Defects present in structures of intermediate band (IB) solar cells of GaAs with InAs quantum dots (QDs) grown by MOVPE have been investigated. The three studied IB solar cells differ in the growth temperature of the spacer layers that separate the InAs QD layers in the active region and the thickness of the thin layer that capping each QD layer. Previously, the energy conversion efficiencies of these cells were measured and the cell with the highest spacer layer-growth temperature (700 C degrees) and thinner capping layer (3 nm) showed the highest efficiency, about 6.9 percent. The cells with thicker capping layers (6 nm) showed lower efficiencies, one of them, with spacer layers grown at 700 C degrees, reaching 5.1 percent, and the other one, with spacer layers grown at 600 C degrees, reaching only 2.8 percent. In this work, DLTS and Laplace DLTS studies show that the cell with the lowest efficiency has the largest number and highest concentrations of defects, unlike the other two cells, which have only one trap, EL2, in lower concentrations. These results demonstrate that the different growth conditions are determinant for the formation of defects and that the defect reduction leads to the increase of the IB solar cell efficiencies. Other samples were also grown and studied by the same techniques: three solar cells with identical structure as the IB solar cells, but without QDs, and individually doped GaAs samples that represent the p and n contact sides of the IB solar cells. From the study of the cells without QDs, the origin of some defects in the IB solar cells was found to be related to the QD growth conditions or related to the spacer layer-growth temperature. The study of the GaAs samples indicated the presence of defects in the p and n sides that could trap photo-excited carriers collected through these contacts during cell operation and thus reduce the efficiency. The results of this work allow developing new strategies to improve the epitaxial growth quality of IB solar cells in the laboratory of semiconductors LabSem of PUC-Rio where the studied samples were grown.