Optimized band gap for solar cells is close to 1.5 eV. Some of the common materials for solar cells are

1. silicon (Si), E_G = 1.12 eV – currently the most popular material but has low absorption coefficient and high temperature dependence,

2. gallium arsenide (GaAs), E_G = 1.42 eV - by far the most widely used, especially for high end applications like satellites. Its absorption coefficient is about ten times better than silicon and doesn’t have the same temperature dependence.

3. copper-indium diselenide (CIS), E_G = 1.01 eV – has the highest optical absorption, but gallium is introduced in the lattice to raise the band gap energy closer to the solar ideal. This resulted in the popular copper-indium-gallium diselenide (Culn- GaSe₂ or CIGS) material for photovoltaic cell. By variation of Ga fraction, a band gap of around 1.48 eV has been achieved.

4. cadmium telluride (CdTe), E_G = 1.44 eVmade from the II-VI group elements.

[Notes : (1) By far the most widely used III-V solar cell is gallium arsenide (GaAs). Other IIIV semiconductors-indium phosphide (InP), gallium antimonide (GaSb), aluminium gallium arsenide (AlGaAs), indium gallium phosphide (InGaP), and indium gallium arsenide (InGaAs)-exchange group III elements to make different band gap energies. III-V semiconductors offer a great host of advantages over silicon as a material for photovoltaics. However, the biggest drawback is cost. (2) The theoretical limit on the thermodynamic efficiency of single-junction solar cells is ~ 30%. Hence, today’s most efficient technology for the generation of electricity from solar radiation is the use of multi-junction solar cells made of III-V compound semiconductors. Efficiencies up to 39% have al-ready been reported under concentrated sunlight. These solar cells have initially been developed for powering satellites in space and are now starting to explore the terrestrial energy market through the use of photovoltaic concentrator systems. A triple-junction solar cell,

Ga_0.35 In_0.65 P/Ga_0.83 In_0.17 As/Ge, has been demonstrated by a conversion efficiency of 41.1% at 454 kW/m²]