Nondestructive characterization of threading dislocations in graded buffer layers of inverted metamorphic solar cells by two-photon excitation spectroscopy

In order to realize lattice-mismatched solar cells with high conversion efficiencies, it is necessary to characterize the threading dislocations generated at the interfaces between materials with different lattice constants. We report on the characterization of threading dislocations in the step-graded buffers of lattice-mismatched solar cells by two-photon excitation photoluminescence imaging. The threading dislocation density in the buffer layer nearest to the active layer of our single-junction solar cell with an open-circuit voltage of Voc = 0.562 V was 3.3 × 106 cm−2 and that for the device with Voc = 0.415 V was 7.0 × 106 cm−2.