Design of wide bandgap (1.7 eV-1.9 eV) III-V dilute nitride quantum-engineered solar cells for tandem application with silicon

Abstract

Here we study photovoltaic properties of GaInPNAs based quantum well and superlattice solar cells, that are either strainbalanced or lattice matched to silicon and evaluate their potential towards the development of high-efficiency tandem operating in conjunction with a silicon bottom cell. Quaternary dilute nitride compound semiconductors like GaAs y P 1-x-y N x and Ga 1-z In z P 1-x N x are lattice matched with silicon at y=4.7*x-0.1, z=2.2*x-0.044 and have direct bandgap (with N<0.6%); thus, allowing monolithic integration of III-V optoelectronics with silicon technology and IIIV/Si tandem solar cells. Applying eight band k.p strained Hamiltonian, for both tensile and compressive strain, and Band Anti-crossing (BAC) model to the conduction band, in order to account for small amounts of nitrogen impurities, the electronic band structure and dispersion relation of these alloys can be determined. With small amount of nitrogen (<5%), bandgaps of these alloys lattice matching with silicon fulfil the optimum bandgap (1.7-1.9) eV requirement for III-V/Si tandem solar cell. Confinement energies in quantum structures can be computed using the transfer matrix approach. Optical absorption is evaluated by taking into account the inter-band transitions in the quantum well and barrier region, including excitonic transitions, using the fermi golden rule for both TE and TM polarization of incident light. Using these properties, we can determine whether the possible integration of p-i-n MQWs (or SL) solar cell on silicon is favorable by evaluating the predicted quantum efficiency and photo-current. The designs for a tandem III-V-N/Si represent an opportunity for achieving practical efficiencies of more than 30% under AM 1.5G spectrum.