The Role of Defects on the Performance of Quantum Dot Intermediate Band Solar Cells

Electrically active defects present in three InAs/GaAs quantum dots (QDs) intermediate band solar cells grown by metalorganic vapor phase epitaxy have been investigated. The devices' structures are almost identical, differing only in the growth temperature and thickness of the GaAs layers that cover each InAs QD layer. These differences induce significant changes in the solar energy conversion efficiency of the photovoltaic cells, as previously reported. In this work, a systematic investigation was carried out using deep level transient spectroscopy (DLTS) and Laplace DLTS measurements on control samples and solar cell devices, which have clearly shown that electrically active traps play an important role in the device figures of merit, such as open circuit voltage, short circuit current, and shunt resistance. In particular, it was found that the well-known EL2 defect negatively affects both the open circuit voltage and shunt resistance, more in structures containing QDs, as a consequence of the temperature cycle required to deposit them. Other unidentified defects, that are absent in samples in which the QDs were annealed at 700 degrees C, contribute to a reduction of the short circuit current, as they increase the Shockley-Read-Hall recombination. Photoluminescence results further support the DLTS-based assignments.

Automated summary

Investigation on electrically active defects in three InAs/GaAs quantum dots intermediate band solar cells grown by metalorganic vapor phase epitaxy reveals the significant impact of electrically active traps on device performance, particularly the negative effects of the well-known EL2 defect on open circuit voltage and shunt resistance. Other unidentified defects were found to reduce short circuit current, contributing to increased Shockley-Read-Hall recombination. Photoluminescence results support the DLTS-based assignments.