absorbing longerwavelengthsofthelightspectrumduetotheirsmallactivelayer thickness.Inthisregard,lighttrappingnanostructuresarebeingusedto enhance light absorption inside many types of TFSCs [3,4]. However, fabrication of these large-scale uniform nanostructures is a challenging process. An alternative technique for enhancing light trapping in TFSCs is to use front grating plasmonic nanostructures [5]. In this technique, selectednanostructuresarerequiredtoreducelightlossesduetoOhmic losses in these top metallic nanostructures. High refractive index di- electric front grating nanostructures have been explored to overcome light absorption problems in plasmonic nanostructures [6,7]. However, light scattering due to Mie resonance results in high scattering cross- section comparable to plasmonic and increase coupling of smaller wa- velength light in the substrate. Also, fabrication of uniform plasmonic or dielectric front grating nanostructures is challenging. To this end, back contact wire grating was previously fabricated using roll-to-roll methodforenhancinglightabsorptionofa-Si:HTFSCs[8].Backgrating exhibits many advantages to guide higher wavelength light using lo- calized surface plasmon resonance (LSPR), or scattering light in high cross section, which results in increasing light absorption of larger wavelengths. On the other hand, front and back grating was recently reported for enhancing μc-Si:H TFSCs light trapping [9]. The separate optimization of front and back grating for maximum light absorption enhancementswasaddressed.However,thefabricationcostisstillvery high as the process includes multiple steps. Herein, we present a theoretical design for using dielectric front wire grating and plasmonic back wire grating. Our proposed design is based on the advantages of controlling the light scattering directivity using Mie resonance for front dielectric wire grating, while the plas- monic back wire grating would guide and confne light at sub- wavelengthusingLSPR.Thistheoreticalstudyappliestheseconceptson previously fabricated PSCs [10],andcomparetheenhancementinlight absorption. As the perovskite's active layer was fabricated via solution processedspincoating,thefrontgratingshapewouldcopytheshapeof the back grating after deposition. Thus, we could not apply separate optimization for front and back grating. Using coupled optical and electricalmodeling,westudiedtheefectofusingdiferentcrosssection wires grating and their periodicities and dimensions on light trapping inside perovskite's active layer. Results predict range of dimensions for simulated wires, to achieve maximum theoretical illuminating current. https://doi.org/10.1016/j.optmat.2018.10.028 Received 25 September 2018; Received in revised form 8 October 2018; Accepted 13 October 2018 ∗ Corresponding author. E-mail address: nageh.allam@aucegypt.edu (N.K. Allam). Optical Materials 86 (2018) 311–317 0925-3467/ © 2018 Elsevier B.V. All rights reserved. T