Designing a Multi-Quantum-Dot Array for Efficient Light-Harvesting in Solar Cells

One of the major loss mechanisms leading to low power conversion efficiencies in photovoltaic (PV) devices arises from the limited spectral response of solar cells to the wideband solar spectrum. The capture of photons that otherwise would contribute to thermalization of charge carriers, could be targeted by a luminescent down-shifting (LDS) layer capable to absorb high energy photons and re-emit them at lower energies where the PV material exhibit a significantly better response. In addition, when the LDS layer is placed at the surface, it modifies the reflectance of the solar cell, and consequently, its thickness and refractive index (RI) are key factors in the performance of the resulted PV structure. Thus, for PV applications, the LDS layer must be optimized for the best trade off between the antireflective and LDS capabilities. In this study, we present a new approach to increase the spectral response of a single-junction solar cell by exploiting the size-dependent refractive index and down-shifting capabilities of quantum dots. Compared to a conventional LDS layer, our design allows for thicker films and thus higher optical absorptions, while the reflectance is reduced.