Simulation of the functionality of ZnO, TiO₂ and Ta₂O₅, and MoO₂ carrier selective contacts of GaAs_0.99Bi_0.01 nanowire-based solar cells

Abstract The photovoltaic performance of perpendicularly aligned GaAs 0.99 Bi 0.01 /CSC/ITO core–shell nanowire solar cells is thoroughly investigated in this simulation-based theoretical study for both electron-selective contact (ESC) and hole selective contact (HSC) as carrier selective contact (CSC) shell around GaAs 0.99 Bi 0.01 core nanowire. The overall performance is compared with radial p-i-n-doped GaAs 0.99 Bi 0.01 nanowire solar cell (NWSC) to mark the improvement caused by carrier selectivity. ZnO, TiO 2 and Ta 2 O 5 are chosen as ESC material and MoO 2 is chosen as HSC material in order to carry out this comparative study. We have thoroughly performed geometric optimization tests over a wide range of periods in order to select the optimized ITO (indium tin oxide) thickness for obtaining maximum photocurrent generation. A maximum short-circuit photocurrent density ( J sc ) of 38.76 mA cm −2 is obtained with a ZnO coated NWSC for a pitch ( P ) of 400 nm and ITO shell thickness of 90 nm. For this optimized geometry, TiO 2 , Ta 2 O 5 and MoO 2 coated structures offer J sc of 35.82, 35.69 and 35.27 mA cm −2 , respectively, and an uncoated NW exhibits J sc of 31.15 mA cm −2 . The planar structure without coating gives a J sc of 24.86 mA cm −2 , which is significantly lower than the nanostructured solar cells. Finally, a Lumerical 3D charge transport simulator is used to perform electrical stimulation of ZnO-coated structure, which offers maximum ideal J sc . A detailed electrical performance analysis of GaAs 0.99 Bi 0.01 /CSC/ITO unit NW solar cell for ZnO, TiO 2 and Ta 2 O 5 as ESCs and MoO 2 as HSC is also covered in this article. ZnO as an ESC offers the best photo-conversion efficiency (PCE) of ∼25% and open-circuit voltage ( V oc ) of 0.95 V for a very small minority carrier lifetime (Ʈ n ) of 0.1 ns for GaAs 0.99 Bi 0.01 and Ʈ n of 1 ps for ZnO, with high surface recombination velocity of 10 5 cm s −1 at the interfaces.