Numerical modeling of axial junction compositionally graded InxGa1−xN nanorod solar cells

In this work, the performance of compositionally graded axial junction In_xGa_1-xN nanorod solar cells with an absorber region of In_0.45Ga_0.55N (Eg~1.8eV) is examined using the finite element semiconductor device simulation software Taurus Medici from Synopsys^®. While nanorod structures can provide significant strain relief resulting in excellent crystalline quality of the typically defect-ridden full-spectrum InGaN ternary semiconductor alloy, we show that other considerations must be taken into account to justify the use of InGaN axial junction nanorods for photovoltaic applications. Without considering light trapping effects, the reduction in junction area can significantly limit the collection efficiency of the nanorods. Further, the greater periphery surface area of the nanorods can lead to substantial increase in surface recombination with significant decline in the short-circuit current density J_sc and the open-circuit voltage V_oc for the simulated device structure. Even with a predefined zero surface recombination velocity, the proximity of the nanorod circumferential surface to the axial junction can lead to electric field fringing effects that degrade the V_oc. In all, surface recombination is found to be the major factor limiting the performance of the In_xGa_1-xN axial junction nanorod solar cells examined.