Design and Non‐Lithographic Fabrication of Light Trapping Structures for Thin Film Silicon Solar Cells

Abstract

Along with increasing fossil-fuel consumption and greenhouse gas emissions, sustainable energy research has been a global topic for many years. Among all the renewable energy sources, solar energy has been attracting widespread attention because of its abundance, stability and environmental friendliness. Nowadays, more than 90% of the photovoltaic market is dominated by wafer-based silicon solar cells. The cost of this technique, which is dominated by the starting material, is diffi cult to reduce. [ 1 ] Thin fi lm silicon solar cells have an active layer of only several micrometers thick and are believed to be a promising candidate for further cost reduction while maintaining the advantages of bulk silicon. [ 2 ] However, the effi ciency of thin fi lm silicon solar cells critically depends on optical absorption in the silicon layer since silicon has low absorption coeffi cient in the red and near-infrared (IR) wavelength ranges due to its indirect bandgap nature. Therefore, an effective light trapping design is indispensable to achieve high effi ciency modules. To address this problem, several methods are used in current technology, for example, traditional schemes such as textured transparent conductive oxide (TCO) and metal refl ector. [ 3 ] These methods are diffi cult to precisely control and optimize the textured surface. In addition, some other issues should be considered such as enhanced surface recombination due to the roughness of silicon layer [ 4 ] and parasitic loss at the TCO/metal interface. [ 5 ] One, two and three dimensional photonic crystals have also been proposed to enhance the light trapping, [ 6 ] but this design is very diffi cult to be implemented experimentally. A practical approach for light trapping has been demonstrated using diffractive grating structures on the backside of a silicon cell. [ 7 ] However, interference lithography and high temperature processing were usually employed in fabricating this structure, limiting its scalability to large area applications. Previously, we reported fabrication of gratings using self-assembled porous alumina for light trapping in silicon solar cells. [ 8 ] However, the low refractive index of alumina ( n ∼ 1.7) has limited the diffraction effect. Furthermore, in production solar cells the electrolyte used in the anodization process reacts with the TCO resulting in device degradation. To achieve a stronger light trapping effect in production Si thin fi lm solar cell structures while exploiting a more controllable and reliable method for fabrication, here we design a backside photonic structure consisting of a high-index-contrast diffraction grating and a distributed Bragg Refl ector (DBR). We optimize the structure in a thin fi lm microcrystalline silicon ( μ c-Si) solar cell, and implement the design experimentally using a self-assembled mask to demonstrate signifi cantly enhanced cell effi ciency due to increased optical path length. The light trapping structures lead to a signifi cant increase of photon absorption in the red and near-infrared ...

Tunable photovoltaic effect and solar cell performance of self-doped perovskite SrTiO3

“…These values are much higher than those obtained so far in junctions based on similar perovskite oxides, such as BFO. [10][11][12] Further improvement of the power conversion efficiency could be achieved by increasing the optical absorption in the visible range, for instance by making use nanoscale surface engineering for light trapping [40][41][42] or other strategies like plasmonics enhancement. 43 In summary, the PV performance of Schottky heterojunctions based on self-doped STO single crystals was systematically investigated.…”

Extraordinary Light-Trapping Enhancement in Silicon Solar Cell Patterned with Graded Photonic Super-Crystals

“…For photovoltaic devices, nanostructuring the active layers has generated high local density of optical states in the absorber layer, allowing for more energy to be coupled into the solar cell and absorbed [10][11][12][13][14]. The appearance of many photonic bands, up to 144, below the photonic band gap or cavity mode [25] indicates a large density of optical states in the GPSC.…”

“…Nanostructures have been used to improve light coupling from free space to silicon-based photovoltaic solar cell devices and incorporate light-trapping functionality in the solar cell so that the light absorption of the device will increase. Various nanostructures have been proposed and their mechanisms for light absorption enhancement have been investigated, which include surface plasmon induced enhancement [1], nanowire-based light trapping [2][3][4], back-reflector-based multiple pass absorption [5][6][7][8][9], and one-dimension and two-dimension photonic crystal-based structural resonances [10][11][12][13][14]. Photonic crystals are periodic structures that offer powerful photon control and manipulation capability [10,11].…”

“…Photonic crystals are periodic structures that offer powerful photon control and manipulation capability [10,11]. The structural resonances in simple photonic crystals offer a series of sharp resonances at a specific wavelengths and angles [10][11][12][13][14]. By incorporating dual lattice or so-called superlattice structures into photonic crystals, the spectral response of the photon-lattice interactions can be broadened [15][16][17][18].…”

Research Background and Motivation

“…Based on this property, manipulation of the light transmission in a designed route within a target frequency light range becomes possible, and examples include photonic crystal wave guides and photonic crystal fibers [107]. Recently, photonic crystals, which was fabricated using anodic porous alumina as a template, has been used in enhanced light trapping in thin film solar cells [108]. Stronger light absorption in the red and near-IR spectral ranges was detected with a 21 % increase in the energy conversion efficiency [108].…”