chapter  6
8 Pages

Attempts to Build Light Energy Conversion Devices

WithSomnath Paul, Chirantan Samajdar, Tapan Ganguly

Photonics plays a significant role in energy conversion process. The enormous energy of the sun can be utilized in the three main ways. They are (1) conversion of sunlight to electrical power, (2) conversion of sunlight to thermal power and (3) conversion of sunlight directly to fuels. Most solar cells work on the basis of conversion of sunlight into electricity using the PV effect. The most important commercially available PV materials systems today are based on inorganic semiconductors. The majority of solar modules are based on silicon, which is the second most abundant material in the earth, and the efficiency of silicon solar cell is nearly 25.6%. Photonics plays an important role in Si-based solar cells and modules since it is an indirect band gap semiconductor and hence has a relatively long absorption depth across the solar spectrum. Most importantly, light-trapping structures must be fashioned on the front surface of the wafers to ensure that long wavelength light is adequately trapped within the solar cell and is not lost from reflection at the back contact. Lately low-cost dye-sensitized solar cells (DSSCs) have attracted much attention with their relatively high energy conversion efficiencies. One of the major advantages of DSSC is that by varying the combinations of the dyes and semiconductor materials, the cell performance can be improved. Many attempts have been made to synthesize alternative molecular dyes to extend the spectral response, but the low absorption cross section and instability under strong illumination inhibited significant efficiency increase.