5.9. Metallic nanoparticles (plasmonic effect)
Nanotechnology plays an important role in enhancing the efficiency of solar cell. Si is poor in absorbing infrared light and thus most of solar light is wasted and thus increased thickness of the material is required. To reduce this problem or to decrease the thickness of thin film solar cell, metallic nanoparticles are used on the top of active layer which have the strong ability to scatter the incident light. This is also called plasmonic effect. Mainly Ag nanoparticles are used in enhancing the efficiency of TFSC. The nanoparticles behave like small mirror; concentrate light more strongly than normal mirrors. This effect is based on surface plasmon, the collective motion of electrons [36], [75], [76] and [77]. Nanoparticles have a particular frequency called resonant frequency at which incident light will strongly excite the collective oscillation of electrons [78] and [79]. This causes strong absorption or strong scattering of light. When light falls on the surface of solar cell it is scattered in different directions. These nanoparticles preferentially scatter light into high index material leading to enhance coupling with underlying semiconductor and thus reduces reflectance over a broad spectral range. In nanoparticles, scattering is stronger. Fig. 11 describe the scattering from metal nano-particles at the surface of solar cell [54] and [57].