Multi-junction solar cell with Dilute Nitride cascaded quantum wells design

Abstract

Previously, and under the assumption of complete carrier collection from wells, we have shown that III–V Dilute Nitride GaAsN multi-quantum well (MQW) structures included in the i-region of the third cell in a 4 junction configuration (InGaP/GaAs/ (MQW)/ Ge) could yield 1 sun efficiencies greater than 40%. However for a conventional deep well design the characteristic carrier escape times could exceed that of radiative recombination hence possibly limiting the operation of the proposed device. In order to overcome this limitation here we evaluate a new cascaded quantum well design whereby a thermally assisted resonant tunneling process is used to accelerate the carrier escape process (<30ps) and hence improve the photo generated carrier collection efficiency. The quantum efficiency of a p-i-n subcell where a periodic sequence of quantum wells with well and barrier thicknesses adjusted for the cascaded operation is extracted using a 2D drift diffusion model and taking into account absorption properties of resulting MQWs. The calculation also accounts for the E-field induced modifications of absorption properties and quantization in quantum wells. The results are then accounted for to calculated efficiencies for the proposed 4 junction design, and indicate potential for reaching efficiencies in excess of this structure is above 42% (1 sun) and above 50% (500 sun) AM1.5.