Ultra-Thin Plasmonic Optoelectronic Devices

Abstract

AbstractAn important challenge for lowering the cost of “solar energy” is minimising the required usage of the “active solar absorber material.” Development of ultra-thin solar cells is of paramount importance in ultimate cost reduction of solar cells—without compromising if not increasing, the efficiency of solar cells. Research in ultra-thin solar cells is fast-gaining ground. It was pointed out that basing on Thomas–Reiche–Kuhn sum rule, the amount of material required to achieve maximum optical absorption due to incident light (in the spectral region of interest for solar cells) may well be around 10 nm thick. However, it is important to devise appropriate light manipulation mechanism in conjunction with the semiconductor absorber layer of the solar cells. Plasmonics—the science and technology of confining the electric field energy in low-dimensional systems—is an important route to successfully achieve the “ultra-thin solar cells”. Plasmonics offer two routes for light manipulation—near field and far field. These mechanisms in turn enable more secondary mechanisms such as hot-carrier generation, photon up-conversion, nonlinear effects, etc. When employed optimally, these mechanisms will aid one another producing the amplifying effect on the optical absorption in the active semiconductor absorptive layer of solar cell and consequently on the efficiency of the cell. Availability of methodology and techniques for easily and cost-effectively incorporating plasmonic structure in the immediate vicinity of the semiconductor absorber of the solar cell is one of the limiting factors in achieving the ultra-thin solar cells. Plasmonic metasurfaces—2D analog of plasmonic metamaterials—are found to possess broadband optical properties required for solar cells. There is a growing body of research to implement plasmonic light trapping effects on various inorganic and organic ultra-thin solar cells. We will discuss various plasmonic light trapping mechanisms with respect to solar cells and possible directions to successful implementation in various types of industrially important solar cells.In this chapter, we will describe the following aspects: (1) concept behind plasmonic photon management, innovative plasmonic structures to confine, scatter light and modify electric field; 2D multilayers, core–shell structures, custom-designed textures and topography; (2) characterisation methods to probe the plasmonic effects, diagnosis tools employing plasmonic effects; (3) solar cell structures, adapting fabrication process of the first-generation and second-generation solar cells in the market, to make effective use of plasmonic light trapping through both far field and near effects, absorber material consideration, assessment of optical gain compared to plasmonic loss and evolution of electronic/structural defects and shunt paths; (4) challenge of upscaling and industrial plasmonic PV fabrication tool; (5) other practical/potential applications: LED, water splitting, third- and future generation solar cells, special emphasis on up-conversion; and (6) industrial viability of the plasmonic-based devices, compared to existing scenario.This chapter will explain how dimension on optoelectronic devices can be substantially thinned down by increasing light trapping efficiency through plasmonic effects.