Enhancing Solar Cell Efficiency with Plasmonic Behavior of Double Metal
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Vacuum 152 (2018) 285e290 Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum Enhancing solar cell efficiency with plasmonic behavior of double metal nanoparticle system * Nipon Deka a, Maidul Islam a, Prashant K. Sarswat b, , Gagan Kumar a a Department of Physics, Indian Institute of Technology Guwahati, Guwahati, 781039, India b Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT, 84112, USA article info abstract Article history: The use of special arrangement of silver nanoparticle (Ag Np) arrays is presented in order to enhance Received 20 November 2017 light trapping capability of the thin film solar cells due to their ability to couple incident sunlight into Received in revised form localized modes. The spatial distribution of the nanoparticles in the matrix and their relative position are 10 March 2018 the important factors governing the performance of the device. Double nanoparticle system (DNS) over Accepted 19 March 2018 the silicon substrate, which is not a commonly studied system, is explored and the performance (ab- Available online 20 March 2018 sorption enhancement) was compared with periodically arranged single Ag Nps system. Finite difference time domain (FDTD) simulation has been performed to investigate the effect of silver nanoparticle array patterning on the absorption of solar radiation. The presence of DNS was found responsible for increased coupling of photons into plasmonic modes, and consequently increased absorption of photons into the substrate over a broad range of the solar spectrum. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction plasmonic nanostructures have the capability to enhance absorp- tion near the localized plasmon resonance, which in turn resulted In the last and recent decade, researchers have paid keen overall power conversion enhancement. Hence, plasmonic solar attention to solar cell technology as important and strategic cell based research is one of the hot and demanding field of interest research area [1e4]. The salient features of the photovoltaic science in recent decades. In 2005, Tian et al. reported their seminal work and technology and associated motivation of the research in this on the conversion of the photocurrent from absorbed visible light segment are due to low-maintenance, cost-effective, clean, and by metal nanoparticles [11]. It was observed that plasmonically environment-friendly nature of this technology. Furthermore, solar induced gold particles incorporated in a TiO2 matrix [12] can cause cells are long lasting sources of energy which are renewable and the charge separation and efficient conversion of photocurrent can provide sustainable power. To increase the conversion effi- resulting from the absorbance spectra of AueTiO2 films was ciency of the solar cell to the photocurrent, one needs structure claimed. Later on, in year 2008, enhancements of photocurrent in which has high absorption. In this regard, metal nanoparticles have GaAs solar cells using Ag nanoparticles was reported [13]. In their very high absorption and scattering cross-section features which research, plasmonic effect for the absorption and resulting photo- are very useful for solar cells, depending upon their size and shape current change for the different size/shape of Ag nanoparticles [5,6]. Optical properties of plasmonic [7] nanoparticles strongly (from hemispheres to cones while increasing the height) was depend on their size and shapes therefore appropriate size and investigated. In later years, Munday et al. proposed integrated ab- shape are crucial parameters to achieve a highly efficient solar cell. sorption enhancement from the combination of the metallic grat- There are several ways to insert metal nanoparticles (MNP) in ings and an antireflection (AR) coating [14]. It was observed that a solar cell absorber layers [2,8e10]. The relative position and combination of gratings and traditional AR coatings can exceed the orientation of the nanoparticles in solar cell are important pa- absorption enhancement rather than either metallic gratings or AR rameters determining the solar cell performance. Metal based coatings. Scattering efficiency and absorption losses are the crucial factors in the case of metal nanoparticles based solar cells applications. In the starting of current decade, it was shown that among the metal * Corresponding author. 135 S, 1460 E, Room 412, Salt Lake city, UT, 84112, USA. nanoparticles, silver is highly efficient for the scattering and E-mail address: [email protected] (P.K. Sarswat). https://doi.org/10.1016/j.vacuum.2018.03.026 0042-207X/© 2018 Elsevier Ltd. All rights reserved. 286 N. Deka et al. / Vacuum 152 (2018) 285e290 absorption, mainly due to its large scattering efficiency and low DNS is denoted by 0p0 and the diameter of each metallic nano- absorption losses. These MNPs have offered greatest efficiency particle is denoted by 0d0. The internal gap between the two metallic 0 improvements in the variety of solar cells [15,16]. In 2012, Reineck nanoparticles in the DNS is 0i : Two major analysis are performed et al. reported the generation of photocurrents in a solid state de- where the absorption enhancement is determined by varying the vice, comprised of spherical silver and gold nanoparticles deposited periodicity of the DNS and by varying the internal gap within the on TiO2ecoated substrate [17]. It was observed that incident photon DNS at different values of the diameter ‘d’ of the metallic nano- to electron conversion efficiency (IPCE), absorptivity, and current particles. The diameters that we considered were 0 density for Au nanoparticles were higher than that of Ag 0d ¼ 75 nm; 100 nm and 150 nm: Field monitors were placed on nanoparticles. the surface of the substrate and 0:5 mm below the surface. Their The efficiency enhancement of PbS quantum dot/ZnO nanowire purpose is to calculate transmission of the incident radiation at solar cells, using plasmonic behavior of silver nanocubes, was also those regions to generate the absorption profile. The periodicity of 0 proposed in 2015 [18]. This research was based on efficiency the DNS was varied by considering 0p ¼ 350 nm; 400 nm; 450 nm; enhancement of solar cell by controlling the position and amount of and 500 nm ðcentre to centreÞ and the internal gap was varied by 0 Ag nanocubes in a large scale while PbS quantum dots exhibited considering 0i ¼ 5 nm; 10 nm; 15 nm; and 20 nm: The wavelength weak absorption without Ag nanocubes. To find out a perfect range for the simulation is chosen from 400 nm to 900 nm: absorber of visible light, in 2016, Ullah et al. work on plasmonic effect based perfect absorber for solar cell applications relies on a concept that perfect absorber should be free from the reflection as 2.1. Numerical methods well as transmission through the structure [19]. They proposed a fi theoretical polarization independent plasmonic absorber design, A3D nite difference time domain (FDTD) numerical method consist of gold nanorings on the top of the dielectric spacer and a [21] was employed to model the optical effects of metallic nano- fi gold reflector that explored nearly unity absorption in the visible particles suspended on top of the thin lm solar cells. The FDTD fi and near infrared spectrum. More recently, Duan et al. reported the results were used as input to the nite-element time-domain solver light trapping and the light absorption for two different shapes of of the commercially available CST Microwave Studio software. The silver nanoparticles (spheroidal and hemispheroidal) in order to method solves Maxwell's equations over the entire cell. In the FDTD fi improve the light absorption in thin film silicon solar cell. The simulation, the material is de ned in every simulation grid point. fi fi difference of light absorption distribution between the antireflec- All effects related to electromagnetic elds including rear eld, fi fi fi tion coating and the crystalline silicon body was studied [20]. radiating near eld, and scattered eld (or far eld) effects were Though a lot of research works have been done in this area, still taken into account. it is a great challenge to improve the integrated solar cell efficiency Metallic nanoparticles having sizes comparable to the wave- over the whole visible spectrum. In this letter, we propose a plas- length of illuminating light scatter the light preferentially along the monic structure made of silver double nanoparticle system (DNS) incident direction of wave propagation. In this work, we analysed a separated by a small gap suspended onto a silicon substrate. Here, structure consisting of periodic repetition of a system of metallic we varied the size of nanoparticles for optimization and studied double nanoparticle system (DNS), considering the main parame- integrated quantum efficiency by varying the gap between the ters taken as variables for the optimization studies. Fig. 1 represents double nanoparticles, in order to enhance utility of visible spec- a cubical unit cell consisting of two metallic spherical nanoparticles trum. In the first section, we propose our geometry and numerical having an inter-particle separation. This unit cell simulates one simulations to extract the absorption of the structure. In subse- period of a square array of closed packed particles suspended on quent sections, we first discuss the absorption enhancement and top of a silicon solar cell. The FDTD program places the unit cell in a fi resulting integrated absorption enhancement in single and double square box with speci c boundary conditions (BCs) on each face. nano particles system. Then we discuss the power loss in both the On the z-direction boundary conditions are perfectly matched layer ð ; Þ cases and finally we find out an optimized structure for our in- (PML). On the side boundaries x y periodic BCs are used to model fi vestigations in double nano particles system. the in nite periodicity of the structures and the normally incident plane wave source. Here, symmetric and anti-symmetric BCs are used to reduce the required memory size and computation time.