Resumen
The inability of a single-gap solar cell to absorb energies less than the band-gap energy is one of the intrinsic loss mechanisms which limit the conversion efficiency in photovoltaic devices. New approaches to “ultra-high” efficiency solar cells based on artificially engineered materials with designed optoelectronic properties, like semiconductor nanostructures such as multiple quantum wells (MQW) and superlattices (SL) systems in the intrinsic region of a p-i-n cell of wider band-gap energy (barrier or host) semiconductor. These configurations are intended to extend the absorption band beyond the single gap host cell semiconductor. Deviation from bulk behavior needs to be taken into account at the time of describing the device operation mechanisms, a requirement which involves theoretical approaches for the simulation. A theoretical model has been developed to study the performance of the strain-balanced GaAsP/InGaAs/GaAs MQW solar cell, and GaAs/GaInNAs MQW or SL solar cells. These approaches make very attractive for space applications or for triple-junction concentrator photovoltaic cell based on a GaAs/GaInNAs bottom cell that could reach 50% conversion efficiency.
In this talk we also present new types of photovoltaic device where Gaussian superlattice is inserted in the i-region of a GaAs/GaInNAs p-i-n solar cell. A theoretical model is developed to study the performances of these devices. We establish a new criterion to calculate miniband widths in superlattice heterostructures in the presence of electric field. By optimizing miniband width, the spectral response of the cell in the energy region below the absorption edge of host material is significantly enhanced. Our results show that these devices could reach higher conversion efficiencies than the single-gap solar cell.
We are exploring the substitution of superlattices for graphene layers because it has revealed huge promise for future electronics technology besides fundamental physics applications because of its linear energy-momentum dispersion relations that cross at Dirac point. We present a graphene-based multilayer device that greatly magnifies the vertical tunneling transport. The tunnel electrical properties of heterostructures formed between multiple n- and p-doped graphene sheets, with the same rotational alignment, are theoretically investigated. Expressions for the voltage dependence of the tunnel current that flows between the two-dimensional graphene electronic states are derived. At a voltage bias such that the Dirac points of the graphene sheets are aligned, a large resonant current peak is observed.