We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to $\sim 6000\mathrm{nm}$. To our knowledge, this is the broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidence indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable.

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude.In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance.The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells.

Current prototypes of quantum-dot intermediate band solar cells suffer from voltage reduction due to the existence of thermal carrier escape. An enlarged subbandgap E _L would not only minimize this problem but would lead to a bandgap distribution that exploits more efficiently the solar spectrum. In this study, we demonstrate InAs/InGaP QD-IBSC prototypes with the following bandgap distribution: E _G = 1.88 eV, E _H = 1.26 eV, and E _L > 0.4 eV. We have measured, for the first time in this material, both the interband and intraband transitions by means of photocurrent experiments. The activation energy of the carrier thermal escape in our devices has also been measured. It is found that its value, compared with InAs/GaAs-based prototypes, does not follow the increase in E _L . The benefits of using thin-AlGaAs barriers before and after the quantum-dot layers are analyzed.

Current matching is crucial to maximize the efficiency of two‐terminal multi‐junction photovoltaic devices. However, even in perfectly designed devices, deviation from the target operating temperature and consequent changes in the subcell absorptances causes current mismatch between the subcell currents even at constant spectral conditions. Fortunately, luminescence coupling from current‐overproducing subcells to current limiting subcells mitigates this effect. In this work, the coupling process efficiency in three‐junction photonic power converters based on GaAs/AlGaAs rear hetero‐junction subcells is experimentally quantified. A coupling process efficiency of 32% ± 9% from top and middle subcells to the limiting bottom subcell is found. Under constant monochromatic illumination, the observed coupling reduces the current mismatch, induced by raising the temperature from current matched conditions at 25°C to 70°C, from 4.4% to 1.6%. Furthermore, in this work, three‐junction photonic power converters with back surface reflectors are implemented. Those reflectors improve the device response at elevated temperatures by increasing the optical path length in the limiting subcell. It is shown experimentally how a back reflector effectively redirects photons that are emitted by the bottom subcell towards the upper subcells to reinforce luminescence coupling.