Carbon nanotubes application as buffer layer in Cu(In,Ga)Se₂ based thin film solar cells

In recent years, numerous alternative materials have been proposed to replace with CdS in chalcopyrite solar cells. In this work, the possible advantages of inserting a carbon nanotube layer as buffer layer in Cu(In,Ga)Se₂ thin film solar cells are investigated. Three mechanisms to improve the open circuit voltage without compromising the short circuit current are discussed: (i) introduction of an energy barrier which is higher for dark current than for light current; (ii) reduction in the density interface states at either sides of this buffer layer compared to the structures without this layer and due to a more favourable position of the Fermi levels at the interface with respect to the band edges (iii) due to the chemical interaction of the materials. The performance parameters turn out to be determined by interface recombination along with the chemical and electrostatic interactions at the interfaces.