Interface State Density
Interface recombination at a heterojunction interface is frequently the main loss mechanism in heterojunction solar cells. If the number of defect states at the heterojunction interface can be reduced, the solar cell efficiency increases significantly.
If one is able to shift the Fermi energy position at the interface as a function of an externally applied voltage, one can measure the corresponding interface state density via voltage dependent surface photovoltage, VD-SPV.
Fig.1 shows typical interface state density distributions of SiO2/c-Si and a-Si:H/c-Si heterostructures.