Question

Explain why several semiconductor materials might be put together to obtain more efficient solar cells.

Answer 1

The Solar cells is an electronic device based which works by the photovoltaic effect..The light from the sun falls on the semiconductor junction, the n-type semiconductor material has high concentration of electrons and the p-type semiconductor has low concentration of electrons. When light falls on n-type semiconductor electrons from n side flows to p side resulting in current flow.

Solar cells can be divided into two types
1. Single junction
2. Multi Junction

The light from the sun has several wavelengths but a single junction solar cell can only receive one type of wavelength and the efficiency is limited. The maximum efficiency a single junction solar cell can be achieved is 34%. Comparitively a Multi junction solar cell can harvest multiple wavelengths of solar radiation and generate current. Within limited space a multi junction solar cell contains several p-n junctions containing several materials like  gallium indium phosphide (GaInP), indium gallium arsenide (InGaAs), germanium (Ge) and not silicon which is primarily used in Single junction solar cells.

At present a three junction Solar cell achieved 45% efficiency but with more junctions the efficiency can be achieved upto 70%.