Light Trapping Design in Silicon-Based Solar Cells

When the sunlight illuminates the front surface of solar cell, part of the incident energy reflects from the surface, and part of incident energy transmits to the inside of solar cell and converts into electrical energy. Typically, the reflectivity of bare silicon surface is quite higher; more than 30% of incident sunlight can be reflected. In order to reduce the reflection loss on the surface of solar cell, usually the following methods were adopted. One is to corrode and texture the front surface [Gangopadhyay et al., 2007; Ju et al., 2008; Basu et al., 2010; Li et al., 2011], so that incident light can reflect back and forth between the inclined surfaces, which will increase the interaction between incident light and semiconductor surface. The second is coated with a single-layer or multi-layer antireflection film coating [Chao et al., 2010]. Generally, these coatings are very thin, the optical thickness is nearly quarter or half of incident wavelength. Single-layer antireflection coating only has good anti-reflection effect for a single wavelength, so multi-layer antireflection coating is commonly used in high efficiency solar cells, for it has good anti-reflection effect within the wide spectrum of solar radiation. Third, surface plasmons offer a novel way of light trapping by using metal nanoparticles to enhance absorption or light extraction in thin film solar cell structures [Derkacs et al., 2006; Catchpole et al., 2008; Moulin et al.,2008; Nkayama et al.,2008; Losurdo et al.,2009;]. By manipulating their size, the particles can be used as an efficient scattering layer. One of the benefits of this light trapping approach is that the surface area of silicon and surface passivation layer remain the same for a planar cell, so surface recombination losses are not expect to increase. The above light tapping methods can be used individually or in combination. In the following section we will introduce them in detail.