Experimental Evidence of Complex Energy-Level Structuring in Quantum Dot Intermediate Band Solar Cells

III-V quantum dot systems are widely studied to implement the promising intermediate band solar cell concept. However, current performances are quite lower than theoretical expectations, and several loss mechanisms were proposed to explain the experimental findings. Here we show that quantum dot solar cells are far from a simple intermediate band system because of complex energy structuring. Thanks to the combination of high-quality heterostructures and high-resolution modulation spectroscopy, we experimentally unveil specific resonances, hidden upon continuous wave spectroscopy inspection because of ensemble effects and thermal broadening. These resonances are associated with strain-induced localized states and to crossed transitions and arise from the coexistence of materials with different dimensionalities (i.e., nanostructures, wetting layers, and continuum). The study clearly shows that accurate energy structuring modeling is required for these systems to be effectively considered as intermediate band solar cell solutions.